1 Chapter 5 Molecules and Covalent Compounds 5.5 Covalent Compounds and Their Names Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin.

1

Chapter 5 Molecules and Covalent Compounds

5.5

Covalent Compounds and Their Names

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

2

Forming a H2 Molecule

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

3

H2, A Covalent Molecule

In a hydrogen (H2) molecule

• Two hydrogen atoms share electrons to form a covalent single bond.

• Each H atom acquires two (2) electrons.

• Each H becomes stable like helium (He).

Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

4

Diatomic Elements

• These elements share electrons to form diatomic, covalent molecules.Table 5.9

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

5

What is the name of each of the following diatomic molecules?

H2 ______________________

N2 _______________

Cl2 _______________

O2 _______________

I2 _______________

Learning Check

6

What are the names of each of the following diatomic molecules?

H2 hydrogen

N2 nitrogen

Cl2 chlorine

O2 oxygen

I2 iodine

Solution

7

Electron-Dot Formulas

Electron-dot formulas show

• The order of bonded atoms in a covalent compound.

• The bonding pairs of electrons between atoms.

• The unshared (lone) valence electrons.

• A central atom with an octet.

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8

Electron-Dot Formulas and Models of Some Covalent Compounds

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

Table 5.10

9

Names of Covalent Compounds

Prefixes are used• In the names of covalent compounds.• Because two nonmetals can form two or more different

compounds.

• If the element begins with a vowel then the vowel on the prefix is omitted.• E.g., Carbon mono-oxide becomes

Carbon monoxide

Exception – the vowel “i” is kept

E.g., Boron tri-iodide becomes

Boron triiodide

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Naming Covalent Compounds

STEP 1 Name the first nonmetal as the element.

STEP 2 End the name of the

second nonmetal

with -ide

STEP 3 Use prefixes to show the number of

atoms (subscripts).

* Mono is usually omitted for the first element but used for the second.

Table 5.11

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Examples

Examples of compounds of N and O:

NO nitrogen monoxide

NO2 nitrogen dioxide

N2O dinitrogen oxide

N2O4 dinitrogen tetroxide

N2O5dinitrogen pentoxide

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12

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

Remember not to use mono for the first

element!!

Naming Covalent Compounds

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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

14

Formulas and Names of Some Covalent Compounds

Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

TABLE 4.13

15

Select the correct name for each compound.

A. SiCl4 1) silicon chloride

2) tetrasilicon chloride3) silicon tetrachloride

B. P2O5 1) phosphorus oxide

2) phosphorus pentoxide3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

2) dichlorine oxide3) chlorine heptoxide

Learning Check

16

Select the correct name for each compound.

A. SiCl4 3) silicon tetrachloride

B. P2O5 3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

Solution

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

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STEP 1 Write the symbols in the order of the

elements in the name.

STEP 2 Write any prefixes as subscripts.

Example: Write the formula for carbon disulfide.

STEP 1 Elements are C and S

STEP 2 No prefix for carbon means 1 C

Prefix di = 2

Formula: CS2

Guide to Writing Formulas

20

Write the correct formula for each of the following:

A. phosphorus pentachloride

B. dinitrogen trioxide

C. sulfur hexafluoride

Learning Check

21

Write the correct formula for each of the following:

A. phosphorus pentachloride

1 P penta = 5 Cl PCl5

B. dinitrogen trioxide

di = 2 N tri = 3 O N2O3

C. sulfur hexafluoride

1 S hexa = 6 F SF6

Solution

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Learning Check

Identify each compound as ionic or covalent and

give its correct name.

A. SO3

B. MnCl2

C. (NH4)3PO4

D. Cu2CO3

E. N2O4

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SolutionIdentify each compound as ionic or covalent and

give its correct name.

A. SO3 covalent - sulfur trioxide

B. MnCl2 ionic - manganese(II) chloride

C. (NH4)3PO3 ionic - ammonium phosphite

D. Cu2CO3 ionic – copper(I) carbonate

E. N2O4 covalent – dinitrogen tetroxide

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Learning Check

Identify each compound as ionic or covalent and

give its correct name.

A. Ca3(PO4)2

B. FeBr3

C. SCl2

D. Cl2O

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Solution

A. Ca3(PO4)2

ionic Ca2+ PO43− calcium phosphate

B. FeBr3

ionic Fe3+ Br − iron(III) bromide

C. SCl2

covalent 1S 2 Cl sulfur dichloride

D. Cl2O

covalent 2 Cl 1 O dichlorine oxide