Chemical Properties and Periodicity:-

(1) Valency:- (a) It is the combining capacity  of an element.

 (b) It is either equal to the number of valence electron or (8 – number of Valence electrons).

Trend of valency Along the groups / periods.

Periods	Groups
Trend:- Trom left to right valency increases from 1 to 4 than decreases to O.	In top to bottom valency remains same because of similar number of valence electrons. example- Alkaline Metals have 2 valency

 

Write down the compound formed between following pairs?

(a) Mg⁺² and N^3-           Mg₃N₂

(b) Element 7I and F     CuF₃

(c) Si and S                         Si S₂

(d) Si⁺⁴ and O^2-                      Si O₂ or Si₂ O₄

(e) Ca⁺² and O^2-               Ca O

(2) Diagonal Relationship (DR):- It is the similarity in propect of elements of second period and third period placed drag only in periodic table.

Cause of Diagonal Relationship:- Similar ionic size

(b) Similar polarizing power Ionization energy charge / size ratio.

Ionization energy tendency to attract the electron cloud of anion by a cation in ionic bind.

Important points:-

(a) In a periodic table more than 75% are metals these are normally placed on left hand side of the periodic table.

(b) Transition from metallic to non-metallic behavior is not abrupt Via semi-metals or metalloids example:- Si, Te.

(c) Group 17) Ionisation energy halogens has metals, non-metals, gases, liquid, solids.

(d) In case of metals reactivity increases from top to bottom and Ionisation Energy decreases and Metals Reducing character increases from top to bottom

(e) In case of non-metals (halogens) reactivity decreases from top to bottom and electron gain enthalpy less negative.