Chapter 4 : Covalent Bonding and Simple Molecular Compounds

Define covalent bond.

A covalent bond is formed when two atoms share electrons.

What is

electron

sharing?

Electron

sharing joins two atoms in a covalent bond. This is a more stable arrangement than 2 individual atoms.

Draw the Lewis diagram for the covalent bond in the H2

molecule

.

H:H, H-H

Draw the Lewis diagram for the covalent bond in the Br2

molecule

.

Draw the Lewis diagram for the covalent bond in the HCl

molecule

.

What is the difference between a

molecule

and a formula unit?

molecule

is a discrete combination of atoms; a

formula unit

is the lowest ratio of ions in a crystal.

Why do hydrogen atoms not follow the

octet rule

when they form covalent bonds?

7. Hydrogen atoms follow the duet rule (not the

octet rule

). This is because it has only one shell and this shell can only hold 2 electrons.

Draw the Lewis diagram for the covalent bonding in H2S. How many bonding electrons and nonbonding electrons are in the

molecule

?

bonding electrons: 4; nonbonding electrons: 4

Draw the Lewis diagram for the covalent bonding in CF4. How many bonding electrons and nonbonding electrons are in the

molecule

?

bonding electrons: 8; nonbonding electrons: 24

Draw the Lewis diagram for the covalent bonding in PCl3. How many bonding electrons and nonbonding electrons are in the

molecule

?

bonding electrons: 6; nonbonding electrons: 20

How many covalent bonds does a hydrogen atom typically form? Why?

Hydrogen atoms form only one covalent bond because they have only one valence

electron

to pair

How many covalent bonds does an oxygen atom typically form? Why?

Oxygen atoms form 2 covalent bonds because oxygen atoms have 6 valence electrons (2 lone pairs plus 2 unpaired electrons that are shared to achieve octet).

13. two; H2Te

Tellurium atoms make covalent bonds. How many covalent bonds would a tellurium atom make? Predict the formula of a

compound

between tellurium and hydrogen.

two; H2Te

Tin atoms make covalent bonds. How many covalent bonds would a tin atom make? Predict the formula of a

compound

between tin and hydrogen.

four: SnH4

Astatine is a synthetic element, made one atom at a time in huge "atom-smasher" machines. It is in the halogen group on the

periodic table

. How many covalent bonds would an atom of this element form?

one

There have been reports that atoms of element 116 (Lv) were made by smashing smaller atoms together. Using the

periodic table

, determine what column element 116 would be in and suggest how many covalent bonds an atom of this element would form.

two

How do you recognize a covalent compound?

A covalent compound is usually composed of two or more nonmetal elements.

What are the rules for writing the molecular formula of a simple covalent compound?

It is just like an ionic compound except that the element further down and to the left on the periodic table is listed first and is named with the element name.

What are the rules for naming a simple covalent compound?

Name the first element first and then the second element by using the stem of the element name plus the suffix -ide. Use numerical prefixes if there is more than one atom of the first element; always use numerical prefixes for the number of atoms of the second element.

Identify whether each

compound

has covalent bonds.

NaI

Na2CO3

N2O

SiO2

no

yes

yes

yes

Identify whether each

compound

has covalent bonds.

C2H6

C6H5Cl

KC2H3O2

Ca(OH)2

yes

yes

yes

yes

Identify whether each

compound

has ionic bonds, covalent bonds, or both.

Na3PO4

K2O

COCl2

CoCl2

both

ionic

covalent

ionic

Identify whether each

compound

has ionic bonds, covalent bonds, or both.

FeCl3

Fe(NO3)3

(NH2)2CO

SO3

ionic

both

covalent

covalent

Which is the correct molecular formula—H4Si or SiH4? Explain.

SiH4; except for water, hydrogen is almost never listed first in a covalent

compound

.

Which is the correct molecular formula—SF6 or F6S? Explain.

SF6; the less electronegative atom (S) is written first

Write the name for each covalent

compound

.

SiF4

NO2

CS2

P2O5

silicon tetrafluoride

nitrogen dioxide

carbon disulfide

diphosphorus pentoxide

Write the name for each covalent

compound

.

CO

S2O3

BF3

GeS2

carbon monoxide

disulfur trioxide

boron trifluoride

germanium disulfide

Write the formula for each covalent

compound

.

iodine trichloride

disulfur dibromide

arsenic trioxide

xenon hexafluoride

ICl3

S2Br2

AsO3

XeF6

Write the formula for each covalent

compound

.

boron trichloride

carbon dioxide

tetraphosphorus decoxide

germanium dichloride

BCl3

CO2

P4O10

GeCl2

Write two covalent compounds that have common rather than systematic names.

H2O and NH3 (water and ammonia) (answers will vary)

What is the name of the simplest

organic compound

? What would its name be if it followed the nomenclature for binary covalent compounds?

CH4; carbon tetrahydride

What is one clue that a

molecule

has a multiple bond?

If single bonds between all atoms do not give all atoms (except hydrogen) an octet, multiple covalent bonds may be present.

