chapter 4 compounds and their bonds 4.1 octet rule and ions 1 copyright © 2009 by pearson...

Chapter 4 Compounds and Their Bonds

4.1 Octet Rule and Ions

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Copyright © 2009 by Pearson Education, Inc.

Octet RuleAn octet• is 8 valence electrons.• is associated with the stability of the noble

gases.

He is stable with 2 valence electrons (duet).

valence electrons

He 2 2

Ne 2, 8 8

Ar 2, 8, 8 8

Kr 2, 8, 14, 8 8

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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.

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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 ion 1+

Group 2A metals ion 2+

Group 3A metals ion 3+

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Formation of a Sodium Ion, Na+

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Charge of Sodium Ion, Na+

With the loss of its valence electron,

the sodium ion has a 1+ charge.

Na atom Na+ ion 11p+ 11p+

11e- 10e-

0 1+

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2, 8

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Formation of Mg2+

Magnesium achieves an octet by losing its two valence electrons.

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Charge of Magnesium Ion, Mg2+

With the loss of two valenceelectrons, magnesium forms

apositive ion with a 2+

charge.

Mg atom Mg2+ ion 12p+

12p+

12e- 10e-

0 2+

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Learning Check

A. The number of valence electrons in aluminum is1) 1e-. 2) 2e-. 3) 3e-.

B. The change in electrons for octet requires a1) loss of 3e-. 2) gain of 3e-. 3) a gain of 5e-.

C. The ionic charge of aluminum is1) 3-. 2) 5-. 3) 3+.

D. The symbol for the aluminum ion is1) Al3+. 2) Al3-. 3) Al+.

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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.

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Formation of a Chloride, Cl-

Chlorine achieves an octet by adding an electron to its valence electrons.

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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- 18e-

0 1–

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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-

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Some Ionic Charges

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Learning CheckA. The number of valence electrons in sulfur is

1) 4e-. 2) 6e-. 3) 8e-.

B. The change in electrons for octet requires a1) loss of 2e-. 2) gain of 2e-. 3) a gain of 4e-.

C. The ionic charge of sulfur is

1) 2+. 2) 2-. 3) 4-.

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Chapter 4 Compounds and Their Bonds

4.2Ionic Compounds

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Ionic CompoundsIonic 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.

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Salt Is An Ionic Compound

Sodium chloride or “table salt” is an example of an ionic compound.

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Ionic FormulasAn 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.

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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.

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Charge Balance in MgCl2

In MgCl2,

• 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.

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Charge Balance in Na2S

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In Na2S,

• 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.

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Writing Ionic Formulas from Charges

Charge balance is used to write the formula for

sodium nitride, a compound containing Na+ and N3−.

Na+

3 Na+ + N3− = Na3N

Na+

3(+1) + 1(3-) = 0

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Formula from Ionic Charges Write the ionic formula of the compound with Ba2+

and Cl.

• Write the symbols of the ions.

Ba2+ Cl

• Balance the charges.

Ba2+ Cl two Cl- needed Cl

• Write the ionic formula using a subscript 2 for

two chloride ions.

BaCl224

Learning CheckSelect the correct formula for each of the following ionic compounds.

A. Na+ and O2-

1) NaO 2) Na2O 3) NaO2

B. Al3+ and Cl-

1) AlCl3 2) AlCl 3) Al3Cl

C. Mg2+ and N3-

1) MgN 2) Mg2N3 3) Mg3N2

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Chapter 4 Compounds and Their Bonds

4.3Naming and Writing Ionic

Formulas

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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.

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Charges of Representative Elements

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Names of Some Common Ions

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Learning CheckComplete the names of the following ions: Ba2+ Al3+ K+

_________ __________ _________

N3 O2 F

_________ __________ _________

P3 S2 Cl _________ __________ _________

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Examples of Ionic Compounds with Two Elements Formula Ions Name

cation anion

NaCl Na+ Cl- sodium chloride

K2S K+ S2- potassium sulfide

MgO Mg2+ O2- magnesium oxide

CaI2 Ca2+ I- calcium iodide

Al2O3 Al3+ O2- aluminum oxide

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Learning CheckWrite the names of the following compounds:

1) CaO___________

2) KBr ___________

3) Al2O3___________

4) MgCl2 ___________

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Learning Check

Write the formulas and names for compounds of the following ions:

Br− S2− N3−

Na+

Al3+

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Transition Metals Form Positive Ions

Most transition metals and Group 4 (14) metals form 2 or more positive ions. However, Zn2+, Ag+, and Cd2+ 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.

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Naming Variable Charge Metals

Transition metals with two different ions use a Roman numeral after the name of the metal to indicate ionic charge.

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Naming FeCl2

To name FeCl2:1. Determine the charge of the cation using the

charge of the anion (Cl-).

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

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

Fe2+ = iron(II)3. Write the anion with an ide ending. FeCl2 = iron(II) chloride

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Naming Cr2O3To name Cr2O3:1. Determine the charge of cation from the anion

(O2-).2 Cr ions + 3 O2- = 02 Cr ions + 3 (2-) = 0 2 Cr ions - 6 = 02 Cr ions = 6+ Cr ion = 3+ = Cr3+

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

Cr3+ = chromium(III)3. Write the anion with an ide ending. chromium(III) oxide = Cr2O3

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Learning CheckSelect the correct name for each.A. Fe2S3

1) iron sulfide 2) iron(II) sulfide 3) iron(III) sulfide

B. CuO 1) copper oxide 2) copper(I) oxide 3) copper(II) oxide

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Writing FormulasWrite a formula for potassium sulfide.

1. Identify the cation and anion. potassium = K+

sulfide = S2−

2. Balance the charges. K+ S2−

K+

2(1+) + 2(1-) = 0

3. 2 K+ and 1 S2− = K2S

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Writing FormulasWrite a formula for iron(III) chloride.

1. Identify the cation and anion.

iron (III) = Fe3+ (III = charge of 3+)

chloride = Cl−

2. Balance the charges.

Fe3+ Cl−

Cl− = (3+) + 3(1-) = 0

Cl−

3. 1 Fe3+ and 3 Cl− = FeCl3

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Learning CheckWhat is the correct formula for each of the

following?

A. Copper(I) nitride

1) CuN 2) CuN3 3) Cu3N

B. Lead(IV) oxide

1) PbO2 2) PbO 3) Pb2O4

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