$\text{Number of electron groups} = \text{number of bonded atoms} + \text{number of lone pairs}$

Question 1

Which of the following statements best explains why hydrogen cannot be the central atom in a Lewis structure?

Accepted Answer

Hydrogen can only form one bond due to having only one valence electron.

Question 2

Given the Lewis structure for NF$_3$, how many lone pairs are present on the central atom?

Accepted Answer

1

Question 3

What is the molecular geometry and bond angle of CSH$_2$ according to its Lewis structure?

Accepted Answer

Trigonal planar, $120^	ext{o}$

Question 4

Which of the following molecules is polar based on its Lewis structure and molecular geometry?

Accepted Answer

NF$_3$

Question 5

A molecule has 4 electron groups around the central atom, with 2 bonded atoms and 2 lone pairs. What is its molecular geometry and bond angle?

Accepted Answer

Bent, $109.5^	ext{o}$

Question 6

Which rule is used to determine the number of electron groups around a central atom in a Lewis structure?

Accepted Answer

Number of electron groups = number of bonded atoms + number of lone pairs

Question 7

Why can't halogens (group 17 elements) be central atoms in Lewis structures?

Accepted Answer

They only form one bond due to having seven valence electrons.

Question 8

Which of the following best describes a molecule whose central atom has no lone pairs and is bonded to different types of atoms?

Accepted Answer

The molecule is polar.

Question 9

For SiH$_2$I$_2$, what is the electron group geometry and molecular geometry around the silicon atom?

Accepted Answer

Tetrahedral electron group geometry, tetrahedral molecular geometry

Question 10

A molecule has 3 bonded atoms and 1 lone pair around the central atom. What is its molecular geometry?

Accepted Answer

Trigonal pyramidal

Question 11

Which of the following molecules is nonpolar?

Accepted Answer

A molecule containing only C and H atoms

Question 12

What is the correct Lewis structure for NF$_3$?

Accepted Answer

N atom in center, three single bonds to F atoms, and one lone pair on N

Question 13

Which step is NOT part of the standard procedure for drawing a Lewis structure?

Accepted Answer

Assigning formal charges to all atoms before drawing bonds

Question 14

A molecule has 4 electron groups around the central atom, all of which are bonded atoms. What is its molecular geometry and bond angle?

Accepted Answer

Tetrahedral, $109.5^	ext{o}$

Question 15

Which of the following best describes the polarity of SiH$_2$I$_2$?

Accepted Answer

It is a polar molecule because the central atom is bonded to different types of atoms.

Question 16

Which of the following is the correct formula to determine the number of electron groups around a central atom?

Accepted Answer

$	ext{Number of electron groups} = 	ext{number of bonded atoms} + 	ext{number of lone pairs}$

Question 17

Which molecule would have a bond angle of $180^	ext{o}$?

Accepted Answer

A molecule with 2 electron groups and no lone pairs on the central atom

Question 18

Which of the following is true about the orientation of atoms in Lewis structures?

Accepted Answer

The orientation of atoms in Lewis structures does not affect the validity of the structure.

Question 19

A molecule has a central atom with one lone pair and is bonded to three other atoms. What is the expected bond angle?

Accepted Answer

$109.5^	ext{o}$

Lewis Structures, Molecular Geometry, and Polarity of Small Covalent Molecules

Study Guide - Practice Questions