Chapter 9 Practice Test

Question 1

How many valence electrons are found in an atom of nitrogen?

Answer 1

5

Question 2

Which of the following is the correct Lewis dot structure for carbon dioxide?

Answer 2

A carbon atom has 4 valence electrons and an oxygen atom has 6 valence electrons. Therefore, a compound composed of one carbon atom and two oxygen atoms should have a total of 16 valence electrons(4 from C and 2 × 6 = 12 from O). In a Lewis Dot structure, those atoms need to be placed in such a way that each atom of a covalent compound has 8 valence electrons surrounding it.

Question 3

The electron configuration for sulfur is 1s 22s 22p 63s 23p 4. How many valence electrons does a sulfur atom have?

Answer 3

6

Question 4

Which of the following formulas accurately represents the binary ionic compound formed between magnesium and chlorine?

Answer 4

MgCl2

Question 5

Which one of the following binary ionic compounds is expected to have the highest melting point?

Answer 5

MgS

Question 6

Which one of the following binary ionic compounds is expected to have the lowest lattice energy?

Answer 6

NaCl

Question 7

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

Answer 7

He and H

Question 8

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 8

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 9

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

Answer 9

HF and CH4

Question 10

The beryllium (Be) atom has 2 valence electrons, and when beryllium is the central atom of a molecule such as beryllium dichloride, BeCl2, it has only 4 valence electrons instead of 8 according to the octet rule. Which of the following is the correctly drawn Lewis dot structure of BeCl2?

Answer 10

The beryllium atom provides 2 valence electrons, and each chlorine atom provides 7 valence electrons, for a total of 16 valence electrons. The beryllium atom has a single bond to each chlorine atom

Question 11

Which of the following is the correctly drawn Lewis dot structure of sulfuric acid, H2SO4? In this molecule, the sulfur atom has an expanded octet of 12 valence shell electrons.

Answer 11

The sulfur atom provides 6 valence electrons, each oxygen atom provides 6 valence electrons, and each hydrogen atom provides 1 electron, for a total of 32 valence electrons. In this Lewis Dot structure, the sulfur atom has an expanded octet of 12 valence electrons.

Question 12

Which of the following molecules has an odd number of valence electrons?

Answer 12

NO2

Question 13

Which of the following is not a reasonable resonance structure for the [ NCO]− anion in which the carbon atom is the central atom?

Answer 13

This is not a reasonable resonance structure for an [ NCO]− anion in which the carbon atom is the central atom. The order of the atoms was changed so that the oxygen atom is the central atom.

Question 14

Which structure of sulfuric acid, H2SO4, is not equivalent to the other three?

Answer 14

This structure has only 8 octet electrons drawn for the sulfur atom, whereas the other structures have 12. This structure also has only single bonds between the sulfur atom and the oxygen atoms, whereas the other structures have double bonds between the sulfur atom and 2 of the oxygen atoms.

Question 15

For which of the following molecules is it possible to draw resonance structures?

Answer 15

NO3−

Question 16

What are the formal charges on the atoms in sulfur dioxide, shown below?

Answer 16

left oxygen: −1; sulfur: +1; right oxygen: 0

Question 17

What is a resonance structure?

Answer 17

A resonance structure is a hybrid of two or more Lewis dot structures that both contribute to the description of the bonding in a molecule.

Question 18

What is the formal charge of S in the Lewis dot structure shown above?

Answer 18

0

Question 19

Which of the following statements is not correct?

Answer 19

An atom with a low electronegativity and a formal charge of 0 will have a tendency to acquire another electron.

Question 20

What is electronegativity?

Answer 20

Electronegativity is a quantitative measure of the tendency of an atom to attract electrons to itself

Question 21

Which of the following is not a principal characteristic of atoms and molecules that scientists use to predict chemical behavior?

Answer 21

chemical use of a substance

Question 22

Carbon tetrachloride, CCl4, contains four C–Cl bonds. The reaction belowshows that a certain amount of energy is needed to break one of the C–Cl bonds. The products are CCl3 + Cl.

Successive addition of the same amount of energy will break one C–Cl bond at a time

CCl3 + energy → CCl2 + Cl
CCl2 + energy → CCl + Cl
CCl + energy → C + Cl

For each step, the energy needed to break one C–Cl bond is almost the same. This energy is called the bond energy.

Which of the following statements is not true about bond energy?

Answer 22

The average bond energy of a carbon-chlorine molecule is the energy you have to remove in order to break 1 mol of C–Cl bond.

Question 23

An electronegativity difference of 2.2 is observed between two species in a molecule. What type of bond will these interactions produce?

Answer 23

An ionic bond

Question 24

Calculate the ΔH, of the reaction below and identify whether the reaction is endothermic or exothermic.

N2(g) + 2O2(g) → 2NO2(g)

ΔH°f (NO2 ) = 33.2 kJ / mol NO2
ΔH°f O2 = ΔH°f N2 = 0

Answer 24

66.4 kJ; endothermic

Question 25

What is enthalpy?

Answer 25

Enthalpy is a numerical description of the amount of heat energy a substance has at a given temperature and pressure.