The Periodic Table : 10,001 questions

Noble Gases: Characterisitcs and Properties

2017-09-22T02:14:00.001-07:00

Introduction

* What are noble gases?

* Why are they called "inert" gases?

* Who discovered them?

* Who named them?

Body

Noble gases are highly nonreactive gases as the shells of these noble elements dont have any place for any other electron. that means that their last shell is completely filled with the number of electron required in the last shell. they are also called inert gases due to its highly nonreactive property. They all exist in gases form. They were discovered after long time due to their nonreactive property.

Position of Noble Gases in Periodic Table

Characteristics and Properties of Noble Gases

Conclusion

List of representative elements in the Periodic Table?

2014-05-16T02:46:00.004-07:00

The following is a list of all elements in the periodic table that are representative elements.

Hydrogen, Helium, Lithium, Berillium, Boron, Carbon, Nitrogen, Oxygen, Florine, Neon, Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulfur, Chlorine, Argon, Potassium, Calcium, Gallium, Germanium, Arsenic, Selenium, Bromine, Krypton, Rubidium, Strontium, Indium, Tin, Antimony, Tellurium, Iodine, Xenon, Cesium, Barium, Thallium, Lead, Bismuth, Polonuim, Astatine, Radon, Francium and Radon.

According to groups these are:

In group 1 (alkali metals): Hydrogen, Lithium, Sodium, Potassium, Rubidium, Cesium, Francium
In group 2 (alkaline earth metals): Berillium, Magnesium, Calcium, Strontium, Barium, Radium,
In group 13 (boron family): Boron, Aluminum, Gallium, Indium, Thallium
In group 14 (carbon family): Carbon, Silicon, Germanium, Tin, Lead
In group 15 (nitrogen family): Nitrogen, Phosphorous, Arsenic, Antimony, Bismuth
In group 16 (oxygen family): Oxygen, Sulfur, Selenium, Tellurium, Polonium
In group 17 (halogens): Fluorine, Chlorine, Bromine, Iodine, Astatine
In group 18 (noble gases): Helium, Neon, Argon, Krypton, Xenon, Radon

According to rows these are:

Period 1: Hydrogen, Helium
Period 2: Lithium, Berillium, Boron, Carbon, Nitrogen, Oxygen, Florine, Neon
Period 3: Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulfur, Chlorine, Argon
Period 4: Potassium, Calcium, Gallium, Germanium, Arsenic, Selenium, Bromine, Krypton
Period 5: Rubidium, Strontium, Indium, Tin, Antimony, Tellurium, Iodine, Xenon
Period 6: Cesium, Barium, Thallium, Lead, Bismuth, Polonuim, Astatine, Radon, Francium and Radon

What is the reason that atomic size varies among the elements of the periodic table?

2014-05-16T02:37:00.002-07:00

The atomic size of an element depends two things:

Number of electron orbits around the nucleus
Nuclear charge

Each of these reasons are explained below.

Number of electron orbits around the nucleus

The electrons in an atom are arranged around the nucleus in different levels called shells or orbits. For example, in a sodium (Na - 11) atom, there are a total of 11 electrons that are arranged in three successive orbits around the nucleus shown by the following diagram:

Sodium atom with three orbits

The more the number of orbits, the lager is the atomic size. For example, potassium, which has four electron orbits, one more than sodium, has a larger atomic size than sodium:

Potassium atom with four orbits

Thus we can conclude that the atomic size varies in the periodic table with the number of electron orbits. In the periodic table, the row number of an element is equal to the number of electron orbits present in its atom. Thus, as mentioned above, sodium, being in the third period, has three orbits while potassium, being in the fourth row, has four orbits.

Thus the atomic size of elements of elements increases as you move down in the groups (columns) of the periodic table.

Nuclear Charge

The atomic size of an element depends on the nuclear charge. Nuclear charge is the number of protons int the nucleus. The more the number of protons in the nucleus, more is the attractive pull on electrons around it. So out of two elements having the same number of electron orbits, the one with the greater nuclear charge has the lesser atomic size.

For example, magnesium (Mg - 12) and alumnium (Al - 13) both have the same number of orbits (since both are in the third row of the periodic table and hence both have three orbits in their atoms). But aluminium has greater atomic number (13) than magnesium (12) which means that there are more number of protons in an aluminum nucleus than in a magnesium nucleus. Thus the attractive pull between the nucleus and outer electrons in aluminum atoms is greater than in magnesium. As a result, the electron orbits in aluminum atoms move closer to the nucleus than in magnesium.

Thus two elements having the same number of orbits have different atomic sizes based on their respective nuclear charges; The one with greater nuclear charge has smaller atomic size than the one with lesser nuclear charge.

What are alkali metals on the periodic table?

2012-11-11T02:39:00.002-08:00

Alkali metals are all the elements present in the first group of the periodic table.
Alkali metals in order from top to bottom are Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr).

Chemical properties of alkali metals:

Alkali metals are electropositive in nature. This means that the atoms of these elements tend to lose their valence electrons and form positively charged ions.
Alkali metals donate one electron to form positive ions during chemical reactions or in their solutions

Alkali metals form ionic compounds with non metals
Alkali metals combine with halogens or group 7 non metals to form strong ionic salts. For example Lithium Fluoride (LiF), Sodium Chlordine (NaCl), Potassium Chloride(KCl), potassium iodide (KI), etc.
Alkali metals when dissolved in water react to form their respective metal alkalis and liberate hydrogen. For example when sodium metal is dissolved in water it forms sodium hydroxide, a powerful alkali: 2Na + 2H2O -> 2NaOH + H2

Physical properties of alkali metals:

Alkali metals have low melting and boiling points
Alkali metals are malleable, ductile and can be cut with the help of a knife
Alkali metals are lustrous, but their lustrous surface gets oxidized quickly on exposure to the atmosphere and so they appear as dull, white colored metals after a few seconds of cutting them.

