Naming Covalent/ Molecular Compounds

Hydrogen compounds are handled differently and will be looked at first.

Nomenclature:1) Name the hydrogen that appears in the formula.

2) Name the second element that appears in the formula, changing its ending to –ide. (Similar to ionic compounds)

Examples:HCl hydrogen chloride

HI hydrogen iodide

Naming Covalent CompoundsNaming Covalent Compounds

Covalent Bonds use prefixes to indicate the number of atoms involved in the compounds

1= mono 6 = hexa

2 = di 7= hepta

3 = tri 8 = octa

4 = tetra 9 = nona

5 = penta 10 = deca

RULES

1- The name of the first element does not get changed, only a prefix is added if it is more than one.

Ex: Trisulfur tetrafluoride S3F4

2- The second element gets a different ending, as well as a prefix.

Ex : phosphorus trichloride PCl3(NOT: phosphorus trichlorine)

RULES continued..

3- If the first element in the compound is single you do not write mono:

ex. CO2 - carbon dioxide (NOT monocarbon dioxide)

4- If the element’s name starts with a vowel, and the prefix ends with a vowel, you can drop the last vowel on the prefix:

ex. S5O10 - pentasulfur decoxide(NOT pentasulfur decaoxide)

RULES continued..

5- Covalent compounds do not get simplified. Name the compound exactly as you see it:

Ex. H2F2 = dihydrogen difluoride

(NOT hydrogen monofluoride HF)

7

What is the name of SO3?

STEP 1 The first nonmetal is S sulfur.

STEP 2 The second nonmetal is O, named oxide.

STEP 3 The subscript 3 of O is shown as the prefix tri.

SO3 → sulfur trioxide

The subscript 1(for S) or mono is understood.

Naming Covalent Compounds

8

Name P4S3

STEP 1 The first nonmetal P is phosphorus.

STEP 2 The second nonmetal S is sulfide.

STEP 3 The subscript 4 of P is shown as tetra.

The subscript 3 of O is shown as tri.

P4S3 → tetraphosphorus trisulfide

Naming Covalent Compounds (Continued)

9

Names of Covalent Compounds

Remember Prefixes are used in the names of covalent compounds because two nonmetals can form two or more

different compounds

Examples of compounds of N and O:

NO nitrogen oxide

NO2 nitrogen dioxide

N2O dinitrogen oxide

N2O4 dinitrogen tetroxide

N2O5 dinitrogen pentoxide

10

Select the correct name for each compound.

A. SiCl4 1) silicon chloride

2) tetrasilicon chloride

3) silicon tetrachloride

B. P2O5 1) phosphorus oxide

2) phosphorus pentoxide

3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

2) dichlorine oxide

3) chlorine heptoxide

Learning Check

11

Select the correct name for each compound.

A. SiCl4 3) silicon tetrachloride

B. P2O5 3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

Solution

12

Write the correct formula for each of the following:

A. phosphorus pentachloride

B. dinitrogen trioxide

C. sulfur hexafluoride

Learning Check

13

Write the correct formula for each of the following:

A. phosphorus pentachloride

1P penta = 5Cl PCl5B. dinitrogen trioxide

di = 2N tri = 3 O N2O3

C. sulfur hexafluoride

1S hexa = 6F SF6

Solution

TRY THESE:

a) Diphosphorus pentoxide

b) Nitrogen monoxide

c) Xenon hexafluoride

d) Tetrarsenic decoxide

a) SiO2

b) N2S5

c)P4O10

d)BrCl6

More Examples

16

Formulas, Names and Uses of Some Covalent Compounds

17

Write the name of each covalent compound.

CO _____________________

CO2 _____________________

PCl3 _____________________

CCl4 _____________________

N2O _____________________

Learning Check

18

Write the name of each covalent compound.

CO carbon monoxide

CO2 carbon dioxide

PCl3 phosphorus trichloride

CCl4 carbon tetrachloride

N2O dinitrogen oxide

Solution

HI hydrogen iodide

NF3 nitrogen trifluoride

SO2 sulfur dioxide

N2Cl4 dinitrogen tetrachloride

NO2 nitrogen dioxide

N2O dinitrogen monoxide

Review of Covalent Compounds

20

Ionic and Covalent

Identify each compound as ionic or covalent, and give its correct name.

A. SO2

B. BaCl2

C. (NH4)3PO4

D. Cu2CO3

E. N2O4

21

Solution

Identify each compound as ionic or covalent, and give its correct name.

A. SO2 covalent; sulfur dioxide

B. BaCl2 ionic; barium chloride

C. (NH4)3PO4 ionic; ammonium phosphate

D. Cu2CO3 ionic; copper(I) carbonate

E. N2O4 covalent; dinitrogen tetroxide

22

Learning Check

Name the following compounds:

A. Ca3(PO4)2

B. FeBr3

C. SCl2D. Cl2O

23

Solution

Name the following compounds:

A. Ca3(PO4)2 ionic Ca2+, PO43− calcium

phosphate

B. FeBr3 ionic Fe3+, Br − iron(III) bromide

C. SCl2 covalent 1S, 2Cl sulfur dichloride

D. Cl2O covalent 2Cl, 1 O dichlorine oxide

Homework

Page 249Problems: 14, 15, 16 and 17

Page 274Problems: 93, 94 and 95 (a-c)