Chemical Bonding

I. Introduction toBonding

2.4.1 Define chemical bond

2.4.2 Explain why most atoms form chemical bonds.

2.4.3 Describe ionic and covalent bonding.

2.4.4 Classify bonding type according to electronegativity differences

2.4.5 Define molecule and molecular formula.

OBJECTIVES OBJECTIVES

Review

We can also predict what ions an element will form.

+1

+2 +3

+/-

4 -3 -2 -10

multiple cations

Vocabulary

Chemical Bond

electrical attraction between nuclei and valence e- of neighboring atoms that binds the atoms together

bonds form in order to…increase stability

Vocabulary

Octet Rule:Atoms will transfer or share electrons in order to have 8 electrons in their highest energy level.

• This makes it like a noble gas

Vocabulary

CHEMICAL FORMULA

MolecularFormula

FormulaUnit

IONIC COVALENT

COCO22NaClNaCl

Vocabulary

COMPOUND

TernaryCompound

BinaryCompound

2 elementsmore than 2

elements

NaNONaNO33NaClNaCl

Vocabulary

ION

PolyatomicIon

MonatomicIon

1 atom 2 or more atoms

NONO33--NaNa++

IONIC COVALENTBond Formation

Type of Structure

Solubility in Water

Electrical Conductivity

OtherProperties

e- are transferred from metal to nonmetal

high

yes (solution or liquid)

yes

e- are shared between two nonmetals

low

no

usually not

MeltingPoint

crystal lattice true molecules

Types of Bonds

Physical State solid liquid or gas

“electron sea”

METALLICBond Formation

Type of Structure

Solubility in Water

Electrical Conductivity

OtherProperties

MeltingPoint

Types of Bonds

Physical State

e- are delocalized among metal atoms

very high

yes (any form)

no

malleable, ductile, lustrous

solid

Quick Hint

All All covalent bondscovalent bonds are between are between two non-metalstwo non-metals

All All ionic bondsionic bonds are between a are between a metalmetal (cation) and a (cation) and a nonmetalnonmetal (anion). (anion).

All All metallic bondsmetallic bonds are between are between two metalstwo metals

Lewis Structure

Covalent – show sharing of electronsIonic – show transfer of electrons

Lewis Structures

Covalent – show sharing of electronsIonic – show transfer of electrons

Ionic Nomenclature – Ionic Formulas

Write each ion, cation first. Don’t show charges in the final formula.

Overall charge must equal zero. If charges cancel, just write symbols. If not, use subscripts to balance charges.

Use parentheses to show more than one polyatomic ion.

Stock System – Roman numerals indicate the ion’s charge

Ionic Nomenclature – Ionic Names

Write the names of both ions, cation first.

Change ending of monatomic ions to –ide.

Polyatomic ions have special names.

Stock System – Use Roman numerals to show the ion’s charge if more than one is possible. Overall charge must equal zero.

Ionic Nomenclature

Consider the following: Does it contain a polyatomic ion?

-ide, 2 elements no-ate or –ite, 3+ elements yes

Does it contain a Roman numeral?Check the table for metals not in Groups 1 or 2.

No prefixes.

Ionic Nomenclature

Potassium chloride K+ Cl- KCl

Magnesium nitrate Mg2+ NO- Mg(NO3)2

Copper (ii) chloride Cu2+ Cl- CuCl2

Ionic Nomenclature

NaBr Sodium bromide

Na2CO3

Sodium carbonate

FeCl3 Iron (III) chloride

Covalent Bonding

• Covalent bonds can have multiple bonds.• Single Covalent Bond

– Chemical bond resulting from sharing of an electron pair between two atoms

Double Covalent Bond Chemical bond resulting from sharing of

two electron pairs between two atoms

Triple Covalent Bonds Chemical bond resulting from sharing of

three electron pairs between two atoms

Molecular Nomenclature

Prefix System (Binary system)

1.Less electronegative atom comes first.

2.Add prefixes to indicate number of atoms. Omit mono- prefix on first element.

3.Change the ending of the second element to –ide.

Molecular Nomenclature Prefixes

Mono- 1Di- 2Tri- 3Tetra- 4Penta- 5

Hexa- 6Hepta- 7Octa- 8Nona- 9Deca- 10

Molecular Nomenclature

CCl4 Carbon tetrachloride

N2O

Dinitrogen monoxideSF6

Sulfur hexaflouride

Molecular Nomenclature

Arsenic trichloride AsCl3

Dinitrogen monoxide N2O5

Tetraphosphorus decoxide P4O10

Bond Polarity

Most bonds are a blend of ionic and covalent characteristics.

Differences in electronegativity determines bond type.

Bond Polarity

Electronegativity Attraction an atom has for a shared pair

of electrons. higher e-neg atom -

lower e-neg atom +

Dipole Movement

Dipole Moment - a measure of the polarity of a bond. Is often represented by a special arrow. Arrow points to more EN atom.

Bond Polarity

Electronegativity Trend (p. 151) Increases up and to the right.

Nonpolar Covalent Bond e- are shared equally symmetrical e- density usually identical atoms

Bond Polarity

+ -

Bond Polarity

Polar Covalent Bond e- are shared unequally asymmetrical e- density results in partial charges (dipole)

Bond Polarity

Ionic Bond e- are not shared results in charged particles opposite charges attract

Determining Type, EN0.3

1.7

5% 50%

Determining Type, EN

Ionic, Polar or Nonpolar Covalent Compounds: The difference in electronegativity between bonding atoms leads to the type of compound.

Example:O2 , O=O ENO = 3.5 EN = 0 NO , N=O ENN = 3.0, ENO = 3.5 EN = .5 CO , C= ENC = 2.5, ENO = 3.5 EN = 1.0 NaCl , Na+Cl- ENNa = 0.9, ENCl = 3.0 EN = 2.1

Nonpolar Covalent

Polar Covalent

Ionic

Polar Covalent

Sample Problem

Use electronegativity differences to classify bonding between sulfur, S, and the following elements: hydrogen, H; cesium, Cs; and chlorine, Cl. In each pair, which atom will be more negative?Bonding between sulfur and

Electronegativity difference Bond

type

More-negative atom

hydrogen 2.5 – 2.1 = 0.4 Polar-covalent

sulfur

cesium 2.5 – 0.7 = 1.8 Ionic sulfur

chlorine 3.0 – 2.5 = 0.5 Polar-covalent

chlorine

Additional Sample Problems

Complete the following chart:

Elements bonded

Electronegativity difference Bond

type

More-negative atom

a. C and H 2.5 – 2.1 = 0.4 Polar-covalent

carbon

b. C and S 2.5 – 2.5 = 0 Nonpolar covalent

Same electronegativityc. O and H 3.5 – 2.1 = 1.4 Polar-

covalentoxygen

d. Na and Cl

3.0 – 0.9 = 2.1 Ionic chlorine

e. Cs and S

2.5 – 0.7 = 1.8 Ionic sulfur