VALENCY, OXIDATION NUMBER, IONS AND RADICALS

VALENCY

The valency of an element is the combining power of the element. It is defined as the number of atoms of hydrogen that will combine with or displace one atom of the element in chemical reactions. Some elements have more than one valency. For example.

First twenty elements with their valencies show this character.

EVALUATION:

1. What do you understand by the word chemical symbol?
2. Define valency of an element.

OXIDATION NUMBER OF ELEMENTS

To be able to write correctly chemical formulae for compounds, a system of small whole numbers, related to the combining ratio of element has been developed on the basis of arbitrary rules. Such numbers are called oxidation numbers or oxidation states.

Rules for Assigning Oxidation Number

1. The ON of an uncombined free element, whether monoatomic or polyatomic is zero; e.g. Noble gases (He, Ne, etc), metals (Na, Zn, etc),solid non-metals (O₃, N₂, F₂,etc)
2. The oxidation number of a monoatomic ion is equal in magnitude and sign to its ionic charge; e.g., the ON of bromide ion, Br^-1, is -1; that of F⁺³, is +3.