9.2.1 Lewis Dot Structures for Covalent Bonds

Question 1

Lewis Dot Structures for Covalent Bonds

Answer 1

• The octet rule states that, with the exception of hydrogen and helium, nonmetal atoms are most stable in molecules and ions when surrounded by eight electrons.
• Lewis dot structures offer a convenient means of accounting for electrons in molecules and illustrating covalent bonding.

Question 2

note

Answer 2

• The octet rule states that nonmetal atoms are most stable in molecules and ions when surrounded by eight electrons. There are exceptions to this rule.
• Exception 1: The elements hydrogen and helium (in the
  first period) require only two electrons to be stable because they are filling the 1s orbital, which only holds two electrons.
• When there are not enough electrons to fill an atom’s octet, lone pair electrons from an adjacent atom can be brought in to form a double bond or a triple bond between the atoms.
• How to draw Lewis dot structures:
  1. Calculate the total number of valence electrons
  in the molecule.
  2. Place them around the structure so that the
  octet rule is satisfied.
• Electron placement:
• Electrons should be placed in pairs. The general order of the placement of electrons is:
  1. Bonding pairs are first.
  2. one pairs in surrounding atoms are next.
  3. Any remaining pairs of electrons go back
  on the central atom as lone pairs.

Question 3

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 3

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 4

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

Answer 4

HF and CH4

Question 5

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

Answer 5

3

Question 6

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

Answer 6

8

Question 7

Which of the following is a homonuclear diatomic molecule?

Answer 7

Cl2

Question 8

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

Answer 8

He and H

Question 9

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

Answer 9

FCl and HCl

Question 10

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

Answer 10

Cl2

Question 11

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 11

0

Question 12

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

Answer 12

Ar