Lewis Dot Structures for Covalent Bonds (9.2.1)

Question 1

Which of the following is the most stable according to the prediction of the Lewis bonding theory?

Answer 1

Cl2 (A)

Each chlorine atom in a Cl2 molecule has 8 valence atoms, consistent with the prediction of the Lewis theory that 8 are necessary for stability.

Question 2

How many valence electrons are in lone pairs in the Lewis dot structure of C2H2? The carbon atoms are bonded to each other, and each hydrogen atom is bonded to a carbon atom.

Answer 2

0 (D)

The correctly drawn Lewis dot structure of C2H2, H:C:::C:H, has 2 carbon atoms that each provide 4 electrons and 2 hydrogen atoms that each provide 1 electron, making a total of 10 electrons in 5 bonding pairs. The structure contains no lone pair valence electrons.

Question 3

Which two molecules are not isoelectronic in terms of total valence electrons?

Answer 3

FCl and HCl (A)

FCl has 14 valence electrons (7 each from fluorine and from chlorine), and HCl has 8 valence electrons (1 from hydrogen and 7 from chlorine). Therefore, FCl and HCl are not isoelectronic (have the same total number of valence electrons).

Question 4

Which of the following element is the most inert according to the prediction of the Lewis bonding theory?

Answer 4

Ar (C)

Argon atoms have 8 valence electrons, and the Lewis theory predicts that 8 are necessary for stability. Argon gas is one of the noble gases, which are known for their stability and inactivity.

Question 5

How many lone pairs of electrons are in the Lewis dot structure of HF?

Answer 5

3 (C)

The Lewis dot structure of HF contains three lone pairs of valence electrons.

Question 6

Which of the following is a homonuclear diatomic molecule?

Answer 6

Cl2 (C)

A chlorine molecule contains 2 chlorine atoms, and therefore is a homonuclear diatomic molecule, which is a molecule consisting of two of the same atoms.

Question 7

Which Lewis dot structure of the nitrate anion, [ NO3 ]1−, satisfies the octet rule? In this molecule, the nitrogen atom is bonded to each of the oxygen atoms.

Answer 7

(A)

The nitrogen atom provides valence 5 electrons, each oxygen atom provides 6 valence electrons, and the negative charge associated with the anion adds 1 valence electron, for a total of 24 valence electrons. One of the oxygen atoms contributes a lone pair of electrons to become a bonding pair so that the nitrogen atom has 8 valence electrons to satisfy the octet rule.

Question 8

Which atoms follow the duet rule in filling up their valence shells electrons?

Answer 8

He and H (B)

Helium atoms and hydrogen atoms follow the duet rule and need 2 electrons to fill their valence shells.

Question 9

Which two molecules have the same number of total valence electrons?

Answer 9

HF and CH4 (A)

HF has 8 valence electrons (1 from hydrogen and 7 from fluorine), and CH4 also has 8 valence electrons (4 from carbon and 1 from each hydrogen). Therefore, HF and CH4 have the same total number of valence electrons.

Question 10

How many electrons are in a completed valence shell of most second period atoms when they combine with other atoms to become molecules?

Answer 10

8 (D)

According to the octet rule, most atoms need 8 electrons to fill their valence shells.