Why do alkali metals include hydrogen, even though hydrogen is a nonmetal?

The elements are arranged in the periodic table in increasing order of their atomic numbers, and so atomic number forms the basis of arrangement of elements in the periodic table. Since atomic number of an element relates closely to its valency, electronegativity and chemical properties, the arrangement of elements in the periodic table is affected by their valency, elect negativity and chemical properties as well, although not based on it. Hydrogen although being a non metallic gas by physical nature, has a valency of +1, that is, it’s atoms have only one electron in their outermost shells, which it loses during chemical reactions to form positively charged ions. This is the case with all the alkali metals in the periodic table and no other element except the alkali metals including hydrogen show this characteristic in the periodic table. Due to this property hydrogen atoms behave like metal atoms in chemical reactions with other non metals, similar to the nature of alkali metals. Thus it is appropriate to place hydrogen in the alkali metals of the periodic table.

Placing hydrogen with helium would break the rule of having elements of similar chemical properties and valencies in one group of the periodic table.

Which similar properties do alkali metals exhibit?

2012-10-05T03:42:00.001-07:00

Alkali metals exhibit a number of similar physical and chemical properties:

Electronic configuration

Each alkali metal has a single valence electron. The inner shells of their atoms are filled with electrons to their capacity (octet/duplet). Thus during chemical reactions the alkali metals tend to lose their outermost electron to get a balanced electronic configuration. In doing so, they form positively charged ions.

The general electronic configuration of alkali metals can be written as [Noble gas] ns¹, since the outermost electron in each alkali metal atom goes to the ns-orbital.

Atomic properties

Atomic properties of alkali metals exhibit a gradual gradation from top to bottom. The atomic radius increases gradually from 152 pm for Lithium to 265 pm for Cesium. Similarly the ionic radius also increases from top to bottom, starting from 76 pm for Lithium to 167 pm for Cesium.

Alkali metals have the greatest atomic as well as ionic radii in their respective rows because the nuclear charge (pull) on the valence shell increases on moving from left to right in a row due to increase in the atomic number, whereas the number of shells in each atom remains the same throughout the row. Thus, on moving from left to right, the increasing nuclear charge in each element's atoms pulls the electron shells closer to itself, thereby decreasing the atomic/ionic radii.

Alkali metals have atomic radius greater than ionic radius for each atom, because they form ions by loosing their single valence electron, which reduces the number of electron shells and increases the amount of positive charge in the nucleus attracting the electron shells closer to it.

Physical properties

Alkali metals have low melting and boiling points and densities. This is due to the fact that inter-atomic forces between atoms are weak owing to the presence of a single valence electron in all atoms, which weakens the formation of metallic bonds (same atom bonds) within the same atoms.

With respect to variation, melting and boiling points decrease down the group and density increases down the group.

All alkali metals are lustrous: they are silvery white metals which when freshly cut show a lustrous surface, as on exposure to air they get oxidized quickly and thus loose their luster. They are malleable and ductile and can be cut with a knife.

Electronegativity

Alkali metals have low electronegativities because their atomic sizes are large and they have only one valence electron, so the nuclear pull on the valence electron is less and it tends to get donated to other electronegative atoms during chemical reactions.

What are alkali metals?

2012-10-05T02:49:00.000-07:00

All the elements present in the first group of the periodic table are called alkali metals.

The alkali metals from top to bottom are:

Hydrogen (H)
Lithium (Li)
Sodium (Na)
Potassium (K)
Rubidium (Rb)
Cesium (Cs)
Francium (Fr)

Since alkali metals are present in the first group, they have the same number of valence electrons in their atoms. For the same reason alkali metals show similarity in physical and chemical properties. For example, alkali metals all have a valency of +1, alkali metals are all transparent white lustrous metals, alkali metals are highly chemically reactive; They react with oxygen as soon as they are exposed to air, react with water to form their respective hydroxides; Their hydroxides are all strong alkali's.

What are halogens?

2012-10-05T01:44:00.000-07:00

Halogens are a group of elements present in the seventeenth column of the periodic table. These elements are known as halogens because on reacting with alkali metals, they product different metal salts: The term 'halo' implies 'salt' and 'gens' implies 'producers'. Thus, halogens means salt producers. For example, chlorine (Cl), the first halogen, reacts with sodium to product the salt sodium chloride:

Na + Cl -> NaCl

The list of halogens from top to bottom in the periodic table is as follows:

Fluorine (F)
Chlorine (Cl)
Bromine (Br)
Iodine (I)
Astatine (At)

Halogens are pure nonmetals. These are electronegative elements. In chemical reactions they tend to gain electrons in the outermost shell of their atoms to produce negatively charged ions. Since these elements form negatively charged ions easily, they form many ionic compounds.

What are moles in chemistry?

