Question 1

Which of the following statements best describes a Lewis structure?

Accepted Answer

A representation of the bonding between atoms in a molecule using valence electrons.

Question 2

When drawing the Lewis structure for $$\mathrm{CO_3$^{2-}}$$, how many total valence electrons should you use?

Accepted Answer

$$24$$

Question 3

Which atom should generally be chosen as the central atom when drawing a Lewis structure?

Accepted Answer

The least electronegative atom (excluding hydrogen and halogens if possible).

Question 4

What is the formal charge on the central carbon atom in $$\mathrm{CO_2$}$$?

Accepted Answer

$$0$$

Question 5

Which of the following formulas correctly calculates the formal charge (FC) on an atom?

Accepted Answer

$$\mathrm{FC = \#\ valence\ electrons - (total\ electrons\ in\ lone\ pairs + \frac{1}{2}(total\ electrons\ in\ bonds))}$$

Question 6

Which of the following molecules or ions is most likely to have an incomplete octet in its Lewis structure?

Accepted Answer

$$\mathrm{BF_3$}$$

Question 7

Which of the following elements can have an expanded octet in its Lewis structure?

Accepted Answer

Sulfur

Question 8

In the resonance structures of $$\mathrm{CO_3$^{2-}}$$, what is the formal charge on each oxygen atom in the most stable structure?

Accepted Answer

Two oxygens have $$0$$, one has $$-1$$

Question 9

Which of the following is NOT a correct guideline for drawing Lewis structures?

Accepted Answer

Hydrogen should be placed in the center of the molecule.

Question 10

A molecule has two or more valid Lewis structures that differ only in the placement of electrons. What is this phenomenon called?

Accepted Answer

Resonance

Question 11

Which of the following best describes the 'actual' structure of a molecule with resonance?

Accepted Answer

A weighted average of all possible resonance structures.

Question 12

Which of the following is true about formal charges in the most stable resonance structure?

Accepted Answer

The sum of all formal charges equals the overall charge of the molecule or ion.

Question 13

Which of the following molecules is most likely to have an expanded octet?

Accepted Answer

$$\mathrm{SF_6$}$$

Question 14

Which of the following is a correct step when drawing the Lewis structure for $$\mathrm{HCN}$$?

Accepted Answer

Connect H and N to C using single bonds, then use double or triple bonds if needed to fill valence shells.

Question 15

Which of the following ions requires the use of brackets in its Lewis structure?

Accepted Answer

$$\mathrm{NO_3$^-}$$

Question 16

In a Lewis structure, which atom should receive a negative formal charge if it cannot be avoided?

Accepted Answer

The most electronegative atom.

Question 17

Which of the following is a real-world application of Lewis structures?

Accepted Answer

Predicting the reactivity of a drug molecule based on its electron distribution.

Question 18

Which of the following molecules is an example of an incomplete octet?

Accepted Answer

$$\mathrm{$$BeCl_2$$}$$

Question 19

Which of the following is NOT a possible reason for multiple valid Lewis structures for a molecule?

Accepted Answer

Different arrangement of atoms (skeletal structure).

Question 20

Which of the following best explains why halogens are generally not chosen as central atoms in Lewis structures?

Accepted Answer

Halogens are highly electronegative and prefer to form only one bond.

Lewis Structures and Formal Charge: Lecture 12

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