Introduction: Periodic Classification of Element

• Important data on Modern Periodic Table-

• Isotopes are placed at one place in the same group.

• There is no element between hydrogen and helium as atomic masses always comes in whole numbers.

• Atomic number is represented by Z, and it is equal to the number of protons in the nucleus of the atom.

• It also consists of 18 vertical columns known as Groups and 7 horizontal rows known as Periods.

• Elements having same number of valence electrons are placed in the same group.

• As we go down in a group, number of shell increases.

• Elements having same number of occupied shells are placed in same period.

• Each period has a new electronic shell getting filled.

• Number of elements placed in a particular period depends on the point how electrons are filled into various shell.

• To find out the number of electrons in a shell, 2n² formula can be used, where is n is shell number.

K Shell n = 1 or 2n² = 2(1)² = 2

L shell n = 2 or 2n² = 2(2)² = 8

• Valence electron also determines the number of bonds which is formed by an element.

• Valency and Valence Electrons –
  On moving left to right in a period, valency increases and then it decreases. But it remains same down in a group.
  
  As we move from left to right in a period, valence electron increases and remain same as we go down the group.

• Atomic Size –
  It decreases left to right in a period as the nuclear charge increases due to large positive charges on the nucleus.
  
  Atomic size increases down in a group due to decrease in nuclear charges and addition of new shell.

• Metallic Character –
  Ability of atom to lose the electron is known as Metallic Character. Metallic character decreases from left to right in a period.
  
  This is due to increase in nuclear charge. But non-metallic character increases left to right in a period. And metallic character increases down the group as the size increases it can easily lose electron.

Groups in Modern Periodic Table-

The modern periodic table contains 18 vertical columns known as groups.

Group 1 elements are known as alkali metals.
Group 2 elements are known as alkaline earth metals.
Group 15 elements are known as pnicogens.
Group 16 elements are known as chalcogens.
Group 17 elements are known as halogens.
Group 18  elements are known as noble gases.

Alkali Metals-

The elements in the first group, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr) are called alkali metals.
They were given the name because they all react with water to form alkalis.

The alkali metals are all shiny, soft, highly reactive solids at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1.
Number of valence electrons = 1

Alkali Earth Metals-

The elements in the second group, beryllium(Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) are called alkaline earth metals.

They were given the name because their oxides are alkaline in nature.

They are all shiny, silvery-white, somewhat reactive hard solids at standard temperature and pressure. They lose two electrons from their outermost shell to form cations with charge +2.

Number of valence electrons = 2

Halogens-

The elements in the seventeenth group (F, Cl, Br, I and As) are called halogens and exist as diatomic molecules. The symbol ‘X’ is often used generically to refer to any halogen.

They were given the name halogen, from the Greek words, Hal (“salt”) and gen (“to produce”), because they all produce a wide range of salts on reacting with metals.

The halogens exist at room temperature in all three states of matter: Solid – Iodine, Astatine. Liquid – Bromine. Gas – Fluorine, Chlorine.

Number of valence electrons = 7

Noble Gases-

The elements in the eighteenth group, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn) are called noble gases.

They are all odourless, colourless and monatomic gases with very low chemical reactivity.

Since their valence shell is considered to be “full”, they have little tendency to participate in chemical reactions.

When discovered and identified, scientists thought they are exceedingly rare, as well as chemically inert, and therefore these gases were also given the names ‘rare’ or ‘inert’ gases.

Number of valence electrons = 8

Classification of Modern Periodic Table-

Metals-

they are electropositive as they form bonds by losing electrons. In general cases, oxides of metals are basic in nature.

Non-metals-

Nonmetals are electronegative as they form bonds by gaining electrons. In general cases, oxides of non-metals are acidic in nature.

Metalloids-

The elements which show the properties of both metals and nonmetals are called metalloids or semimetals. For example – Boron, silicon, germanium, arsenic, antimony, tellurium and polonium.