$\text{Formal charge} = \text{number of valence electrons} - (\text{unshared electrons} + \frac{1}{2} \times \text{shared electrons})$

Question 1

Which of the following statements best describes a Lewis structure?

Accepted Answer

A molecular representation that shows both the connections among atoms and the locations of lone-pair valence electrons.

Question 2

When drawing the Lewis structure for $\mathrm{H_2S}$, how many lone pairs are present on the sulfur atom?

Accepted Answer

Two lone pairs

Question 3

Which atom is typically placed at the center of a Lewis structure for a molecule?

Accepted Answer

The atom that appears lowest or farthest to the left on the periodic table (except hydrogen)

Question 4

What is the formal charge on the central atom in $\mathrm{AlCl_3}$ according to its correct Lewis structure?

Accepted Answer

$0$

Question 5

Which molecule below contains a triple bond in its Lewis structure?

Accepted Answer

$\mathrm{N_2}$

Question 6

How many valence electrons are present in a molecule of $\mathrm{NH_3}$?

Accepted Answer

10

Question 7

Which of the following is an exception to the octet rule in Lewis structures?

Accepted Answer

$\mathrm{BF_3}$

Question 8

What is the correct Lewis structure for $\mathrm{CO_2}$?

Accepted Answer

O=C=O with each O atom having two lone pairs

Question 9

Which of the following best explains why hydrogen is never the central atom in a Lewis structure?

Accepted Answer

Hydrogen can only form one bond and achieve a duet, not an octet.

Question 10

In the Lewis structure for $\mathrm{C_2H_4}$ (ethylene), how many electrons are shared between the two carbon atoms?

Accepted Answer

4 electrons

Question 11

Which of the following steps is NOT part of the standard procedure for drawing Lewis structures?

Accepted Answer

Assign all electrons to the central atom before connecting ligands.

Question 12

What is the formal charge formula for an atom in a Lewis structure?

Accepted Answer

$	ext{Formal charge} = 	ext{number of valence electrons} - (	ext{unshared electrons} + \frac{1}{2} 	imes 	ext{shared electrons})$

Question 13

Which of the following molecules has a central atom that does NOT achieve an octet in its Lewis structure?

Accepted Answer

$\mathrm{AlCl_3}$

Question 14

If a central atom in a Lewis structure is in row 3 or higher of the periodic table and has a formal charge, what adjustment can be made?

Accepted Answer

Form a multiple bond to eliminate the excess formal charge.

Question 15

Which of the following best describes the bonding in $\mathrm{CH_4}$ (methane)?

Accepted Answer

Carbon forms four single bonds with hydrogen.

Question 16

A molecule of $\mathrm{BF_3}$ is found to be stable even though boron has only six electrons in its valence shell. What is this an example of?

Accepted Answer

An incomplete octet

Question 17

Which of the following molecules would you expect to have resonance structures?

Accepted Answer

$\mathrm{O_3}$

Question 18

In the Lewis structure for $\mathrm{H_2O}$, how many lone pairs are present on the oxygen atom?

Accepted Answer

Two lone pairs

Question 19

Which of the following is the correct Lewis dot structure for a chlorine atom?

Accepted Answer

$\mathrm{Cl}$ with 7 dots

Question 20

Which of the following molecules contains a double bond in its Lewis structure?

Accepted Answer

$\mathrm{C_2H_4}$

Lewis Structures: Fundamentals and Applications in GOB Chemistry

Study Guide - Practice Questions