Unit 7: Chemical Bonding

Colossians 1:9For this reason, since the day we

heard about you, we have not stopped praying for you and asking God to fill you with the knowledge of his will through all spiritual wisdom and understanding.

Objective 1To learn about ionic and covalent bonds and explain how they are formed.

Objective 2To learn about stable electron

configurations.To learn to predict the formulas for

ionic compounds.

Chemical bondsA bond is a force that holds groups

of two or more atoms together and makes them function as a unit.

There are three types of bonds:IonicCovalentmetallic

IonicTransfer of electrons occur from the

metal to the nonmetal to form a + and - ion.

The bond is the electrostatic attraction between the opposite charges.

Electronegativity difference is greater than 1.67

IonicSolids are nonconductors.When melted as a liquid, dissolved

in water or as a gas they are conductors.

High melting points and boiling points

Brittle, low volatility, low vapor pressure

Covalent bondingNo electron transfer.A pair of electrons is shared

between the atoms. Usually between nonmetals.One pair shared forms a single bond.Two pairs shared, double bond.Three pairs shared, triple bond.

Covalent BondingElectronegativity difference less

than 1.67Nonconductors of electricityNon-electrolytesLow melting points & boiling pointsVolatile (form fumes)

Metallic bondingOnly in metals.Called the electron sea model.+ ions in a sea of free electrons.Metals are made of closely packed

+ ions rather than neutral atoms.The cations are surrounded by

mobile valence electrons.

Metallic bonding

MetalsConductors of heat and electricity.High melting points and boiling

pointsHave a lusterMalleable, ductile

Objective 3To understand the nature of bonds and their relationship to electronegativity.

ElectronegativityThe relative tendency of an atom

to attract electrons to itself when bonded to another atom.

Elements are assigned an electronegativity value based on experimental tests.

Bond characterElectrons will transfer between

atoms when the difference between the electronegativities is very high. (ionic bond)

If they have similar electronegativities we would predict they would share electrons. (covalent bond)

Bond TypeEN diff C or I? EN diff C or I?

Al-Si B-NaBr-Rb Ca-ClBa-N Na-SMg-O N-SrCa-P F-S

To form a chemical compound, all atoms achieve a noble gas configuration.

In ionic bonding the attraction of opposite charges holds the compound together

Ionic compoundsDot diagrams of atoms on the leftShow the transfer of electronsIons formed on the right

Ionic compoundsBr-RbBa-NMg-OCa-Cl

Ionic solidsForm a crystal lattice where the

ions act like spheres that attract throughout the structure.

+ ions being smaller than – ions.

LiCl

You try:Li-OSr-OAl-O

Complete WS Ionic

Objective 4To learn to write Lewis Structures.

Objective 5To learn about the nonpolar and

polar covalent bond.

Objective 6To understand bond polarity and how it is related to molecular polarity.

Objective 7To understand molecular structure and bond angles.

H2

Electronegativity difference= 0Two s orbitals overlap to form a

nonpolar covalent bond.The molecular shape is linear.Bond angle is 180o.A sigma covalent bond has been

formed.

Sigma bondOverlap between two s orbitals.Overlap between an s and p

orbital.Overlap between two p orbitals,

head-to-head.

Cl2Two p orbitals overlap to form a

nonpolar covalent bond.A sigma bond has formed.The molecular shape is linear.The bond angle is 180o.

O2

A double bond is formed between the two atoms.

A sigma bond forms first between p orbitals “head-to-head.”

A bond forms between two p orbitals with overlap in a parallel fashion.

Nonpolar covalent bond. Molecular shape-linear

Bond angle 180o.

N2

A triple bond forms between the two atoms.

A sigma and then two pi bonds.The bond is a nonpolar covalent

bond. Molecular shape is linear.Bond angle 180o.

HClFind electronegativity difference.The covalent bond is polar. The

electron pair is not shared equally. A partially positive and partially negative is formed.

The molecule is polar. Molecular shape is linear with a bond angle of 180o.

H2SCovalent bond- polarMolecule-polarMolecular shape- V or bentBond angle- 92o

PH3

Covalent bond- polarMolecule- polarMolecular shape- Trigonal pyramidBond angle- 93o

Objective 8To learn to predict molecular geometry from the number of electron pairs.

VSEPR TheoryValence Shell Electron Pair

Repulsion TheoryStructure is determined by

minimizing the repulsion between electron pairs.

Bonding and nonbonding pairs repel as far apart as possible

CH4

Hybridization- blending of orbitals to make new orbitals of equal energy.

Four pairs of electrons around the central atom.

Type hybrid- sp3

CH4

CH4

Covalent bond- polarMolecule- nonpolarType hybrid- sp3

Orbital shape- tetrahedralMolecular shape- tetrahedralBond angle- 109.5o

NH3

3 bonding pairs, 1 unshared pairBond- polarMolecule- polarOrbital shape- tetrahedralMolecular shape- trigonal pyramidType hybrid- sp3

Bond angle- 107o

Ammonia

TermsBond polar- if different atoms share

the electron pair.Bond nonpolar- same element shares

the electron pair.Polar molecule- poles, bonded &

unbonded pairs existNonpolar molecule- no poles, all the

same all the way around.

H2O, sp3 hybridTwo bonding pairsTwo unshared pairsBond-polarMolecule- polarOS- tetrahedralMS- V or bentBond angle 104.5o

H2O

sp3

Bond Lone OS MS AngleCH4 4 0 Tetrahedral Tetrahedral 109.5NH3 3 1 Tetrahedral Trigonal pyramid 107H2O 2 2 Tetrahedral V or bent 104.5

HF1:3 1 shared pair, 3 unshared

electron pairsType hybrid- sp3

Polar bond, polar moleculeOrbital shape: tetrahedralMolecular shape: linearBond angle- 180o

BF3

Type hybrid- sp2

3 pairs around the central element.Be, Mg and Boron family all

exceptions to octet rule.Bond- polar Molecule- nonpolarOS & MS Trigonal planar, 120o

sp2

Bond Lone OS MS AngleBF3 3 0 Trigonal planar Trigonal planar 120AB2 2 1 Trigonal planar V or bent 118AB 1 2 Trigonal planar Linear 180

BeCl2, sp hybridTwo pairs around central atom.Bond- polar Molecule- NPOrbital Shape- linearMolecular shape- linearBond angle- 180o

spBond Lone OS MS Angle

BeCl2 2 0 Linear Linear 180

Objective 9To learn to apply the VSEPR model to molecules with double bonds.

Type hybrid?C2H6

C2H4

C2H2

DrawC3H6O2

IsomersHave the same molecular formula,

but different structural formulas.Draw two isomers of C4H10.

IsomersHow many isomers can you draw

for C3H6Cl2?

Polyatomic ionsDraw SO4

-2

Draw H2SO4

TermsCoordinate covalent bond- the

sharing of a pair of electrons, but both electrons come from one atom. Oxygen does this a lot.

Polyatomic ionsNH4

+, SO4-2

Are held together by covalent bonds.

End up with an ion with a charge.(NH4)2SO4

You try:OH-

PO4-3

ResonanceResonance exists when there is

more than one dot diagram to represent a structure.

Draw the resonance structures for NO3

-

ResonanceDraw the resonance hybrids for

benzene, C6H6.

Good to know:Never double bond to a halogen.Put an element in the middle and

bond onto it symmetrically around.Do not string elements like S to O

to O to O. Put the S in the middle and put the O’s around it.

Try to give each element an octet.