Chapter 4 Compounds and Their Bondschemvision.net/10_Chapter4_Timberlake.pdfFormation of Negative...

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Chapter 4 Compounds and Their Bonds

4.1 Octet Rule and Ions

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An octet• is 8 valence electrons.• is associated with the stability of the noble gases.

He is stable with 2 valence electrons (duet).

valence electronsHe 2 2Ne 2, 8 8Ar 2, 8, 8 8Kr 2, 8, 14, 8 8

Octet Rule

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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+

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+ ion12p+ 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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Solution

A. The number of valence electrons in aluminum is3) 3 e-.

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

C. The ionic charge of aluminum is3) 3+.

D. The symbol for the aluminum ion is1) Al3+.

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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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A. The number of valence electrons in sulfur is1) 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 is1) 2+. 2) 2-. 3) 4-.

Learning Check

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A. The number of valence electrons in sulfur is2) 6e-.

B. The change in electrons for octet requires a2) gain of 2e-.

C. The ionic charge of sulfur is2) 2-.

Solution

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Chapter 4 Compounds and Their Bonds

4.2Ionic Compounds

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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.

Ionic Compounds

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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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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.

Ionic Formulas

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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

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. Copyright © 2009 by Pearson Education, Inc.

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Writing Ionic Formulas from Charges

Charge balance is used to write the formula forsodium nitride, a compound containing Na+ and N3−.

Na+

3 Na+ + N3− = Na3NNa+

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

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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. BaCl2

Formula from Ionic Charges

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Select 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

Learning Check

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A. Na+ and O2-

2) Na2O check: 2Na+ + O2- = 2(1+) + 1(2-) = 0

B. Al3+ and Cl-1) AlCl3

check: Al3+ + Cl- = (3+) + 3(1-) = 0

C. Mg2+ and N3-

3) Mg3N2 check: 2Mg2+ +2N3- = 2(3+) + 2(3-) = 0

Solution

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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 cationand 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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Complete the names of the following ions:

Ba2+ Al3+ K+

_________ __________ _________

N3− O2− F−

_________ __________ _________

P3− S2− Cl−_________ __________ _________

Learning Check

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Ba2+ Al3+ K+

barium aluminum potassium

N3− O2− F−

nitride oxide fluoride

P3− S2− Cl−phosphide sulfide chloride

Solution

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Formula Ions Namecation anion

NaCl Na+ Cl- sodium chlorideK2S K+ S2- potassium sulfideMgO Mg2+ O2- magnesium oxideCaI2 Ca2+ I- calcium iodideAl2O3 Al3+ O2- aluminum oxide

Examples of Ionic Compounds with Two Elements

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Write the names of the following compounds:

1) CaO ___________

2) KBr ___________

3) Al2O3 ___________

4) MgCl2 ___________

Learning Check

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Write the names of the following compounds:

1) CaO calcium oxide2) KBr potassium bromide3) Al2O3 aluminum oxide4) MgCl2 magnesium chloride

Solution

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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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Solution

Br− S2− N3−

Na+

Al3+

NaBrsodium bromide

Na2Ssodium sulfide

Na3Nsodium nitride

AlBr3aluminum bromide

Al2S3aluminum sulfide

AlNaluminum nitride

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.

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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 Ionic Compounds with Variable Charge Metals

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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 aRoman 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 Cr2O3

To 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 aRoman 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 Check

Select the correct name for each.A. Fe2S3

1) iron sulfide2) iron(II) sulfide3) iron(III) sulfide

B. CuO1) copper oxide2) copper(I) oxide 3) copper(II) oxide

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Solution

Select the correct name for each.A. Fe2S3

3) iron (III) sulfide Fe3+ S2-

B. CuO3) copper (II) oxide Cu2+ O2-

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Guide to Writing Formulas from the Name

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Writing Formulas

Write 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 Formulas

Write 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-) = 0Cl−

3. 1 Fe3+ and 3 Cl− = FeCl3

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Learning Check

What is the correct formula for each of the following?A. Copper(I) nitride

1) CuN 2) CuN3 3) Cu3N

B. Lead(IV) oxide1) PbO2 2) PbO 3) Pb2O4

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Solution

The correct formula isA. Copper(I) nitride

3) Cu3N Need 3 Cu+ and N3-

B. Lead(IV) oxide1) PbO2 Need Pb4+ and 2 O2-

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4.4 Polyatomic Ions

Chapter 4 Compounds and Their Bonds

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A polyatomic ion• is a group of atoms. • has an overall ionic charge.

