Chapter 4 Compounds and Their Bonds

4.1 Octet Rule and Ions 1

Octet Rule • • An

octet

is

8 valence electrons

.

is associated with the stability of the noble gases.

He is stable with 2 valence electrons (duet).

He

2

Ne 2,

8

Ar 2, 8,

8

Kr 2, 8, 14,

8 valence electrons 2 8 8 8 2

Ionic and Covalent Bonds Atoms that are not noble gases form

octets

• to become more stable. • by

losing, gaining, or sharing

valence electrons.

• by forming ionic bonds or covalent bonds.

3

Metals Form Positive Ions • • •

Metals

form positive ions by a loss of their valence electrons.

with the electron configuration of the nearest noble gas.

that have fewer electrons than protons. Group 1A metals Group 2A metals Group 3A metals ion 1+ ion 2+ ion 3+

4

Formation of a Sodium Ion, Na +

5

Charge of Sodium Ion, Na + With the loss of its valence electron, the sodium ion has a 1+ charge.

Na atom

11p + 11e -

Na

11p 10e 0 1 + -

+

+

ion

2, 8 Copyright © 2009 by Pearson Education, Inc.

6

Formation of Mg 2+ Magnesium achieves an octet by losing its two valence electrons.

7

Charge of Magnesium Ion, Mg 2+ With the loss of two valence electrons, magnesium forms a positive ion with a 2+ charge.

Mg atom

12p + 12e-

Mg 2+ ion

12p + 10e 0 2+

8

Examples A. The number of valence electrons in aluminum is 1) 1e .

2) 2e .

3) 3e .

B. The change in electrons for octet requires a 1) loss of 3e .

2) gain of 3e .

3) a gain of 5e .

C.

1) 3-.

The ionic charge of aluminum is 2) 5-.

D. The symbol for the aluminum ion is 1) Al 3+ .

2) Al 3 .

3) 3+. 3) Al + .

9

Formation of Negative Ions In ionic compounds,

nonmetals

in Groups 5A (15), 6A (16) and 7A (17) • • achieve an octet arrangement by gaining electrons.

form negatively charged ions with 3-, 2-, or 1 charges.

10

Formation of a Chloride, Cl Chlorine achieves an octet by adding an electron to its valence electrons.

11

Charge of a Chloride Ion, Cl By gaining 1 electron, the chloride ion has a 1- charge.

Chlorine atom, Cl Chloride ion, Cl

– 17p + 17p + 17e 0 18e 1 – Copyright © 2009 by Pearson Education, Inc.

12

Ionic Charge from Group Numbers • The charge of a positive ion is equal to its Group number.

Group

1A(1)

=

1+

Group

2A(2)

=

2+

Group

3A(3)

=

3+

• The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group

6A(16)

=

6

- 8 =

2-

or

16

- 18 =

2 13

Some Ionic Charges

14

Examples A. The number of valence electrons in phosphorous is 1) 4e .

2) 5e .

3) 8e .

B. The change in electrons for octet requires a 1) loss of 2e .

2) gain of 2e . 3) a gain of 3e .

C.

1) 2+.

The ionic charge of sulfur is 2) 3-.

3) 4-.

15

Chapter 4 Compounds and Their Bonds

4.2

Ionic Compounds

16

Ionic Compounds

Ionic compounds

• consist of positive and negative ions.

• have attractions called

ionic bonds

between positively and negatively charged ions. • have high melting and boiling points.

• are solid at room temperature.

17

Salt Is An Ionic Compound Sodium chloride or “table salt” is an example of an ionic compound .

18

Ionic Formulas An

ionic formula

• consists of positively and negatively charged ions.

• is neutral.

• has charge balance.

total positive charge = total negative charge

The symbol of the metal is written first, followed by the symbol of the nonmetal.

19

Charge Balance for NaCl, “Salt” In NaCl, • • • a Na atom loses its valence electron. a Cl atom gains an electron.

the symbol of the metal is written first, followed by the symbol of the nonmetal.

20

Charge Balance in MgCl2 In MgCl 2 , • a Mg atom loses 2 valence electrons.

• two Cl atoms each gain 1 electron.

• subscripts indicate the number of ions needed to give charge balance.

21

Charge Balance in Na 2 S • • In Na 2 S, two Na atoms lose 1 valence electron each. one S atom gains 2 electrons.

• subscripts show the number of ions needed to give charge balance.

22

Writing Ionic Formulas from Charges Charge balance is used to write the formula for sodium nitride, a compound containing Na + and N 3− .

