Q: A student is asked to draw the Lewis Dot Structure for $$\mathrm{NH_2OH}. $$Which of the following is a correct first step?

Count the total number of valence electrons: $$N=5$$, $$H=1\times4=4$$, $$O=6$$; Total $$=15$$

Question 1

Which of the following best describes the purpose of a Lewis Dot Structure?

Accepted Answer

To represent the arrangement of valence electrons and show how atoms share electrons to form covalent bonds.

Question 2

What is the total number of valence electrons in a molecule of $$\mathrm{NH_3$}$$?

Accepted Answer

$$14$$

Question 3

When drawing the Lewis Dot Structure for $$\mathrm{$$SiBr_4$$}$$, what is the correct number of valence electrons to use?

Accepted Answer

$$32$$

Question 4

Which step is necessary to ensure the octet rule is satisfied when drawing Lewis Dot Structures?

Accepted Answer

Adding lone pairs to outer atoms until they have eight electrons, then placing remaining electrons on the central atom.

Question 5

Which molecule below would require double bonds in its Lewis Dot Structure to satisfy the octet rule?

Accepted Answer

$$\mathrm{CO_2$}$$

Question 6

A student draws the Lewis Dot Structure for $$\mathrm{NH_4$^+}$$ and places a lone pair on the nitrogen atom. What is the error in this structure?

Accepted Answer

There should be no lone pairs on nitrogen because all valence electrons are used in bonding.

Question 7

Which of the following is the correct Lewis Dot Structure for $$\mathrm{H_2O}$$?

Accepted Answer

Oxygen with two single bonds to hydrogen and two lone pairs on oxygen.

Question 8

How many bonding pairs and lone pairs are present in the Lewis Dot Structure of $$\mathrm{NH_3$}$$?

Accepted Answer

3 bonding pairs, 1 lone pair

Question 9

Which of the following compounds violates the octet rule in its Lewis Dot Structure?

Accepted Answer

$$\mathrm{BF_3$}$$

Question 10

A chemist is drawing the Lewis Dot Structure for $$\mathrm{CH_2O} ($$formaldehyde). After assigning single bonds, there are not enough electrons to satisfy the octet rule for carbon. What should the chemist do next?

Accepted Answer

Form a double bond between carbon and oxygen.

Question 11

Which of the following steps is performed first when drawing a Lewis Dot Structure?

Accepted Answer

Determining the total number of valence electrons.

Question 12

In the Lewis Dot Structure for $$\mathrm{NH_4$^+}$$, what is the formal charge on the nitrogen atom?

Accepted Answer

$$0$$

Question 13

Which of the following best explains why hydrogen atoms are always placed on the outside in Lewis Dot Structures?

Accepted Answer

Hydrogen can only form one bond and cannot have more than two electrons.

Question 14

A student is asked to draw the Lewis Dot Structure for $$\mathrm{NH_2OH}. $$Which of the following is a correct first step?

Accepted Answer

Count the total number of valence electrons: $$N=5$$, $$H=1	imes4=4$$, $$O=6$$; Total $$=15$$

Question 15

Which of the following is a correct application of the octet rule in Lewis Dot Structures?

Accepted Answer

Atoms (except hydrogen and helium) tend to have eight electrons in their valence shell after bonding.

Lewis Dot Structures for Neutral Compounds: Principles and Practice

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