Some examples of polyatomic ions areNH4

+ ammonium OH− hydroxideNO3

− nitrate NO2− nitrite

CO32− carbonate PO4

3− phosphateHCO3

− hydrogen carbonate(bicarbonate)

Polyatomic Ions

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Some Compounds with Polyatomic Ions

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The names of common polyatomic anions • end in ate.

NO3− nitrate PO4

3− phosphate• with one oxygen less end in ite.

NO2− nitrite PO3

3− phosphite• with hydrogen attached use the prefix hydrogen (or bi).

HCO3− hydrogen carbonate (bicarbonate)

HSO3− hydrogen sulfite (bisulfite)

Some Names of Polyatomic Ions

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Names and Formulas of Common Polyatomic Ions

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• The positive ion is named first, followed by the name of the polyatomic ion.

NaNO3 sodium nitrateK2SO4 potassium sulfateFe(HCO3)3 iron(III) bicarbonate

or iron(III) hydrogen carbonate(NH4)3PO3 ammonium phosphite

Naming Compounds with Polyatomic Ions

Guide to Naming Compounds with Polyatomic Ions

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Some Compounds with Polyatomic Ions

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Match each formula with the correct name.

A. MgS 1) magnesium sulfite MgSO3 2) magnesium sulfateMgSO4 3) magnesium sulfide

B. Ca(ClO3)2 1) calcium chlorateCaCl2 2) calcium chloriteCa(ClO2)2 3) calcium chloride

Learning Check

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Match each formula with the correct name.

A. MgS 3) magnesium sulfideMgSO3 1) magnesium sulfite MgSO4 2) magnesium sulfate

B. Ca(ClO3)2 1) calcium chlorateCaCl2 3) calcium chlorideCa(ClO2)2 2) calcium chlorite

Solution

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Learning Check

Name each of the following compounds:

A. Mg(NO3)2

B. Cu(ClO3)2

C. PbO2

D. Fe2(SO4)3

E. Ba3(PO3)2

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Solution

Name each of the following compounds:

A. Mg(NO3)2 magnesium nitrateB. Cu(ClO3)2 copper(II) chlorateC. PbO2 lead(IV) oxideD. Fe2(SO4)3 iron(III) sulfateE. Ba3(PO3)2 barium phosphite

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Writing Formulas with Polyatomic Ions

The formula of an ionic compound • containing a polyatomic ion must have a charge

balance that equals zero (0).Na+ and NO3

− -> NaNO3

• with two or more polyatomic ions has the polyatomic ions in parentheses.Mg2+ and 2NO3

− -> Mg(NO3)2

subscript 2 for charge balance

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Select the correct formula for each.A. aluminum nitrate

1) AlNO3 2) Al(NO)3 3) Al(NO3)3

B. copper(II) nitrate1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3)

C. iron(III) hydroxide1) FeOH 2) Fe3OH 3) Fe(OH)3

D. tin(IV) hydroxide1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)

Learning Check

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Select the correct formula for each.

A. aluminum nitrate 3) Al(NO3)3

B. copper(II) nitrate 2) Cu(NO3)2

C. iron(III) hydroxide 3) Fe(OH)3

D. tin(IV) hydroxide 1) Sn(OH)4

Solution

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Learning Check

Write the correct formula for each.