2011-02-12T22:36:00.000-08:00

A mole is a unit of the quantity of matter. It is a unit that expresses the amount of matter. One mole of a substance is equal to the amount of that substance that has 6.022e23 entities in it. By entities we mean the basic particles of a substance; elements have atoms and compounds have molecules. Therefore one mole of an element is 6.022e23 atoms of that element and one mole of a compound is 6.022e23 molecules of that compound. 6.022e23 is Avogadro's number.

The mole concept in chemistry states that the amount of a substance equal to one mole of it will have a mass equal to its relative molecular or atomic mass (according to whether it is an element or a compound) expressed in grams instead of Atomic Mass Units. Therefore one mole of Hydrogen atoms (H) will have a mass of 1 grams and 1 mole of Oxygen molecules (O2) will have a mass of 16 grams approximately.

Example of a question relating to mole concept in chemistry:

Find the mass of water that will form from 3 moles of Hydrogen reacting with sufficient Oxygen according to the chemical equation:

H2 + O2 -> H2O

Solution:

First balancing the chemical equation, we get:

2H2 + O2 -> 2H2O

Now since 2 molecules of Hydrogen (H2) form 2 molecules of water (H2O) therefore 3 moles of Hydrogen forms 3 moles of water. Mass of 3 moles of water is:
Molecular mass of water is: 2(1) + 16 = 18
Therefore 1 mole of water molecules has a mass of 18 grams.
Therefore 3 moles of water molecules have a mass of 3 * 18 = 54 grams.

Therefore 3 moles of hydrogen molecules on reaction with oxygen form 54 grams of water molecules.

What is the list of all elements in the periodic table?

2010-12-28T07:37:00.000-08:00

The complete list of all elements in the periodic table is given below. Many more useful lists of elements are also given:

All of the following list of elements are arranged in increasing order of their atomic numbers, as in the periodic table.

List of all elements:

Hydrogen, Helium, Lithium, Berlillium, Boron, Carbon, Nitrogen, Oxygen, Flourine, Neon, Sodium, Magnesium, Aluminum, Silicon, Phosphorus, Sulfur, Chlorine, Argon, Potassium, Calcium, Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper, Zinc, Gallium, Germanium, Arsenic, Selenium, Bromium, Krypton, Rubidium, Strontium, Yttrium, Zirconium, Niobium, Mollybdenum, Telerium, Rutherfordium, Rhodium, Palladium, Silver, Cadmium, Indium, Tin, Antimony, Tellerium, Iodine, Xenon, Cesium, Barium, Lanthanum, Cerium, Praseodynium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Hafnium, Tantalum, Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold, Mercury, Thallium, Lead, Bismuth, Polonium, Astatine, Radon, Francium, Radium, Actinium, Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium, Rutherfordium, Dubnium, Seaborgium, Bohrium, Hassium, Meitnerium, Darmstadtium, Roentgenium, Cpernicium, Ununtrium, Ununquadium, Ununpentium, Ununhexium, Ununseptium and Ununoctium.

List of all metals:

Lithium, Berlillium, Sodium, Magnesium, Aluminum, Potassium, Calcium, Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Nickel, Copper, Zinc, Gallium, Rubidium, Strontium, Yttrium, Zirconium, Niobium, Mollybdenum, Telerium, Rutherfordium, Rhodium, Palladium, Silver, Cadmium, Indium, Tin, Cesium, Barium, Lanthanum, Cerium, Praseodynium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Hafnium, Tantalum, Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold, Mercury, Thallium, Lead, Bismuth, Francium, Radium, Actinium, Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium, Rutherfordium, Dubnium, Seaborgium, Bohrium, Hassium, Meitnerium, Darmstadtium, Roentgenium, Cpernicium, Ununtrium, Ununquadium, Ununpentium, Ununhexium, Ununseptium and Ununoctium.

List of all non metals:

Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Florine, Neon, Phosphorus, Sulfur, Chlorine, Argon, Selenium, Bromine, Krypton, Iodine, Xenon, Astatine and Radon.

List of all transition elements:

Scandium, Titanium, Vandium, Chromium, Manganese, Iron, Cobalt, Nickel, COpper, Zinc, Yttrium, Zirconium, Niobium, Molybdenum, Technetium, Ruthenium, Rhodium, Palladium, Silver, Cadmium, Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Hafnium, Tantalum, Tungsten, Rhenium, Osmium, Iridium, Platinium, Gold, Mercury, Actinium, Thorium, Protactinium, Uranium, Neptunium, Plotonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium, Rutherfordium, Dubnium, Seaborgium, Bohrium, Hassium, Meitnerium, Darmstadtium, Roentgenium and Copernicium.

List of inner transition elements:

Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Actinium, Thorium, Protactinium, Uranium, Neptunium, Plotonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium.

List of metalloid (semi-metals):

Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Polonium.

List of representative (main group) elements:

Hydrogen, Helium, Lithium, Berillium, Boron, Carbon, Nitrogen, Oxygen, Florine, Neon, Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulfur, Chlorine, Argon, Potassium, Calcium, Gallium, Germanium, Arsenic, Selenium, Bromine, Krypton, Rubidium, Strontium, Indium, Tin, Antimony, Tellurium, Iodine, Xenon, Cesium, Barium, Thallium, Lead, Bismuth, Polonuim, Astatine, Radon, Francium and Radium.

List of alkali metals (group 1 elements):

Hydrogen, Lithium, Sodium, Potassium, Rubidium, Cesium and Francium.

List of alkaline earth metals (group 2 elements):

Beryllium, Magnesium, Calcium, Strontium, Barium and Radon.

