Important Terms of Chemistry

Important Terms of Chemistry

(a) Metals : Metals comprise 75% of all known elements and appear on the left hand side of the periodic table.

Metals are solids at room temperature (except mercury, gallium and francium).

They are malleable, ductile and good conductors of heat and electricity.

(b) Non – Metals : These can be gases, liquids or even solids with low m.p and b.p. Most of them are brittle and are neither malleable nor ductile.

(c) Metalloids : The elements which show the properties of both metals and non – metals are known as metalloids or semi – metals.

(d) Valency :

• The valency of a metal is equal to number of valence electrons. The electrons present in outer- most orbit are called valence electrons. (or)
• Valency is equal to the number of hydrogen atoms or twice the number of oxygen atoms which combines with one atom of an elements. (or)
• The valency of a non – metal elements is usually equal to eight minus the number of valence electrons in its atom.
• The atoms combine with each other since; they have a tendency to acquire eight electrons (except hydrogen atom) in its outermost orbit. The atoms which give outermost electrons acquires positive charge and other which take electrons acquire negative charge.

(e) Atomic Radius : The distance between the centre of nucleus and the outer most shell of electrons.
(f) Van der Waal’s Radius : Half of the distance between the nuclei of two adjacent atoms belonging to two neighbouring molecules of an element.
(g) Ionic Radius : The distance from the nucleus of an ion up to which it has influence on its electron cloud.
(h) Ionization energy (Ionization potential or Ionization enthalpy) : The minimum amount of energy required to remove an electron from an atom.
The ionization energies required to remove first second and third etc., electrons from an atom are called successive ionization energies.
Remember that Third IE > Second IE > First IE
Ionization energy is governed by the factors :

• Nuclear Charge : Energy increases with increase in nuclear charge
• Atomic Size : Energy decreases with increase in size
• Penetration effect of the Electrons : Energy increases with increase in penetration effect
• Screening effect of the Inner Shell Electrons : Energy decreases with increase of screening or shielding effect
• Effect of half – filled or completely filled Orbitals : If an atom contains half – filled or completely filled orbitals then it is more stable, so the energy required is more than expected.