A. potassium bromateB. calcium carbonateC. sodium phosphateD. iron(III) oxideE. iron(II) nitrite

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Solution

Write the correct formula for each.A. potassium bromate KBrO3

B. calcium carbonate CaCO3

C. sodium phosphate Na3PO4

D. iron(III) oxide Fe2O3

E. iron(II) nitrite Fe(NO2)2

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Flowchart for Naming Ionic Compounds

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Learning Check

Name the following compounds:A. Ca3(PO4)2

B. FeBr3

C. Al2S3

D. Zn(NO2)2

E. NaHCO3

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Solution

Name the following compounds:A. Ca3(PO4)2Ca2+ PO4

3− calcium phosphateB. FeBr3 Fe3+ Br − iron(III) bromideC. Al2S3 Al3+ S2− aluminum sulfideD. Zn(NO2)2 Zn2+ NO2

− zinc nitriteE. NaHCO3 Na+ HCO3

− sodium hydrogen carbonateor sodium bicarbonate

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Learning Check

Write the formulas for the following:A. calcium nitrate

B. iron(II) hydroxide

C. aluminum carbonate

D. copper(II) bromide

E. lithium phosphate

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Solution

Write the formulas for the following:A. calcium nitrate Ca2+, NO3

− Ca(NO3)2

B. iron(II) hydroxide Fe2+, OH− Fe(OH)2

C. aluminum carbonate Al3+, CO32− Al2(CO3)3

D. copper(II) bromide Cu2+, Br− CuBr2

E. lithium phosphate Li+, PO43− Li3PO4

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Chapter 4 Compounds and Their Bonds

4.5Covalent Compounds

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Covalent bonds form

• when atoms share electrons to complete octets.

• between two nonmetal atoms.

• between nonmetal atoms from Groups 4A (14), 5A (15), 6A (16), and 7A (17).

Covalent Bonds

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Hydrogen Molecule

A hydrogen molecule

• is stable with 2 electrons (helium).

• has a shared pair of electrons.

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Forming Octets in Molecules

In a fluorine, F2,, molecule, each F atom

• shares 1 electron.

• attains an octet.

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Carbon Forms 4 Covalent Bonds

In a CH4 (methane) molecule,

• 1 C atom shares electrons with 4 H atoms to attain an octet.

• each H atom shares 1 electron to become stable, like helium.

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Multiple Bonds

In a nitrogen molecule, N2,

• each N atom shares 3 electrons.• each N attains an octet.• the bond is a multiple bond called a triple bond.• the name is the same as the element.

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Naming Covalent Compounds

In the names of covalent compounds, prefixes are used to indicate the number of atoms (subscript) of each element. (mono is usually omitted)

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Guide to Naming Covalent Compounds

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What is the name of SO3?

1. The first nonmetal is S sulfur. 2. The second nonmetal is O, named oxide.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

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Name P4S3.

1. The first nonmetal, P, is phosphorus. 2. The second nonmetal, S, is sulfide.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

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Formulas and Names of Some Covalent Compounds

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Select the correct name for each compound.A. SiCl4 1) silicon chloride

2) tetrasilicon chloride3) silicon tetrachloride

B. P2O5 1) phosphorus oxide2) phosphorus pentoxide3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide2) dichlorine oxide3) chlorine heptoxide

Learning Check

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Select the correct name for each compound.

A. SiCl4 3) silicon tetrachlorideB. P2O5 3) diphosphorus pentoxideC. Cl2O7 1) dichlorine heptoxide

Solution

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Write the name of each covalent compound.

CO _____________________CO2 _____________________PCl3 _____________________CCl4 _____________________N2O _____________________

Learning Check

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Write the name of each covalent compound.

CO carbon monoxideCO2 carbon dioxidePCl3 phosphorus trichlorideCCl4 carbon tetrachlorideN2O dinitrogen oxide

Solution

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Guide to Writing Formulas for Covalent Compounds

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Write the formula for carbon disulfide.