List of halogens (group 17 elements):

Florine, Chlorine, Bromine, Iodine and Astatine.

List of noble gases (zero group elements or 18th group elements) :

Helium, Neon, Argon, Krypton, Xenon and Radon.

List of Lanthanide series elements:

Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium and Lutetium.

List of Actinide series elements:

Actinium, Thorium, Protactinium, Uranium, Neptunium, Plotonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium and Lawrencium.

Why do the last 18 elements in the periodic table have names starting with Un... ?

2010-12-28T06:45:00.000-08:00

A series of elements present at the end of the Periodic Table have names that start with the two letters Un... These elements are:

Name of element	Atomic number
Unnilunium	101
Unnilbium	102
Unniltrium	103
Unnilquadium	104
Unnilpentium	105
Unnilhexium	106
Unnilseptium	107
Unniloctium	108
Unnilennium	109
Ununillium	110
Unununnium	111
Ununbium	112
Ununtrium	113
Ununquadium	114
Ununpentium	115
Ununhexium	116
Ununseptium	117
Ununoctium	118

Why do these elements all start with Un.. ?

All these elements starting with Un... have atomic number greater than 100. These elements cannot occur naturally. They can only be obtained by the artificial transmutation of elements.

Each of these elements were discovered by many scientists worldwide. It has not been confirmed who discovered them first. Since all the scientists who discover an element name it according to them, the names of these elements could not be established as their discovery is yet controversial. For example, the element with atomic number 104 (Unnilquadium) was only recently discovered by both American and Soviet scientists. The American scientists called it "Rutherfordium" but the Soviet scientists called it "Kurchavotium".

In order to avoid confusion, the IUPAC (International Union of Pure and Applied Chemistry) has decided that these elements should be named according to a set of rules until their discovery is confirmed.

The set of rules, or the naming convention for these elements are as follows:

Rules for the name of the element

Each element will be named by the use of "roots" according to the atomic number of the element. Each "root" will denote a particular number as follows:

Number:	0	1	2	3	4	5	6	7	8	9
Root:	nil	un	bi	tri	quad	pent	hex	sept	oct	enn

For example, the fourth element with atomic number 104 will be named as follows:

From the digits 104,

1 is for "un"
0 is for "nil"
4 is for "quad"

So we get "unnilquad"

The first letter will be made capital, so we get "Unnilquad"
Each element's name will be followed by "ium", so we get "Unnilquadium".

Rules for the symbol of the element

The symbol for the element will be the first letters of each of the roots used in its name.
For example, the roots used in the name of Unnilquadium are un, nil and qaud. Taking the first letter of each of these roots, we get "unq".
The first letter of the symbol obtained above will be made capital. So we get "Unq".
Therefore the symbol for element Unnilquadium with atomic number 104 is "Unq".

Special conditions in naming

Sometimes special conditions arise in the above naming convention. These are as follows:

If enn occurs before nil, the second n of enn will be dropped.
If bi occurs before ium, the i of bi should be dropped.
If tri occurs before ium, the i of tri should be dropped.

What are representative elements in the periodic table?

2010-12-27T13:39:00.000-08:00

The representative elements are all the elements in groups one, two, thirteen, fourteen, fifteen, sixteen, seventeen and eighteen of the periodic table.

The representative elements in the periodic table do not exhibit variable valencies.
These include metals, non metals and semi metals (metalloid).
The metals are present in the left groups of the representative elements, while the non metals are present in the right most groups and the semi metals (metalloid) are present in the middle in a the shape of a zig zag line that separates the metals from the non metals.
These elements are also called the main group elements of the periodic table.
There are a total of 44 elements in representative elements. These include the Alkali metals, the Alkaline earth metals, the Halogens, the Nitrogen family, the Carbon family of elements, the Oxygen family of elements, the Boron family of elements and the noble gases present at the far right group.
The main group elements form the S and P blocks of the periodic table.
These elements are the most abundant elements on the earth.

All the representative elements' groups were sub categorized as group I-A to group VII-A of in the periodic table in the older naming convention. In this naming system, group I-A means the alkali metals, and group VII-A means the halogens. The noble gases are known as group zero elements. See here: How are groups named in the periodic table?
Here is a list of all representative elements in the periodic table.

What are the two rows placed at the bottom of the periodic table?

2010-12-27T13:21:00.000-08:00

The two rows present at the bottom of the periodic table together form the Inner Transition elements of the periodic table. The inner transition elements in the periodic table are a part of the transition metals, which range from the third to the twelfth group of the periodic table. The two rows placed at the bottom of the periodic table are the two series of elements, the Lanthanide series and the Actinide series.

Lanthanide series
The elements in the upper row form the Lanthanide series of elements, since the first element in the row is Lanthanum. Lanthanum is placed in the third group in the sixth column of the periodic table. It is the first element of the Lanthanide series, and the rest of the elements are present in the first row at the bottom of the periodic table.

Actinide series
The elements in the lower row form the Actinide series of elements. They are named so, because the first element of this series is Actinium. This element is placed in the third group in the seventh row of the periodic table. The rest of the elements of the Actinide series are placed in the second row at the bottom of the periodic table.

Why are the two rows placed at the bottom of the periodic table?
The two rows of elements are placed at the bottom of the periodic table in order to not distort th shape of the periodic table. These elements are more than what can be placed in a single row in the periodic table. If they would be placed in the periodic table, this would cause the shape of the periodic table to become highly distorted. This is because all the elements in each of the two rows belong to one particular group - the elements of the first row, that is the Lanthanide series elements, belong to the third group of the periodic table, and so do the elements of Actinide series.

