The Chemical BondThe Chemical Bond

Chemical BondsChemical Bonds

Are the forces that hold atoms together to Are the forces that hold atoms together to form compoundsform compounds

Bond energy – the amount of energy Bond energy – the amount of energy needed to break a bond and produce a needed to break a bond and produce a neutral atomneutral atom

Bond strength – the amount of force Bond strength – the amount of force holding two atoms togetherholding two atoms together Ex. 85.9 kcal/moleEx. 85.9 kcal/mole

Types of BondsTypes of Bonds

Ionic Bond – involves the transfer of electrons Ionic Bond – involves the transfer of electrons between atomsbetween atoms

Covalent Bond – involves that sharing of Covalent Bond – involves that sharing of electrons between atomselectrons between atoms Types of Covalent bondsTypes of Covalent bonds

• Single C:CSingle C:C• Double C::CDouble C::C• Triple C:::CTriple C:::C

Coordinate Covalent Bond – one atoms donates Coordinate Covalent Bond – one atoms donates a pair of electrons to be shareda pair of electrons to be shared

Ionic BondsIonic Bonds

Involves electron transfer and ion formationInvolves electron transfer and ion formation Cation – has a positive chargeCation – has a positive charge Anion – has a negative chargeAnion – has a negative charge The cation is much smaller than the anionThe cation is much smaller than the anion In an ionic solid ions pack together in a way that In an ionic solid ions pack together in a way that

is dependant of the size of the ionsis dependant of the size of the ions Ions arrange in a way that there is local Ions arrange in a way that there is local

neutralityneutrality High melting point crystalline solidsHigh melting point crystalline solids

Electron Transfer / Ion FormationElectron Transfer / Ion Formation

Ionic BondIonic Bond

Metallic BondsMetallic Bonds

The force of attraction that holds metals The force of attraction that holds metals togethertogether

It consists of the attraction of free-floating It consists of the attraction of free-floating valence electrons for positively charged valence electrons for positively charged metal ionsmetal ions

MetalsMetals

The valence electrons of metal atoms can The valence electrons of metal atoms can be modeled as a sea of electronsbe modeled as a sea of electrons

Properties of MetalsProperties of Metals(due to the ‘sea’ of electrons)(due to the ‘sea’ of electrons)

Conduct electricity – flow of electronsConduct electricity – flow of electrons

Malleable – hammered into sheetsMalleable – hammered into sheets

Ductile – draw into wireDuctile – draw into wire

Ionic Crystal StructureIonic Crystal Structure

Note: the smaller size of the cations relative to the anions. The packing of the ions determines crystal shape.

Covalent BondCovalent Bond

Interatomic forces are created by the Interatomic forces are created by the sharing of electronssharing of electrons..

The atoms share their s and p electrons to The atoms share their s and p electrons to attain the electron configuration of a noble attain the electron configuration of a noble gasgas

Atoms have small differences in Atoms have small differences in electronegativityelectronegativity

Generally low melting points (many are Generally low melting points (many are liquids and gases at room temperature)liquids and gases at room temperature)

The Octet RuleThe Octet Rule

Atoms react by gaining or losing electrons Atoms react by gaining or losing electrons so as to acquire the stable electron so as to acquire the stable electron configuration of a noble gas. Usually eight configuration of a noble gas. Usually eight valence electronsvalence electrons

Lewis Dot StructuresLewis Dot Structures

Bond FormationBond Formation

A bond forms when two electron clouds A bond forms when two electron clouds overlap and occupy a common orbital overlap and occupy a common orbital (molecular orbital)(molecular orbital)

Overlap of ‘s’ and ‘p’ orbitalsOverlap of ‘s’ and ‘p’ orbitals

s, s overlap

s, p overlap

p, p overlap

Sigma Bonds Pi Bonds

p, p side by side overlap

Nonpolar Covalent BondsNonpolar Covalent Bonds

When the electrons are equally shared the bond When the electrons are equally shared the bond between the atoms is nonpolar. Note the even between the atoms is nonpolar. Note the even distribution of the electron cloud of the hydrogen distribution of the electron cloud of the hydrogen moleculemolecule

Polar Covalent BondsPolar Covalent Bonds

Polar – an unsymmetrical distribution of Polar – an unsymmetrical distribution of electric charge due to the unequal sharing electric charge due to the unequal sharing of electonsof electons

The electronegativity difference between The electronegativity difference between the atoms determines the degree of the atoms determines the degree of polaritypolarity

What Type of Bond Is It?What Type of Bond Is It?