STEP 1: Elements are C and SSTEP 2: No prefix for carbon means 1 C

Prefix di = 2Formula: CS2

Example: Writing Formulas for Covalent Compounds

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Write the correct formula for each of the following:

A. phosphorus pentachloride

B. dinitrogen trioxide

C. sulfur hexafluoride

Learning Check

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Write the correct formula for each of the following:

A. phosphorus pentachloride 1 P penta = 5 Cl PCl5

B. dinitrogen trioxidedi = 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 itscorrect name.

A. SO3

B. BaCl2C. (NH4)3PO3

D. Cu2CO3

E. N2O4

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Study Tip: Ionic or Covalent

A compound is• ionic if the first element in the formula

or the name is a metal or the polyatomic ion NH4+ .

K2O K is a metal; compound is ionic; potassium oxide

• covalent if the first element in the formula or the name is a nonmetal.

N2O N is a nonmetal; compound is covalent; dinitrogen oxide

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Solution

Identify each compound as ionic or covalent and give itscorrect name.

A. SO3 covalent – sulfur trioxideB. BaCl2 ionic – barium chlorideC. (NH4)3PO3 ionic – ammonium phosphiteD. Cu2CO3 ionic – copper(I) carbonateE. N2O4 covalent – dinitrogen tetroxide

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Learning Check

Identify each compound as ionic or covalent and give itscorrect name.

A. Ca3(PO4)2B. FeBr3

C. SCl2D. Cl2OE. N2

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Solution

Identify each compound as ionic or covalent and give itscorrect name.

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

B. FeBr3 ionic Fe3+ Br − iron(III) bromideC. SCl2 covalent 1S 2 Cl sulfur dichlorideD. Cl2O covalent 2 Cl 1 O dichlorine oxideE. N2 covalent element nitrogen

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Learning Check

Determine if each is ionic (I) or covalent (C ), and write the formula.

A. calcium nitrate

B. boron trifluoride

C. aluminum carbonate

D. dinitrogen tetroxide

E. copper(I) phosphate

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Solution

Determine if each is ionic (I) or covalent (C ), and write the formula.

A. calcium nitrate (I) Ca2+, NO3− Ca(NO3)2

B. boron trifluoride (C) 1 B, 3 F BF3

C. aluminum carbonate (I) Al3+, CO32− Al2(CO3) 3

D. dinitrogen tetroxide (C) 2 N, 4 O N2O4

E. copper(I) phosphate (I) Cu+, PO43− Cu3PO4

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Chapter 4 Compounds and Their Bonds

4.6 Electronegativity and Bond Polarity

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The electronegativity value

• indicates the attraction of an atom for shared electrons.

• increases from left to right going across a period on the periodic table.

• is high for the nonmetals, with fluorine as the highest.

• is low for the metals.

Electronegativity

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Some Electronegativity Values for Group A Elements

Low values

High values

`Electronegativity increases

`E

lectronegativity decreases

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104

A nonpolar covalent bond

• occurs between nonmetals.• is an equal or almost equal sharing of electrons.• has almost no electronegativity difference (0.0 to 0.4).

Examples: Electronegativity

Atoms Difference Type of BondN-N 3.0 - 3.0 = 0.0 Nonpolar covalentCl-Br 3.0 - 2.8 = 0.2 Nonpolar covalentH-Si 2.1 - 1.8 = 0.3 Nonpolar covalent

Nonpolar Covalent Bonds

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A polar covalent bond

• occurs between nonmetal atoms.• is an unequal sharing of electrons.• has a moderate electronegativity difference (0.5 to 1.7).

Examples: Electronegativity

Atoms Difference Type of BondO-Cl 3.5 - 3.0 = 0.5 Polar covalentCl-C 3.0 - 2.5 = 0.5 Polar covalentO-S 3.5 - 2.5 = 1.0 Polar covalent

Polar Covalent Bonds

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Comparing Nonpolar and Polar Covalent Bonds

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107

Ionic Bonds

An ionic bond• occurs between metal and nonmetal ions.• is a result of electron transfer.• has a large electronegativity difference (1.8 or more).

