# Quiz 1 | Lewis Formulas

1

How many covalent bonds should form a neutral oxygen atom to follow the octet rule?

1

2

3

4

Electronic configuration of O (Z = 8): 1s2 2s2 2p4 ⇒ 6 valence electrons

A neutral oxygen atom needs 2 more electrons to follow the octet rule

2

What type of bond exists between the nitrogen atoms of N2H2?

Single bond

Double bond

Triple bond

3

Which of the following species has a triple covalent bond?

NH3

CO2

NO3-

NC-

4

What is the formal charge of boron atom in the molecule BF4-?

-2

-1

0

1

nb of valence electrons in a free boron atom: 3

nb of valence electrons in the bound boron atom of BF4-: 4

Formal charge = 3 – 4 = -1

5

Which of the following atoms could have an expanded valence shell?

Li

O

S

Ne

Valence shell of Li, O and Ne: n =2

Valence shell of S: n = 3

Expanded valence shell can happen only for atoms with a valence shell n $\ge$ 3

6

Which of the following atoms has the highest electronegativity?

F

O

H

Br

Electronegativity increases across a period and towards the top of a group in the periodic table