Draw the Lewis diagram for each of the following.

a. H2O

b. NH3

c. C2H6

d. CCl4

Each

molecule

contains double bonds. Draw the Lewis diagram for each. The first element is the central atom.

CS2

C2F4

COCl2

Each

molecule

contains multiple bonds. Draw the Lewis diagram for each. Assume that the first element is the central atom, unless otherwise noted.

N2

CO

HCN (The carbon atom is the central atom.)

POCl (The phosphorus atom is the central atom.)

Explain why hydrogen atoms do not form double bonds.

Hydrogen can accept only one more

electron

; multiple bonds require more than one

electron

pair to be shared.

Why is it incorrect to draw a

double bond

in the Lewis diagram for MgO?

MgO is an ionic

compound

(Mg transfers two electrons to O). The electrons are not shared hence it's incorrect to draw a

double bond

What is the name for the distance between two atoms in a covalent bond?

bond length

What does the

electronegativity

of an atom indicate?

Electronegativity

is a qualitative measure of how much an atom attracts electrons in a covalent bond.

What type of bond is formed between two atoms if the difference in electronegativities is small? Medium? Large?

nonpolar;

polar

; ionic

Which is longer—a C-H bond or a C-O bond? (Refer to Table 4.E.14.�.1.)

A C-O bond is longer.

Which is shorter—an N-H bond or a C-H bond? (Refer to Table 4.E.14.�.1.)

An H-N bond is shorter than an H-C bond.

A nanometer is 10−9 m. Using the data in Table 4.E.14.�.1 and Table 4.E.24.�.2, determine the length of each bond in nanometers.

a C-O bond

a C=O bond

an H-N bond

a C≡N bond

0.143 nm

0.120 nm

0.100 nm

0.116 nm

An angstrom (Å) is defined as 10−10 m. Using Table 4.E.14.�.1 and Table 4.E.24.�.2, determine the length of each bond in angstroms.

a C-C bond

a C=C bond

an N≡N bond

an H-O bond

1.54 Å

1.34 Å

1.10 Å

0.97 Å

Refer to Exercise 3. Why is the nanometer

unit

useful as a unit for expressing bond lengths?

Actual bond lengths are very small, so the nanometer

unit

makes the expression of length easier to understand.

Refer to Exercise 4. Why is the angstrom

unit

useful as a unit for expressing bond lengths?

Actual bond lengths are very small, so the angstrom

unit

makes the expression of length easier to understand.

Using Figure 4.E.34.�.3, determine which atom in each pair has the higher

electronegativity

.

H or C

O or Br

Na or Rb

I or Cl

C

O

Na

Cl

Using Figure 4.E.34.�.3, determine which atom in each pair has the lower

electronegativity

.

Mg or O

S or F

Al or Ga

O or I

Mg

S

Al

I

Will the electrons be shared equally or unequally across each covalent bond? If unequally, to which atom are the electrons more strongly drawn?

a C-O bond

an F-F bond

an S-N bond

an I-Cl bond

unequally toward the O

equally

unequally toward the N

unequally toward the Cl

Will the electrons be shared equally or unequally across each covalent bond? If unequally, to which atom are the electrons more strongly drawn?

a C-C bond

a S-Cl bond

an O-H bond

an H-H bond

equally

unequally toward the Cl

unequally toward the O

equally

Arrange the following bonds from least

polar

to most

polar

: H-F, H-N, H-O, H-C

The

electronegativity

difference increases from 0.4; 0.9; 1.4; 1.9. Hence, the least to most

polar

: H-C, H-N, H-O, H-F

Arrange the following bonds from least

polar

to most

polar

: C-F, C-N, C-O, C-C

The

electronegativity

difference increases from 0; 0.5; 1.0; 1.5. Hence, the least to most

polar

: C-C, C-N, C-O, C-F

How do you determine the molecular mass of a covalent compound?

The

molecular mass

is the sum of the masses of the atoms in the formula.

How do you determine the shape of a molecule?

2. The shape of a

molecule

is determined by the position of the atoms, which in turn is determined by the repulsion of the bonded and lone

electron

pairs around the central atom.

How do you determine whether a molecule is polar or nonpolar?

3. If all the bonds in a

molecule

are nonpolar, the molecule is nonpolar. If it contains identical polar bonds that are oriented symmetrically opposite each other (linear, trigonal planar or tetrahedral) then the molecule is nonpolar. If it contains polar bonds that don't cancel each other's effects, the molecule is polar.

What is the

molecular mass

of each compound?

H2S

N2O4

ICl3

HCl

34.08 amu

92.02 amu

233.25 amu

36.46 amu

What is the

molecular mass

of each compound?

O2F2

CCl4

C6H6

SO3

70.00 amu

153.81 amu

78.12 amu

80.06 amu

Aspirin (C9H8O4) is a covalent

compound

. What is its molecular mass?

180.17 amu

Cholesterol

(C27H46O) is a biologically important compound. What is its molecular mass?

386.73 amu

What is the shape of each

molecule

? State whether it is polar or nonpolar.

H2S

COCl2

SO2

bent; polar

trigonal planar; nonpolar

bent; polar

What is the shape of each

molecule

? State whether it is polar or nonpolar.