Examples: Electronegativity

Atoms Difference Type of BondCl-K 3.0 – 0.8 = 2.2 IonicN-Na 3.0 – 0.9 = 2.1 IonicS-Cs 2.5 – 0.7 = 1.8 Ionic

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Electronegativity and Bond Types

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Predicting Bond Types

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Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following:

A. K-NB. N-OC. Cl-ClD. H-Cl

Learning Check

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Use the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following:

A. K-N 2.2 ionic (I) B. N-O 0.5 polar covalent (P)C. Cl-Cl 0.0 nonpolar covalent (NP) D. H-Cl 0.9 polar covalent (P)

Solution

112

Chapter 4 Compounds and Their Bonds

4.7Shapes and Polarity of Molecules

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°

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VSEPR

In the valence-shell electron-pair repulsion theory(VSEPR), the electron groups around a central atom

• are arranged as far apart from each other as possible.

• have the least amount of repulsion of the negatively charged electrons.

• have a geometry around the central atom that determines molecular shape.

Guide to Predicting Molecular Shape

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Four Electron Groups

In a molecule of CH4,• there are 4 electron groups

around C. • repulsion is minimized by

placing 4 electron groups at angles of 109°, which is a tetrahedral arrangement.

• the shape with four bonded atoms is tetrahedral.

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116

Three Bonding Atoms and One Lone Pair

In a molecule of NH3,• 3 electron groups bond to H atoms, and the fourth one

is a lone (nonbonding) pair.• repulsion is minimized with 4 electron groups in a

tetrahedral arrangement.• with 3 bonded atoms, the shape is pyramidal.

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Two Bonding Atoms and Two Lone Pairs

In a molecule of H2O,• 2 electron groups are bonded to H atoms and 2 are lone

pairs (4 electron groups).• 4 electron groups minimize repulsion in a tetrahedral

arrangement.• the shape with 2 bonded atoms is bent.

Electron Pairs

Bonded Atoms

Lone Pairs

Molecular Shape

Example

4 4 0 Tetrahedral CH4

4 3 1 Pyramidal NH3

4 2 2 Bent H2O

Shapes with 4 Electron Groups

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119

Learning Check

State the number of electron groups, lone pairs, and use VSEPR theory to determine the shape of the following molecules or ions.1) tetrahedral 2) pyramidal 3) bent

A. PF3

B. H2SC. CCl4

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Study Tip

To determine shape, 1. draw the electron-dot structure.2. count the electron pairs around the central atom.3. count the bonded atoms to determine shape.

4 electron pairs and 4 bonded atoms = tetrahedral4 electrons pairs and 3 bonded atoms = pyramidal4 electron pairs and 2 bonded atoms = bent

121

Solution

A. PF3

4 electron groups, 1 lone pair, (2) pyramidalB. H2S

4 electron groups, 2 lone pairs, (3) bentC. CCl4

4 electron groups, 0 lone pairs, (1) tetrahedral

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Polar Molecules

A polar molecule• contains polar bonds.• has a separation of positive and negative charge

called a dipole, indicated with δ+ and δ-.• has dipoles that do not cancel.

δ+ δ-• •

H–Cl H—N—Hdipole

Hdipoles do not cancel

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Nonpolar Molecules

A nonpolar molecule• contains nonpolar bonds.

Cl–Cl H–H

• or has a symmetrical arrangement of polar bonds.O=C=O Cl

Cl–C–Cl

Cldipoles cancel

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Determining Molecular Polarity

STEP 1: Write the electron-dot formula.STEP 2: Determine the shape.STEP 3: Determine if dipoles cancel or not.

Example: H2O. .

H O: H2O is polar

Hdipoles do not cancel

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Learning Check

Identify each of the following molecules as 1) polar or 2) nonpolar. Explain.

A. PBr3B. HBrC. Br2D. SiBr4

126

Solution

Identify each of the following molecules as 1) polar or 2) nonpolar. Explain.

A. PBr3 1) pyramidal; dipoles do not cancel; polar

B. HBr 1) linear; one polar bond (dipole); polar

C. Br2 2) linear; nonpolar bond; nonpolar

D. SiBr4 2) tetrahedral; dipoles cancel; nonpolar