Question 1

Which of the following best describes a covalent bond in a Lewis structure?

Accepted Answer

A pair of electrons shared between two atoms, represented by a line.

Question 2

How many total valence electrons are present in a molecule of $\mathrm{H_2O}$?

Accepted Answer

$8$

Question 3

When drawing the Lewis structure for $\mathrm{CO_2}$, what is the correct total number of valence electrons to use?

Accepted Answer

$16$

Question 4

Which atom is typically chosen as the central atom when drawing the Lewis structure for $\mathrm{H_2O}$?

Accepted Answer

Oxygen

Question 5

In the Lewis structure for $\mathrm{NH_3}$, how many lone pairs are present on the nitrogen atom?

Accepted Answer

$1$

Question 6

What is the correct Lewis structure for $\mathrm{F_2}$?

Accepted Answer

$\mathrm{:F-F:}$, each F has three lone pairs

Question 7

Which of the following is the correct sequence of steps for drawing a Lewis structure for a covalent compound?

Accepted Answer

Count valence electrons, draw skeletal structure, complete octets, check if used equals total.

Question 8

For the polyatomic ion $\mathrm{NO_3^-}$, how many total valence electrons should be used when drawing its Lewis structure?

Accepted Answer

$24$

Question 9

Which statement about resonance structures is correct?

Accepted Answer

Resonance structures are multiple valid electron-dot structures for the same molecule.

Question 10

In the Lewis structure for $\mathrm{CO_2}$, what type of bonds are present between the carbon and oxygen atoms?

Accepted Answer

Two double bonds

Question 11

Which of the following molecules violates the octet rule in its Lewis structure?

Accepted Answer

$\mathrm{BF_3}$

Question 12

When drawing the Lewis structure for $\mathrm{O_2^{2-}}$ (peroxide ion), how many total valence electrons should be used?

Accepted Answer

$18$

Question 13

Which of the following best explains why hydrogen only needs two electrons in its Lewis structure?

Accepted Answer

Hydrogen achieves a stable configuration with two electrons, filling its $1s$ orbital.

Question 14

A student draws the Lewis structure for $\mathrm{PCl_3}$ and places three lone pairs on phosphorus. What is the error in this structure?

Accepted Answer

Phosphorus should have only one lone pair; the other electrons are used in bonds with chlorine.

Question 15

Which of the following is a correct Lewis structure for $\mathrm{CO}$ (carbon monoxide)?

Accepted Answer

$\mathrm{:C\equiv O:}$, with one lone pair on C and two on O

Question 16

In the Lewis structure for $\mathrm{SO_2}$, which of the following is true regarding resonance?

Accepted Answer

There are two major resonance structures, each with a double bond to a different oxygen.

Question 17

A hospital uses $\mathrm{O_2}$ gas for patient care. What is the correct Lewis structure for $\mathrm{O_2}$?

Accepted Answer

$\mathrm{:O=O:}$, each O has two lone pairs

Question 18

Which of the following steps is necessary when drawing the Lewis structure for a polyatomic ion with a negative charge?

Accepted Answer

Add one electron for each negative charge to the total valence electron count.

Question 19

A student is drawing the Lewis structure for $\mathrm{CO_2}$ and finds that the number of electrons used exceeds the total available. What should the student do next?

Accepted Answer

Remove a lone pair and add a multiple bond between atoms.

Covalent Bonding and Electron-Dot (Lewis) Structures

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