Question 1

Which of the following best describes the purpose of Lewis symbols in chemistry?

Accepted Answer

To represent the valence electrons of an atom as dots around the element symbol.

Question 2

How many valence electrons are present in a chlorine atom, as shown by its Lewis symbol?

Accepted Answer

$$7$$

Question 3

Which of the following is the correct Lewis structure for methane ($$CH_4$$)?

Accepted Answer

A central carbon atom with four single bonds to four hydrogen atoms, no lone pairs on carbon.

Question 4

What is the formula for calculating the formal charge (FC) on an atom in a Lewis structure?

Accepted Answer

$$FC = VE - BE + BON$$

Question 5

Which of the following molecules violates the octet rule?

Accepted Answer

$$BF_3$$

Question 6

How many resonance structures can be drawn for the carbonate ion ($$CO_3$$^{2-}$$)?

Accepted Answer

$$3$$

Question 7

Which of the following ions has more than an octet of electrons around the central atom?

Accepted Answer

$$SO_4$$^{2-}$$

Question 8

In the Lewis structure for $$C_2H_4 ($$ethylene), what type of bond exists between the two carbon atoms?

Accepted Answer

A double bond

Question 9

Which of the following is a correct step in drawing a Lewis structure for a polyatomic ion?

Accepted Answer

Add electrons for each negative charge.

Question 10

Given the Lewis structure for $$Cl_2CO$$, how many valence electrons are present in the molecule?

Accepted Answer

$$32$$

Question 11

Which of the following best explains why $$NO$$ does not obey the octet rule?

Accepted Answer

Nitrogen has fewer than eight electrons.

Question 12

Which of the following is a valid resonance structure for $$SO_2$$?

Accepted Answer

One S=O bond is a double bond and the other is a single bond, with lone pairs adjusted accordingly.

Question 13

What is the formal charge on the central atom in $$NO_3$$^-$$ when all single bonds are used?

Accepted Answer

$$+2$$

Question 14

Which of the following molecules or ions has a central atom that does NOT obey the octet rule due to having fewer than eight electrons?

Accepted Answer

$$BF_3$$

Question 15

How many lone pairs are present on the central atom in the Lewis structure of $$NH_3$$?

Accepted Answer

$$1$$

Question 16

Which of the following is the best Lewis structure for the $$NO_2$$^-$$ ion?

Accepted Answer

A central N atom with one single bond and one double bond to O atoms, and one lone pair on N.

Question 17

Which of the following statements about resonance structures is correct?

Accepted Answer

Resonance structures differ only in the arrangement of electrons.

Question 18

Which of the following molecules has a central atom with an expanded octet?

Accepted Answer

$$SO_4$$^{2-}$$

Question 19

What is the total number of valence electrons in the $$PO_4$$^{3-}$$ ion?

Accepted Answer

$$32$$

Question 20

Which of the following is the correct Lewis structure for $$C_2H_2 ($$acetylene)?

Accepted Answer

A triple bond between the two carbon atoms, each carbon bonded to one hydrogen atom.

Lewis Structures, Formal Charges, and Resonance in General Chemistry

Study Guide - Practice Questions