2. Periodic Classification of Elements

a. The period with electrons in the shells K, L and M: 29

Third Period

b. The group with valency zero: 16

Group 0 or Group 18

c. The family of nonmetals having valency one: 29

Halogens
[Fluorine (₉F), Chlorine (₁₇Cl), Bromine (₃₅Br), Iodine (₅₃I), Astatine (₈₅At)]

d. The family of metals having valency one: 29

Alkali Metals
[Lithium (₃Li), Sodium (₁₁Na), Potassium (₁₉K), Rubidium (₃₇Rb), Cesium (₅₅Cs), Francium (₈₇Fr)]

e. The family of metals having valency two: 29

Alkaline Earth Metals
[Beryllium (₄Be), Magnesium (₁₂Mg), Calcium (₂₀Ca), Strontium (₃₈Sr), Barium (₅₆Ba), Radium (₈₈Ra)]

f. The metalloids in the second and third periods: 29

Second Period: Boron (₅B)
Third Period: Silicon (₁₄Si)

g. Nonmetals in the third period: 29

Phosphorous (₁₅P), Chlorine (₁₇C) and Sulphur (₁₆S)

h. Two elements having valency 4: 29

Carbon (₆C), Silicon (₁₄Si)