Important points about the elements in the two rows at the bottom of the periodic table.

These elements are combined known as the Rare earth metals along with the two more element present in their group - Scandium and Yttrium.
These elements are all radioactive in nature. See here : "What are radioactive elements?"
These elements all belong to the third group of the periodic table.
These elements are called the Inner Transition elements, or the Inner Transition metals.

What are radioactive elements on the periodic table?

2010-12-27T12:59:00.000-08:00

Definition of radioactive elements:
Radioactive elements are those elements whose atoms have an unstable nucleus as a result of which they emit certian electromagnetic radiations like Alpha, Beta and Gamma radiations.

Explanation of radioactive elements:

Radio active elements emit radiations like Alpha, Beta and Gamma radiations.

Alpha, Beta and Gamma radiations are a type of electromagnetic waves, like visible light. The atoms of radioactive elements in their natural state emit these radiations.

The nucleus of the atoms of radioactive elements is unstable

The nucleus in any atom contains protons and neutrons. The number of neutrons is generally equal to the number of protons for any element. But there are elements in which the number of neutrons per nucleus is greater than the number of protons. This causes the nucleus of those elements to become unstable. It tries to lose the extra mass so that the number of neutrons becomes equal to the number of protons.
For losing the extra mass, the nucleus of the element starts emitting its subatomic particles, that is, neutrons, protons, and electrons in the form of electromagnetic radiations known as Gamma, Alpha and Beta radiations.

Position of radioactive elements in the periodic table
Radioactive elements have an unstable nucleus. The number of neutrons in the nuclei of radioactive elements is larger than the number of protons. This occurs generally in elements that have a large atomic mass. The elements having larger atomic masses are present in the lower rows of the periodic table. In general, all elements after Lead (Pb) in the periodic table have an unstable nucleus, and they all have high atomic masses.

The two rows at the bottom of the periodic table consist of radioactive elements. These are known as the rare earth metals. These are heavy metals since they have high atomic masses.
The first row elements are known as the Lanthanide series of elements, since their first element is Lanthanum. The second row of elements is known as the Actinide series of elements, since their first element is Actinium. These are all radioactive elements (rather metals).

Why are the two rows placed at the bottom of the periodic table? These are the elements that should come in the sixth and seventh rows of the periodic table. But representing them in their respectable rows would highly distort the shape of the periodic table. Therefore these elements are put in tow rows at the bottom of the periodic table, to maintain the shape of the periodic table.

How does electron affinity vary in the periodic table?

2010-12-06T11:29:00.000-08:00

Electron affinity definition

Electron affinity is a measure of the energy released when an electron is added to an atom to form a negative ion. A positive electron affinity denotes that an atom accepts electrons easily, and thus is a nonmetallic/electronegative atom. A negative electron affinity denotes that the atom does not accept electrons (furthermore it loses them), and it is a metallic/electropositive element.

Factors on which electron affinity is dependent:

Atomic size : Electron affinity decreases with increase in atomic size.
Reason: The lesser is the atomic size, the lesser is the distance between the nucleus and the outermost electron shell. This means that the positive charge in the nucleus holds the outermost electrons more firmly and thus makes the atom an electron acceptor. Thus, the electron affinity is increased.
Nuclear charge (atomic number) : Electron affinity increases with increase in nuclear charge/atomic number.
Reason: The greater is the nuclear charge/atomic number, the greater is the attractive force of positive protons on negative electrons. Thus, the atom tends to gain electrons when its atomic size is greater.

Variation of electron affinity:

Across the rows of the periodic table: On moving from left to right in the periodic table, the electron affinity of the elements increases.
Reason: The atomic size gets smaller as we move across the rows of the periodic table from left to right, and the nuclear charge/atomic number also increases simultaneously. This causes the electron affinity of atoms to be increased tremendously. Thus, we find that, on moving from left to right in the periodic table, the elements become more non metallic and lesser metallic.

Down the groups of the periodic table, the electron affinity decreases.
Reason: the atomic size of elements decreases down the groups of the periodic table, but the atomic number increases. However, the effect of the decrease in atomic size outshines the effect of the decrease in atomic number. Thus, the attractive force of the nucleus on the outermost orbit electrons decreases, and hence the electron affinity of the elements decreases.

How does electronegativity vary on moving across the row and down the columns of the periodic table?

2010-12-05T07:32:00.001-08:00

What is electronegativity:

Electronegativity is a tendency. It shows us how much an element's atom attracts electrons towards itself. The more electronegative an element is, the more will it attract electrons towards itself. This means that an electronegative element is a non metallic element. It tends to gain electrons in order to form negative ions, and if not so, then it tries to attract the shared pair of electrons in a covalent bond towards itself.

Factors on which it is dependent

Electronegativity is dependent on the atomic number and the atomic size of an atom.

Atomic number: Increased atomic number increases electronegativity.
Reason: Electronegativity is the tendency of an atom to attract electrons towards itself. The more the atomic number will be, the more will be the positive charge in the nucleus, and therefore the more will the atom attract electrons towards itself.
Atomic size: Lesser the atomic size, the more is the electronegativity
Reason: Less atomic size means lesser distance between the nucleus and the outermost electron orbit. Thus the attractive force on the outermost shell will increase since it is closer to the positively charged protons in the nucleus. Hence the atom will attract electrons to come into its outermost orbit with more force, and this means that the electronegativity of the atom is more. Therefore the lesser the atomic size, the more electronegative an element is.

