COVALENT BONDING

Chemistry Matter and Change Chapter 8

CHAPTER 8 MAIN IDEA

Covalent bonds form when atoms share electrons.

Atoms gain stability when

they share electrons and form covalent

bonds.

8.1

Main

Idea

REVIEW VOCABULARY & CONCEPTS

Chemical bondValence electronsElectronegativityLewis structure

NEW VOCABULARY & CONCEPTS

Covalent bondMoleculeSigma (σ)bondPi (π)bondEndothermic reactionExothermic reactionSingle bondDouble bondTriple bond

WHY DO ATOMS BOND?Sharing electrons takes less energy than being “alone”

Octet is usually the most stable electron configuration

WHAT IS A COVALENT BOND?

Shared pairs of electronshttp://www.glencoe.com/sites/

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SINGLE COVALENT BONDS Two atoms share one pair of electrons

Sigma bond (σ)Either : or _ for a Lewis Structure H H·+· ··H H or H-H

MULTIPLE COVALENT BONDS

Two atoms share more than one pair of electrons

One pair is a sigma bond (σ)the others are pi (π)bonds

Double bond shares 2 pair of electrons

Triple bond shares 3 pair of electrons

COMPARING BONDS

SingleCentereds orbital

electrons One pair of

electrons is shared

PairedParallel p orbital

electronsMultiple pairs

of electrons are shared

Sigma (σ) Bonds

Pi (π) Bonds

MOLECULEφ A neutral group of atoms joined together by covalent bonds.

DIATOMIC MOLECULESφ Molecules made up of two atoms.

φ There are 7 diatomic molecules.

φ H2, N2, O2, F2, Cl2, Br2, I2

Br I N Cl H O F

DIATOMIC MOLECULES

Oh, Ha Ha!

I couldn't exist

without you!

HYDROGEN

H· + ·H H:HHydrogen Hydrogen Hydrogen

Atom Atom molecule

φ The hydrogen molecule has a single covalent bond.

φ The electronegativity of each hydrogenatom is the same, so the electrons are shared.

Shared electron pair

MOLECULAR COMPOUNDS

φ Compounds comprised of molecules.

Ionic Compounds Molecular Compounds

Crystal Lattice Molecule

Types of Elements

Metal with non-metal or polyatomic ions

Non-metal with non-metal

Physical State

Solid Solid, liquid or gas

Melting Point High> 300 C

Low <300 C

Solubility in water

Generally high Generally low

Electrical conductivity of solution

Good conductor Poor to none

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LEWIS STRUCTURES AND OCTET

Practice by drawingH2

O2

N2

H2OCO2

+ +-

-

LEWIS STRUCTURES AND OCTET

Practice by drawingH2

+ +-

-

LEWIS STRUCTURES AND OCTET

Practice by drawing O2

++

-

--

-

-

-

-

-

- -

--

π

σ

+

-

- -

--

+-

-

-

-

---

STRENGTH OF COVALENT BONDS

Strength depends on distance of the atoms from each other

With more bonds comes stronger bonds

O2 is stronger than H2

single bond < Double

bond < Triple bond

22

CHEMICAL BONDS

23

CHEMICAL BONDSElectronegativity is an atom’s affinity

for electrons.

Differences in electronegativity dictate how electrons are distributed in covalent bonds.

- nonpolar covalent bonds = equal sharing of electrons

- polar covalent bonds = unequal sharing of electrons

BONDS AND ENERGYEndothermic reactions require additional energy for bonds to break

Exothermic reactions release energy when the bonds break (spontaneous)

NAMING MOLECULES

Section 8.2 Chemistry Matter & Change

Specific rules are used when

naming binary molecular

compounds, binary acids and

oxyacids

8.2

Main

Idea

OBJECTIVESTranslate molecular formulas into binary molecular names.

Name acidic solutions.

REVIEW VOCABULARY & CONCEPTS

Ionic bondCovalent bondFormula unitOxyanionNaming ionic substancesMolecule

NEW VOCABULARY & CONCEPTS

OxyacidBinary acid

NAMING BINARY MOLECULAR

COMPOUNDS1. Name the first element

using the entire name of the element.

2. The second element in the formula is named using the root and suffix “-ide.”

3. Prefixes are used to indicate the numbers of each element.

COMMON PREFIXESNumber of atoms

PrefixNumber of atoms

Prefix

1 Mono- 6 Hexa-2 Di- 7 Hepta-3 Tri- 8 Octa-4 Tetra- 9 Nona-5 Penta- 10 Deca-

NAMING BINARY MOLECULAR

COMPOUNDSExceptions to the rules:The first element never uses “mono-” There is an understood 1 if

nothing is specified.Awkward vowels can be dropped

NAMING BINARY MOLECULAR

COMPOUNDS EXCEPTION The first element never uses

“mono-” There is an understood 1 if

nothing is specified. CO2 is carbon dioxide not

monocarbon dioxide CO is carbon monoxide, not

monocarbon monoxide

PRACTICE NAMING BINARY COMPOUNDS

FORMULA SYSTEM NAME

N2O dinitrogen monoxide

NO nitrogen monoxide

N2O3 dinitrogen trioxide

NO2 nitrogen dioxide

N2O4 dinitrogen tetroxide

N2O5 dinitrogen pentoxide

NO3 nitrogen trioxide

NAMING BINARY ACIDSThe first word has the prefix “hydro-” followed by the root of the second element followed by “-ic”

The second word is “acid”HCl- hydrochloric acid

PRACTICE NAMING BINARY ACIDS

Hydrobromic acidHydrophosphic acidHydrosulfuric acidHFH2SeHI

NAMING OXYACIDSFirst word consists of the root of the

oxyanion (with prefixes if needed) followed by a suffix as specified

If oxyanion ends in

The second word is always “acid.”