3 Na + Na + + N 3− Na + = Na 3 N 3(+1) + 1(3-) = 0 23

Formula from Ionic Charges Write the ionic formula of the compound with Ba 2+ and Cl  .

• • • Write the symbols of the ions.

Ba 2+ Cl

 Balance the charges.

Ba 2+ Cl



Cl

 two Cl -

needed

Write the ionic formula using a

subscript 2

for two chloride ions.

BaCl 2

24

Examples Select the correct formula for each of the following ionic compounds.

A. Na + and O 2 1) NaO 2) Na 2 O 3) NaO 2 B. Mg 2+ and Cl 1) MgCl 2 C. Al 3+ and O 2 1) AlO 2) MgCl 2) Al 2 O 3 3) Mg 3) Al 3 2 O Cl 2 25

Chapter 4 Compounds and Their Bonds

4.3

Naming and Writing Ionic Formulas

26

Naming Ionic Compounds with Two Elements To name a compound that contains two elements, • • identify the

cation

and

anion

.

name the cation first, followed by the name of the anion with an –

ide

ending.

27

Charges of Representative Elements Copyright © 2009 by Pearson Education, Inc.

28

Names of Some Common Ions 29

Examples Complete the names of the following ions: Ca 2+ _________ N 3  _________ Al Se 3+ __________ 2  __________ P 3  S 2  _________ __________ Li + _________ F  _________ Br  _________ 30

Examples of Ionic Compounds with Two Elements

Formula Ions cation anion Name

NaCl K 2 S MgO CaI 2 Al 2 O 3 Na + K + Mg 2+ Ca 2+ Al 3+ Cl S 2 O 2 I O 2 sodium chloride potassium sulfide magnesium oxide calcium iodide aluminum oxide 31

Learning Check Write the formulas and names for compounds of the following ions: Br − S 2− N 3− Na + Al 3+ 32

Example Write the formula and names of the following compounds: 1) K + and Br 2) Ca 2+ and O 2 3) Al 3+ and S 2 4) Mg 2+ and F -

Transition Metals Form Positive Ions Most

transition metals and Group 4 (14) metals

form 2 or more positive ions. However, Zn 2+ , Ag + , and Cd 2+ form only one ion.

Metals That Form More Than One Cation The name of metals with two or more positive ions (cations) use a

Roman numeral

to identify ionic charge.

35

Naming Ionic Compounds with Variable Charge Metals 36

Naming Variable Charge Metals Transition metals with two different ions use a

Roman numeral

after the name of the metal to indicate ionic charge. 37

Naming FeCl 2 To name FeCl 2 : 1. Determine the charge of the cation using the charge of the anion (Cl ).

Fe ion + 2 Cl = Fe ion + 2- = 0 Fe ion =

2+

2. Name the cation by the element name and add a Roman numeral in parentheses to show its charge.

Fe

2+

= iron

(II)

3. Write the anion with an ide ending.

FeCl 2 = iron(II) chloride 38

Naming Cr 2 O 3 To name Cr 2 O 3 : 1. Determine the charge of cation from the anion (O 2 ).

2 Cr ions + 3 O 2 = 0 2 Cr ions + 3 (2-) = 0 2 Cr ions - 6 2 Cr ions Cr ion = 0 = 6+ =

3+ = Cr 3+

2. Name the cation by the element name and add a Roman numeral in parentheses to show its charge.

Cr

3+

= chromium

(III)

3. Write the anion with an ide ending.

chromium(III) oxide = Cr 2 O 3 39

Examples Select the correct name for each.

A. Fe 2 S 3 1) iron sulfide 2) iron(II) sulfide 3) iron(III) sulfide B. CuO 1) copper oxide 2) copper(I) oxide 3) copper(II) oxide 40

Guide to Writing Formulas from the Name Copyright © 2009 by Pearson Education, Inc.

41

Writing Formulas Write a formula for potassium sulfide.

1. Identify the cation and anion.

potassium = K + sulfide = S 2− 2. Balance the charges.

K + S 2− K + 2(1+) + 2(1-) = 0

3. 2 K + and 1 S 2− =

K 2 S

42

Writing Formulas Write a formula for iron(III) chloride.

1. Identify the cation and anion.

iron (III) = Fe 3+ (III = charge of 3+) chloride = Cl − 2. Balance the charges.

Fe 3+ Cl − Cl − = (3+) + 3(1-) = 0 Cl −

3. 1 Fe 3+ and 3 Cl − =

FeCl 3

43

Examples What is the correct formula for each of the following?

A. Copper(I) nitride 1) CuN 2) CuN 3 3) Cu 3 N B. Lead(IV) oxide 1) PbO 2 2) PbO 3) Pb 2 O 4 44