NBr3

SF2

SiH4

pyramidal; polar

bent; polar

tetrahedral; nonpolar

Predict the shape of nitrous oxide (N2O), which is used as an anesthetic. A nitrogen atom is in the center of this three-atom

molecule

. Is this polar?

linear;

polar

Predict the shape of acetylene (C2H2), which has the two carbon atoms in the middle of the

molecule

with a triple bond. What generalization can you make about the shapes of molecules that have more than one central atom?

linear; in a

molecule

with more than one central atom, the geometry around each central atom needs to be examined.

What is organic chemistry?

Organic chemistry

is the study of the chemistry of carbon compounds.

What is a functional group? Give at least two examples of functional groups.

A functional group is a specific structural arrangement of atoms or bonds that imparts a characteristic chemical reactivity to the molecule; alcohol group and carboxylic group (answers will vary).

Give three reasons why carbon is the central element in

organic chemistry

.

Carbon atoms bond reasonably strongly with other carbon atoms. Carbon atoms bond reasonably strongly with atoms of other elements. Carbon atoms make a large number of covalent bonds (four).

Are organic compounds based more on

ionic bonding

or covalent bonding? Explain.

2. Organic compounds are based on covalent bonding or

electron

sharing. The atoms C, H, O, N that make up organic compounds are all nonmetals.

Identify the type of hydrocarbon in each structure.

a. alkane

b. alkene

c. alkene

d. alkyne

Identify the type of hydrocarbon in each structure.

a. alkene

b. alkane

c. alkyne

d. alkene

Identify the

functional group

(s) in each

molecule

.

a. alcohol

b. carboxyl

c. alcohol

d. alkene and alkyne

Identify the

functional group

(s) in each

molecule

.

a carbon-carbon double bond and alcohol

carboxyl group

carbon-carbon double bond and alcohol

carbon-carbon double bond; alcohol and carboxyl group

How many

functional groups

described in this section contain carbon and hydrogen atoms only? Name them.

7. two; carbon-carbon double bonds and carbon-carbon

triple bonds

What is the difference in the ways the two oxygen atoms in the

carboxyl group

are bonded to the carbon atom?

8. There are two oxygen atoms in a

carboxyl group

: one is double-bonded while the other is OH, single bonded to the same carbon atom.

1. An atomic mass unit equals 1.661 × 10−24 g. What is the mass in grams of each molecule of

(a) H2S

(b) N2O4

(c) ICl3

(d) NCl3?

a: 5.661 × 10^−23 g

b: 1.528 × 10^−22 g

c: 3.874 × 10^−22 g

d: 1.999 × 10^−22 g

2. An atomic mass unit equals 1.661 × 10−24 g. What is the mass in grams of

(a) O2F2

(b) CCl4

(c) C6H6

(d) SO3?

a: 1.163 × 10^−22 g

b: 2.555 × 10^−22 g

c: 1.298 × 10^−22 g

d: 1.330 × 10−22 g

3. An atomic mass unit equals 1.661 × 10−24 g. What is the mass in grams of 5.00 × 1022 molecules of C9H8O4?

14.96 g

4. An atomic mass unit equals 1.661 × 10−24 g. What is the mass in grams of 1.885 × 1020 molecules of C27H46O?

0.1211 g

5. Acetic acid has the following structure:

This molecule can lose a hydrogen ion (H+) and the resulting anion can combine with other cations, such as Na+:

Name this ionic

compound

sodium acetate

6. Formic acid (HCOOH) loses a hydrogen ion to make the formate ion (HCOO−). Write the formula for each ionic compound: potassium formate, calcium formate, and ferric formate.

a. KHCOO

b. Ca(HCOO)2

c. Fe(HCOO)3

7. Cyanogen has the formula C2N2. Propose a bonding scheme that gives each atom the correct number of covalent bonds. (Hint: the two carbon atoms are in the center of a linear molecule.)

:N≡C-C≡N:

8. How many carbon-carbon single bonds, linked together, are needed to make a carbon chain that is 1.000 cm long?

6.49 × 107 C-C bonds

9. How many carbon-carbon double bonds, linked together, are needed to make a carbon chain that is 1.000 cm long?

7.46 × 107 C=C bonds

10. In addition to themselves, what other atoms can carbon atoms bond with and make covalent bonds that are nonpolar (or as nonpolar as possible)?

Hydrogen atoms make relatively nonpolar bonds with carbon atoms.

11. What is the greatest possible electronegativity difference between any two atoms? Use Figure 4.4 to find the answer.

The greatest electronegativity difference is 3.2, between F and Rb.

12. Acetaminophen, a popular painkiller, has the following structure:

Name the recognizable

functional groups

in this molecule. Do you think there are other groups of atoms in this molecule that might qualify as functional groups?

alcohol

; the ring with double bonds, and the O=C-NH are also likely functional groups.

Glutamic acid is the parent compound of monosodium glutamate (known as MSG), which is used as a flavor enhancer. Glutamic acid has the following structure:

Name the

functional groups

you recognize in this molecule. Do you think there are other groups of atoms in this molecule that might qualify as functional groups?

carboxyl and -NH2 functional groups