Oxyanion ending New suffix for acid

-ate -ic

-ite -ous

NAMING OXYACIDSRelationship

General name

Oxyanion name

Example name

Example formula

One more oxygen than (root)ic

Per(root)ic acid Perchlorate Perchloric

acidHClO4

Root(ic) acid chlorate Chloric acid HClO3

One less oxygen than root(ic)

Root(ous) acid Chlorite Chlorous

acidHClO2

Two less oxygens than root(ic)

Hypo(root)ous acid

Hypochlorite

Hypochlorous acid HClO

NAMING OXYACIDSFirst word consists of the root of the

oxyanion (with prefixes if needed) followed by a suffix as specified

The second word is always “acid.”

Compound Oxyanion Acid suffix Acid name

HClO3 Chlorate -ic Chloric acid

HClO2 Chlorite -ous Chlorous acid

HNO3 Nitrate -ic Nitric Acid

HNO2 Nitrite -ous Nitrous Acid

Look at the formula of the

molecule

Is there oxygen present in the compound?

Hydro(root) ic acid

Root + -ic if the anion ends in –ate, or

Root + -ous if the anion ends in –ite, then

acid

Name the first element using a prefix if necessaryName the second element indicating the number of atoms and changing the

suffix to –ide.

YesNo

YesNo

Is it an acid?

Acid Formula Acid Name

H2CO3 Carbonic Acid

HBrO3 Bromic Acid

H2C Carbonic Acid

CH3COOH or CH3CO2H Acetic acid

H3PO4 Phosphoric acid

H2SO4 Sulfuric acid

H2SO3 Sulfurous Acid

PRACTICE NAMING OXYACIDS

CAN YOUTranslate molecular formulas into binary molecular names.

Name acidic solutions.

MOLECULAR STRUCTURE

Section 8.3 Chemistry Matter & Change

Structural formulas show

the relative positions of

atoms within a molecule.

8.3

Main

Idea

OBJECTIVESList the basic steps used to draw Lewis structures.

Explain why resonance occurs and identify resonance structures.

Identify three exceptions to the octet rule and name molecules in which these exceptions occur.

REVIEW VOCABULARY & CONCEPTS

Ionic bondCovalent bondLewis-dot structureOctet

NEW VOCABULARY & CONCEPTS

Structural formulaResonanceCoordinate covalent bondSpace filling modelBall and stick model

MOLECULAR STRUCTURES

Many different ways to depict the same thingMolecular formulaStructural formulaLewis StructureSpace-filling modelBall-and-stick model

MOLECULAR FORMULAIndicates number of each element in a molecule H2O C6H12O6

NH3

STRUCTURAL FORMULASMolecular model that shows the relative positions of the atoms

O H H

LEWIS STRUCTUREShows shared electrons and lone pairsShared pairs are usually

depicted as linesLone pairs may be lines or dots

SPACE-FILLING MODELAtoms are shown in relative size and position accounting for lone pairs

BALL AND STICK MODELSShow relative position of atoms and bondsEasier to see double and triple

bonds and bond angles

HINTS FOR LEWIS STRUCTURES

1. Carbon is usually in the middle

2. Group 1 and 17 elements are always at ends

3. Atoms that are less numerous are usually in the middle

(~Polyatomic Ions)

SIMPLE PRACTICE FOR LEWIS STRUCTURES

H2OHClCH3F

ORGANIC PRACTICE WITH LEWIS STRUCTURES

Methane CH4

Ethane C2H6

Propane C3H8

TRICKIER PRACTICECO2

HCNBH3

NH4+

TRICKIER ORGANIC PRACTICE

C2H6 ethaneC2H4 etheneC2H2 ethyne

RESONANCE STRUCTURES

More than one valid Lewis structure is possibleDiffer in position of electrons,

not position of atoms

HINTS FOR FORMING LEWIS STRUCTURES

Carbon is usually in the middle Group 1 and 17 elements are always at ends Atoms that are less numerous are usually in the

middle Hydrogen always forms one single bond Oxygen has two bonding electrons and two lone

pairs Nitrogen has three bonding electron and one lone

pair Group 13 elements have three bonding electrons

and zero lone pairs Elements in groups 1, 2, 13 may break octet by

having fewer electrons Phosphorus is a mess!

REALLY HARDPCl5SF6

ORGANIC CHEATS Common groups are often listed differently in organic molecules

Ex: we write NH2CH2COOH instead of C2NO2H5

CAN YOUList the basic steps used to draw Lewis structures.