Electronegativity Electronegativity DifferenceDifference

Most Probably Most Probably Type of BondType of Bond

ExampleExample

0.0 – 0.40.0 – 0.4 Nonpolar CovalentNonpolar Covalent H-HH-H

0.4-1.00.4-1.0

Moderately Polar Moderately Polar CovalentCovalent H-ClH-Cl

1.0-2.01.0-2.0

Very Polar Very Polar CovalentCovalent H-FH-F

>> 2.0 2.0 IonicIonic NaClNaCl

Classifying CompoundClassifying Compound

Molecular – held together with Molecular – held together with covalent bondscovalent bonds

Network Solid (Ionic) – held together Network Solid (Ionic) – held together with ionic bondswith ionic bonds

Dipole MomentDipole Moment

The measure of the force exerted on a The measure of the force exerted on a dipole ( a single bond)dipole ( a single bond)

DipoleDipole

A molecule that has an uneven distribution A molecule that has an uneven distribution of charge even though the molecule as a of charge even though the molecule as a whole is electrically neutralwhole is electrically neutral

The Water MoleculeThe Water MoleculeA Polar MoleculeA Polar Molecule

There are two polar covalent bonds and the bent shape of the molecule causes the uneven distribution of charge resulting in a polar molecule.

The Methane MoleculeThe Methane Molecule

The even distribution of the charge results in a nonpolar molecule

Non-polar MoleculesNon-polar Molecules

The individual C-O bonds are polar in nature but the The individual C-O bonds are polar in nature but the overall molecule is nonpolar due to the even or balanced overall molecule is nonpolar due to the even or balanced distribution of charge.distribution of charge.

Another ExampleAnother Example

The CFThe CF44 molecule has 4 evenly distributed polar molecule has 4 evenly distributed polar

bonds resulting in no net dipole for the molecule. bonds resulting in no net dipole for the molecule. The result is a nonpolar molecule The result is a nonpolar molecule

Coordinate Covalent BondCoordinate Covalent Bond

Also known as a “Dative Bond”Also known as a “Dative Bond” A covalent bond in which both electrons A covalent bond in which both electrons

are donated by a single atomare donated by a single atom

Expressions of Chemical FormulasExpressions of Chemical Formulas

Chemical formula HChemical formula H22

Lewis Dot structure (dots represent Lewis Dot structure (dots represent valence electrons) H:Hvalence electrons) H:H

Dash formula H-H (dash represents a pair Dash formula H-H (dash represents a pair of electrons –a bond)of electrons –a bond)

Electron Dot FormulasElectron Dot Formulas

Let Us Practice Some Lewis Dot Let Us Practice Some Lewis Dot Structures!Structures!

Water HWater H22OO

Methane CHMethane CH44

Ammonia NHAmmonia NH33

Carbon Tetrachloride CClCarbon Tetrachloride CCl44

Let’s see how we did!Let’s see how we did!

WaterMethane

Ammonia Carbon Tetrachloride

Some Common Molecular ShapesSome Common Molecular Shapes

LinearLinear

BentBent

PyramidalPyramidal

TetrahedralTetrahedral

Bonding and Molecular OrbitalsBonding and Molecular Orbitals

Sigma BondsSigma Bonds Single bondsSingle bonds

• Overlap of two s orbitals Overlap of two s orbitals • Overlap of an s and a p orbitalOverlap of an s and a p orbital

Pi BondsPi Bonds Double or Triple bondsDouble or Triple bonds

• Side by side interaction of two p orbitalsSide by side interaction of two p orbitals

Sigma Bonds (Sigma Bonds (

When two atomic orbitals combine to When two atomic orbitals combine to form a molecular orbital along the form a molecular orbital along the internuclear axisinternuclear axis

When two carbon atoms bond there is an overlap of atomic orbitalsalong the internuclear axis.

When carbon bonds with the hydrogens there is an overlap of hydrogen’s ‘s’ orbitals with carbons atomic orbitals to produce 6 sigma bonds.

Ethane C2H6

Pi Bonds (Pi Bonds (

When two atomic orbitals combine to form When two atomic orbitals combine to form a molecular orbital above and below the a molecular orbital above and below the internuclear axisinternuclear axis

Can result from the side by side interaction Can result from the side by side interaction between two ‘p’ orbitals between two ‘p’ orbitals

The Carbon Carbon Double BondC=C

Consists on one and one bond

So why does carbon bond with 4 So why does carbon bond with 4 equal energy orbitals?equal energy orbitals?Why does carbon form Why does carbon form tetrahedral geometry?tetrahedral geometry?

Answer:Answer:

Hybrid Orbital TheoryHybrid Orbital Theory

Carbons 1-s and 3-p valence orbitals combine to result in 4 equal energy bonding orbitals

The four equal energy orbitals account for carbons tetrahedral geometry

spsp22 Hybridization in Boron Hybridization in Boron

Results in trigonal planar geometry

sp Hybridization in sp Hybridization in BerylliumBeryllium

Explains linear geometryExplains linear geometry

Molecular Shapes Molecular Shapes

LinearLinear

BentBent

PyramidalPyramidal

Trigonal PlanarTrigonal Planar

TetrahedralTetrahedral

Energy Changes in Bond FormationEnergy Changes in Bond FormationBonding and Antibonding OrbitalsBonding and Antibonding Orbitals

* Notice that the molecular orbital is lower

energy then the atomic orbitals

The energy levels in a hydrogen molecule can be represented in a diagram - showing how the two 1s atomic orbitals combine to form two molecular orbitals, one bonding () and one antibonding (*)