a) H₂S:

The atomic number of S is 16 and the no. of valence electrons is 6. The atomic number of H is 1 and no. of valence electron is 1. Hence, the total number of valence electrons is:

Two hydrogens (2× 1 valence electron) + sulphur (6 valence electrons) = Total 8 valence electrons

[Each line represents a pair of electrons]

The central atom S shares its two valence electrons out of six valence electrons to complete its octet and each hydrogen atom shares its one valence electron to complete the octet. The remaining four electrons act as a lone pair (electrons which do not participate in bonding) which is placed on the sulphur atom.

b) SiCl₄

The atomic number of Si is 14 and the no. of valence electrons is 4. The atomic number of Cl is 17 and no. of valence electron is 7. Hence, the total number of valence electrons is:

Four chlorines (4× 7 valence electrons) + silicon (4 valence electrons) = Total 32 valence electrons

The central atom Si shares it’s all valence electrons and each chlorine atom shares its one valence electron out of seven valence electrons to complete the octet.

c) BeF₂:

The atomic number of Be is 4 and the no. of valence electrons is 2. The atomic number of F is 9 and no. of valence electron is 7. Hence, the total number of valence electrons is:

Four fluorine (4× 7 valence electrons) + Beryllium (2 valence electrons) = Total 30 valence electrons

The central atom Be shares its all valence electrons and each fluorine atom shares its one valence electron out of seven valence electrons to complete the octet.

d) CO₃^2-

The atomic number of C is 6 and the no. of valence electrons is 4. The atomic number of O is 8 and no. of valence electron is 6. Hence, the total number of valence electrons is:

Three oxygen (3× 6 valence electrons) + Carbon (4 valence electrons) + negative charge (2 extra electrons) = Total 24 valence electrons

The central atom C shares its all valence electrons with each oxygen atom. Carbon requires only two electrons to complete its octet hence, only one of the oxygen atom shares its two valence electrons out of six valence electrons which are represented by a double bond.

e) HCOOH:

The atomic number of C is 6 and the no. of valence electrons is 4. The atomic number of O is 8 and no. of valence electron is 6.

The atomic number of hydrogen is 1 and no. of valence electron is 1. Hence, the total number of valence electrons is:

two oxygen (2× 6 valence electrons) + Carbon (4 valence electrons) + two hydrogen (2 × 1 valence electron) = Total 18 valence electrons

The central carbon atom shares it’s all 6 valence electrons with one hydrogen and two oxygen atoms to complete its octet. One of the oxygen atoms shares its two valence electrons with carbon which is represented by a double bond.