Explain why resonance occurs and identify resonance structures.

Identify three exceptions to the octet rule and name molecules in which these exceptions occur.

MOLECULAR SHAPES

Section 8.4 Chemistry Matter and Change

The VSEPR model is used to

determine molecular shape

Main

Idea

OBJECTIVESSummarize VSEPR bonding theory

Predict the shape of, and bond angles in, a molecule

Define hybridization

REVIEW VOCABULARY & CONCEPTS

Atomic orbitals orbitalp orbital

NEW VOCABULARY & CONCEPTS

VSEPR theoryHybridizationTrigonal planarTrigonal pyramidalTetrahedralTrigonal bipyramidalLinearBentOctahedral

VSEPR MODELValence Shell Electron Pair Repulsion

Electrons repel each otherElectrons stay as far away from

each other as possibleLone pairs occupy more space than shared electrons

HYBRIDIZATIONOccurs because hybrid orbitals are more stable in some cases, notably carbon

Remodel the “hotel” to make the “rooms” equal

C: 1s22s22p2 1s22sp3

CARBON HYBRIDIZATION

GETTING STARTEDBegin with Lewis StructureStart with a tetrahedral and modify as needed

Remember to use 3-D space not 2-D space

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CH4: A TYPICAL TETRAHEDRAL

TETRAHEDRAL SHAPEFour atoms are coming from the center atom at equal angles

109.5° angle

TRIGONAL PYRAMIDALThree atoms coming from central atom and one lone pairBond angle 107°Lone pairs occupy more space

than shared pairs

BENTTwo atoms coming from central atom and two lone pairs

104.5° bond angle

SUMMARY OF COMMON MOLECULAR SHAPES

Molecule

Total pairs

Shared pairs

Lone pairs

Hybrid orbital

Molecular shape

BeCl2 2 2 0 sp Linear

AlCl3 3 3 0 sp2 Trigonal planar

CCl4 4 4 0 sp3 Tetrahedral

NH3 4 3 1 sp3 Trigonal pyramidal

H2O 4 2 2 sp3 Bent

NbBr5 5 5 0 sp3d Trigonal bipyramidal

SF6 6 6 0 sp3d2 Octahedral

TETRAHEDRAL BASED SHAPES

TetrahedralTrigonal Pyramidal

Bent

NON-TETRAHEDRAL BASED SHAPES

Linear Trigonal Planar

FEWER ELECTRONS THAN OCTET!

NON-TETRAHEDRAL BASED SHAPES

Trigonal Bipyramidal Octahedral

MORE ELECTRONS THAN OCTET!

CAN YOU…Summarize VSEPR bonding theory

Predict the shape of, and bond angles in, a molecule

Define hybridization

ELECTRONEGATIVITY AND POLARITY

Chapter 8.5 Chemistry Matter and Change

A chemical bond’s character is

related to each atom’s attraction for the electrons

in the bond.

Main

Idea

OBJECTIVESDescribe how electronegativity is used to determine bond type.

Compare and contrast polar and nonpolar covalent bonds and polar and nonpolar molecules

Generalize about the characteristics of covalently bonded compounds

REVIEW VOCABULARY & CONCEPTS

ElectronegativityElectron affinityIonic bondCovalent bond

NEW VOCABULARY & CONCEPTS

Polar covalent bondElectronegativity differenceMolecular polarityIntermolecular forcesSolubility Dipole

ELECTRON AFFINITY, ELECTRONEGATIVITY, AND BOND

CHARACTER

Electronegativity difference

Bond Character

> 1.7 Mostly ionic

0.4 - 1.7 Polar covalent

< 0.4 Mostly covalent

0 Nonpolar covalent

Electronegativity difference determines the character of the bond between atoms

Most bonds are partly ionic and partly covalentDiatomics are 100% covalent

BOND CHARACTER

IONIC BONDSCreated when the electronegativity difference is greater than 1.7

Elements are far apart on periodic tableExample: Na and Cl

Na = 0.9Cl = 3.0Difference is 2.1 ionic bondElectrons are transferred from Na to Cl

NON-POLAR COVALENT BONDS

Created when electronegativity difference is 0Usually atoms of the same

elementDiatomics

COVALENT BONDS Created when electronegativity difference is < 0.4

Elements are usually close together on the periodic table

IBr

POLAR-COVALENT BONDS

Created when electronegativity difference is between 0.4 and 1.7

Most bonds fall into this category

Electrons are shared unequallyH2O

POLAR COVALENT BONDS Molecules have a partial positive and a partial negative side

DIPOLE INTERACTIONS Reactions between oppositely charged ends of a polar molecule

POLAR COVALENT BONDSPolar bonds that are equal in all directions in a molecule create non-polar molecules

SOLUBILITY RULESLike dissolves like

Polar substances dissolve polar substances

Non-polar substances dissolve non-polar substances.

CAN YOUDescribe how electronegativity is used to determine bond type.

Compare and contrast polar and nonpolar covalent bonds and polar and nonpolar molecules

Generalize about the characteristics of covalently bonded compounds