Variation of electronegativity

Across rows in the periodic table: Electronegativity increases as we move from left to right in the periodic table.
Reason: when one moves from left to right in a row of the periodic table, the atomic size of the elements decreases (this is explained in the post of atomic size), and the atomic number increases. Therefore the atoms of elements are able to attract electrons with more force. Therefore electronegativity increases.
Down the columns of the periodic table: Electronegativity decreases as we move from top to bottom in the periodic table.
Reason: When one goes from top to bottom in a group of the periodic table, the atomic size of elements increases but the atomic number also increases. The increase in atomic size is effective to a greater extent than the increase in atomic number, and hence the electronegativity of elements decreases down a group.

What are trends in the periodic table?

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Certain properties, such as electronegativity, show a regular similarity in the periodic table after regular intervals. They show patterns of gradual variation in the rows and columns of the periodic table. These properties are called the periodic properties, and this phenomenon is called the periodicity of elements, and commonly referred to as the periodic table trends.

What does periodicity of elements (aka periodic table trends) do?

Periodic table trends occur in the rows and columns of the periodic table. Elements in the periodic table show similarities in their properties (such as electronegativity) after regular intervals. This phenomenon, also known as the chemical periodicity, can be explained by the help of an example:

Electronegativity is a property of elements that indicates the non metallic nature of the elements. In the periodic table, the electronegativities of elements of the seventeenth group (the halogen family of elements) are all high, thus making all of these elements strong non metals. Furthermore, when we move across a row from left to right in the periodic table, the electronegativity of elements increases till the seventeenth group, and when we move down a group of the periodic table, the electronegativities of elements decreases till the 7^th row. Thus, we can see a regular repetition and gradual variation in the electronegativity of elements in the periodic table. This periodic trend is the phenomenon of periodicity of elements.

Apart from electronegativity, there are other periodic properties that follow the phenomenon of periodicity of elements in the periodic table. These properties are :

atomic size (atomic radius)
electronegativity
electron affinity
ionization energy

Trends of periodic properties in the periodic table are explained in following questions:

How does atomic size of elements vary in the periodic table?

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Atomic size definition:

This is the atomic radius. It is measured from the center of the atom to the outermost electron shell of the atom.

Factors on which atomic size is dependent:

The atomic size (or radius) of elements is dependent on the atomic number and the number of shells of the atoms of elements:

Atomic number: As the atomic number of elements increases, the atomic radius decreases. This is because the increase in atomic number means increase in the number of protons in the nucleus of the element. Increase in the number of protons means that the positive charge in the nucleus has also increased. The increase in the positive charge in the nucleus causes the outermost shell of electrons to be attracted towards it and thus the outermost shell is pulled towards the nucleus. This causes the decrease in the atomic radius of the atom.
Number of shells : As the number of shells of atoms increases, the atomic size increases since the distance between the outer most shell and the nucleus also increases.

Variation across rows and down groups:

On going from left to right in a row of the periodic table, the atomic radius of the elements decreases.
Reason and explanation:
The number of shells in the atoms of elements remains same, where as the atomic number increases one by one. Since the atomic number increases, the number of protons in the nucleus of that element also increases, and hence the attractive force between the outer electrons and the protons in the nucleus also increases. This causes a decreases in the atomic size of the elements, since the outermost shell is pulled closer to the nucleus by the increasing positive charge of the nucleus.
On going down a group of the periodic table, the atomic radius of elements increases
Reason and explanation:
On moving down a group of the periodic table, the number of shells in each elements atoms increases one by one with each element. This causes an increase in the atomic size of the elements as we go down a group in the periodic table. The atomic number of elements also increases as we move down a group, and that should reduce the size of the atoms, but the decrease in atomic size caused by the increase in atomic number is slight as compared to the increase caused by increasing number of shells. Therefore, the atomic size of elements decreases as we move down a group of the periodic table.

Who made the periodic table?

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The periodic table was made by the effort of many scientists, chemists and physicists worldwide over a time period of many decades. It was made in order to arrange the elements in accordance with their chemical and physical properties.

It was Dmitri Mendeleev, in 1869, who made the periodic table we use today. His periodic table was the first one that was appropriate enough to be accepted as the official periodic table at that time. The arrangement of elements in it was such that it even allowed Mendeleev to predict the existence of yet undiscovered elements at that time, like putting the parts of a jigsaw puzzle together.

There was, however, a major anomaly in his periodic table, and that was the placement of isotopes. Isotopes are the atoms of the same element that have same atomic numbers but different atomic masses. Since Mendeleev's periodic table was arranged in increasing order of the atomic masses of elements, therefore the positioning of isotopes became a major issue in it. This defect was corrected in 1920 by Henry Moseley, who rearranged Mendeleev's periodic table by ordering the elements in increasing order of their atomic numbers rather than their atomic masses. Since isotopes have same atomic numbers, this periodic table did not have any fall-backs.

Thus, the current long form of the periodic table was established in 1920, but the credit of invention goes to Dmitri Mendeleev, since he was the one who made the basic structure of the current periodic table.

Other notable attempts to make the periodic table were of John Newland (in 1864/1865) and Doberiener (in 1829) in the Law of Octaves and the Law of Triads.

How are groups named in the periodic table?

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The groups in the periodic table are now numbered, not named, according to the latest recommendations of IUPAC.

They are numbered 1 to 18 from left to right in the periodic table, as there are 18 groups in the modern periodic table of elements. This is the new naming convention/system adopted by IUPAC. The older system of naming the groups has however, not lost its significance, and it should be learnt also.

The older naming system names the groups using Roman numerals and English alphabets 'A' and 'B'. The groups from left to right in the periodic table are named as follows:

IA, IIA, IIIB, IVB, VB, VIIB, VIIIB, IB, IIB, IIIA, IVA, VA, VIA, VIIA, VIII group.

The noticeable thing in the above naming system is that :

One, there are only 16 groups here. This is because the group named VIIIB contains three vertical columns (columns 8^th, 9^th and 10^th of the current periodic table) which makes a total of 18 columns.
There are two letters A and B used in this system. This is a was of classifying the elements. The letter A is used to represent the “Representative elements” and the letter B is used to represent the “Transition elements” of the periodic table.
The Roman numbers I and VIII occur in two groups, group A and group B. In each group, the roman number represents the total number of outer electrons present in the atoms of the element that falls into that group.

The newer system numbers the groups from 1 to 18 from left to right. Group 1 is the alkali metals group, group 2 is the alkali earth metals group, and group 18 is the noble gases group, group 15 the nitrogen family, and so on.

What are the horizontal rows in the periodic table?

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The horizontal rows in the periodic table are called “Periods”. There are 7 such rows in the periodic table. All elements having the same number of electron shells in their atoms are placed in each row of the periodic table. This leads to a gradual variation

There are two elements in the first row of the periodic table. There are 8 elements each in the second and the third rows, 18 elements each in the fourth and the fifth row, 32 elements in the sixth row, and the 7^th row is considered an incomplete row, because newly discovered elements are added to it. The sixth and seventh rows of the periodic table contain the elements that are shown in two rows beneath the periodic table, namely, the Lanthanide and the Actinide series.

The rows in the periodic table show a gradual variation of characteristics. This is a part of the phenomenon called the “Periodicity of properties in the periodic table.” The rows contain elements of increasing atomic numbers (and, consequently, atomic weights) from left to right. Properties like atomic size, metallic character, electron affinity, electronegativity and ionization potential show gradual variation in the rows of the periodic table.

The row number of an element in the periodic table indicates the number of electron shells present in the atoms of that element. This helps in determination of electronic configuration of an element from its position in the periodic table. For example, the first row elements, Hydrogen (H) and Helium (He), contain 1 shell in their atoms, the second row elements, Lithium (Li) to Neon (Ne), contain 2 electron shells in their atoms respectively.

What are the vertical columns in the periodic table?

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The vertical columns in the periodic table are called “Groups”. There are eighteen groups in the periodic table.

Naming of these groups

The groups in the periodic table are numbered 1 to 18 according to the latest recommendations of IUPAC. However, the older system of naming the groups is still important enough to be remembered. In the old system, the groups were named as follows:

IA, IIA, IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIB, IVA, VA, VIIA, VIII group

As you may notice, there are only 16 groups in the above system. This is because the group VIIIB contains three vertical columns which are the 8^th, 9^th and 10^th columns according to the current naming system. The old system of naming of the groups is significant because it denotes the number of electrons present in the outer shell of the atoms of the elements present in that group. For example, group IA elements have 1 electron in their outer shells, and group VIIA elements have 7 electrons in their outer shells.

Characteristics of groups (vertical columns) in the periodic table

All elements present in the same group of the periodic table contain the same number of valence electrons. As a result, their chemical properties are similar and they show a gradual variation of many characteristics when going down a group.
For example, the alkali metals in the first group of the periodic table all have 1 valence electron. Their chemical properties are also similar. They react with water to liberate hydrogen gas and to produce their respective hydroxides.

Groups are also referred to by some common names in the periodic table. These are alkali metals (the first group), alkali earth metals (the second group), halogens (the third group), etc.

The group containing the most number of elements in the periodic table is the third group, as it contains the Lanthanide and the Actinide series of elements, each of which are a group of 15 elements. These two series of elements are placed at the bottom of the periodic table in order to not distort its shape.

Why do we have a periodic table?

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Simply, the periodic table helps us to keep all known elements arranged in order. There are a hundred and eighteen elements discovered so far. Every element has a different set of chemical and physical properties. There are similarities in chemical and physical properties of many elements. There is a need to classify the elements properly so that we study all elements in an orderly fashion.

The periodic table contains elements arranged in increasing order of their atomic numbers. There are seven rows and eighteen columns in the periodic table. The rows are known as periods and the columns are known as groups. The periodic table is arranged such that there is a distinct variation of physical and chemical properties visible on it in the rows and columns. This makes it more useful as a source of classified information of elements.

The current periodic table was made by Dmitri Mendeleev in 1869. It was later on corrected by Henry Moseley in 1920. Before that there were many attempts made to classify the elements. Some of the notable attempts were the “Law of Octaves” by John Newland and “Law of Triads” by Doberiener. These all attempts were different methods used to classify elements. They aimed at arranging elements in a way that was most efficient and error free. However, each method had some errors that were not acceptable. So the attempts continued for decades until the modern periodic table was made by Dmitri Mendeleev and corrected by Henry Moseley.

The periodic table helps us to find the general properties of elements at a glance. It contains the atomic number, the atomic mass, and the symbol of elements. By looking at the position of an element in the periodic table, we are able to tell its physical and chemical characteristics to a high degree of accuracy. For example, all elements present in the first group will be metals, reactive elements, and will form ionic bonds with non metallic elements resulting in the formation of ionic compounds. They will be good conductors of electricity, and on dissolving them in water we will obtain their alkali and hydrogen gas.

Similarly, the elements of the seventeenth group of the periodic table will be nonmetals, reactive elements. They will form negative ions by gaining electrons, and they will react with metals to form ionic compounds.

Thus, we are able to guess the general chemical nature of an element from its position in the periodic table.

What does a periodic table have on it?

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Elements. The periodic table has elements on it. Elements are arranged in the periodic table in rows and columns. The elements are arranged in the periodic table in the increasing order of their atomic numbers.

What are elements?

Elements are pure substances. They are made up of only one type of particles (atoms) throughout. There are 118 elements discovered till today. The elements make up all things in nature. They combine to form compounds, and all rocks, soils, air, water, are all made up of elements and compounds.

There are many different types of elements based on their physical states, chemical reactivity, and chemical properties. The most common classification of elements is metals, non metals, and metalloids (or semimetals). Metals are the elements like iron, gold, silver etc. Non metals are elements like oxygen, nitrogen, sulfur, carbon (like graphite and diamond), etc,

Since there are so many elements, so many types of elements, and so many chemical and physical properties of atoms of those elements, that it is essential for scientists, physicists, and chemists world over to be able to study, classify, organize and view all elements in a uniform way. Therefore elements are arranged in a table of elements, known as the periodic table of elements. Thus arises the need of a periodic table. A periodic table is used to arrange the elements so that they are in an orderly fashion and they are classified properly.

The periodic table is arranged in the increasing order of the atomic numbers of elements. It has seven rows and eighteen columns. Elements from left to right in each row have increasing atomic numbers by 1. At the end of each row, elements are arranged from left to right in the next row. In the first row of the periodic table, there are 2 elements, in the second and third row, there are 8 elements each; in the fourth and fifth row 18 elements each, and in the 6^th and 7^th rows, there are 32 elements each. The 7^th row is considered to be an incomplete row, since newly discovered elements are added in it continuously.

There are two types of elements, one is the elements than occur naturally, and the other is the elements that are synthesized artificially. The artificially synthesized elements are not found in nature, but are made by people in the laboratory after a lot of work. These elements are generally the byproducts of radioactive elements.

What is the periodic table?

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The periodic table is an arrangement of elements in rows and columns. It is a table of elements.. At each intersection of a row and a column, one element is placed. There are a total of 118 different elements in the periodic table.

There are 7 rows and 18 vertical columns in the periodic table. The rows are called the periods in the periodic table and the columns are called the groups in the periodic table.

Elements are arranged in increasing order of their atomic numbers in the periodic table. This means that the first element has atomic number of 1 and the successive elements have atomic numbers 2, 3, 4, and so on.

The periodic table was made in order to arrange all known elements in a proper order, so that scientists worldwide can refer to it and not be confused by one anothers references. The periodic table was made in order to study the elements properties in an orderly way, and to avoid chaos in studying the properties of elements.

The periodic table helps us to remember all the elements. It classifies elements on the basis of their properties. For example, the metals are placed on the left and the middle of the periodic table, the non metals are placed on the extreme right of the periodic table, whereas the metalloids (semi-metals) are placed in the middle of the metals and the non metals in a zig-zag line in the periodic table.

So, to summarize it, the periodic table is a table of elements arranged in ascending order of their atomic numbers in rows and columns such that elements with the same chemical properties get huddled together in a group in the periodic table.
This is because the periodic table is arranged in the increasing order of the atomic number of elements, and the periodic law states that “The physical and chemical properties of elements are periodic functions of their atomic numbers”

Why periodic table is known as periodic table?

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The word periodic means regular. It relates to the periodic table of elements in the following different ways:

The periodic table is known as the periodic table because it is based on the periodic law and because it is arranged so that the elements show periodicity of properties in it.

The horizontal rows in the periodic table are called the periods of the periodic table.

The periodic law says that "the physical and chemical properties of elements are the periodic functions of their atomic numbers." The modern periodic table is based on this law. That is why the periodic table is called periodic. In simple words, the periodic law means that when elements are arranged in ascending order of their atomic numbers, they show similarities in properties after regular intervals.

The phenomenon called periodicity of properties occurs in the modern periodic table. This is related to the above mentioned periodic law. In this phenomenon, the elements as arranged currently in the periodic table show similarities in their properties after regular intervals in the periodic table. These periodic properties also show a gradual variation in groups and rows of the periodic table. They are called the trends in the periodic table.

The periodic properties repeat themselves in the periodic table after regular intervals. These periodic properties are atomic size, ionization potential, electro-negativity, electron affinity, etc. These properties vary across rows and columns of the periodic table.

For example, the atomic size of elements decreases as we move from left to right across rows in the periodic table. This is because the number of shells remains same throughout each row of the periodic table whereas the atomic number increases. Due to this the attraction of the protons in the nucleus on the outer electrons of the atoms increases and therefore the outer shells come closer to the nucleus. Thus, the atomic size of elements atoms decreases as we move from left to right across a row of the periodic table.

Thus, the periodic table is called periodic because of the phenomenon of periodicity of properties in which certain properties of elements, called periodic properties, repeat themselves periodically throughout the periodic table.