Covalent BondingCovalent Bonding

Chapter 6Chapter 6

Section 1Section 1

Covalent BondsCovalent Bonds

Ionic bond – transfer of e-Ionic bond – transfer of e-Covalent bondCovalent bond – a bond formed – a bond formed

when atoms share one or more when atoms share one or more pairs of electronspairs of electrons

Example – HExample – H22

H is diatomic – come in 2’sH is diatomic – come in 2’sThe + nucleus of each atom The + nucleus of each atom

attracts the e- of both atoms attracts the e- of both atoms The + nucleus of each atom The + nucleus of each atom

repels each otherrepels each otherThe – e- cloud of each atom The – e- cloud of each atom

repels each otherrepels each other

Hydrogen’s Molecular OrbitalHydrogen’s Molecular Orbital

Single BondSingle Bond

2 atoms share 1 pair of e- 2 atoms share 1 pair of e- Represented by a single line HRepresented by a single line H

—H is H—H is H22

The e- cloud is around both H The e- cloud is around both H nuclei called a molecular orbitalnuclei called a molecular orbital

Molecular OrbitalMolecular Orbital

Molecular orbitalMolecular orbital – region where – region where e- pair is most likely to exist e- pair is most likely to exist around 2 nucleiaround 2 nuclei

Results from overlap of two Results from overlap of two atomic orbitals.atomic orbitals.

Potential EnergyPotential EnergyBonds will form when they can be the Bonds will form when they can be the

most stable = low Emost stable = low EMost atoms have low stability and Most atoms have low stability and

high potential E until they bond with high potential E until they bond with other atomsother atoms

At 75 pm, the repulsion b/t like At 75 pm, the repulsion b/t like charges = the attraction b/t opposite charges = the attraction b/t opposite charges.charges.

E here is -436kJ/molE here is -436kJ/mol

Potential EnergyPotential Energy

Bond Length Bond Length

Bond lengthBond length – the distance b/t 2 – the distance b/t 2 bonded atoms at min. pot. E; the bonded atoms at min. pot. E; the avg. distance b/t the nuclei of 2 avg. distance b/t the nuclei of 2 bonded atomsbonded atoms

HH22 = 75 pm = 75 pmAtoms vibrate in bonds and act Atoms vibrate in bonds and act

like a spring so length always like a spring so length always changeschanges

Bond EnergyBond EnergyBond energyBond energy – the E required to – the E required to

break a chemical bond b/t 2 atomsbreak a chemical bond b/t 2 atomsHigher the E the stronger the Higher the E the stronger the

bond and smaller the bond bond and smaller the bond lengthlength

HH22 is - 436 kJ/mol – E released is - 436 kJ/mol – E released when 1 mol of Hydrogen bonds when 1 mol of Hydrogen bonds is 436 kJ/molis 436 kJ/mol

ElectronegativityElectronegativity

ElectronegativityElectronegativity - the tendency of - the tendency of an atom to attract bonding e-’s to an atom to attract bonding e-’s to itself when it bonds w/ another atomitself when it bonds w/ another atom

Trend: electronegativity increases Trend: electronegativity increases going left to right and decreases going left to right and decreases down a groupdown a group

Fluorine is the most e-neg. element.Fluorine is the most e-neg. element.

Electronegativity and BondingElectronegativity and Bonding

Helps to determine if the bond will Helps to determine if the bond will be ionic or covalentbe ionic or covalent

Greatly different = ionic bondGreatly different = ionic bondClose = covalent bondClose = covalent bond

Types of Covalent BondsTypes of Covalent Bonds

Nonpolar covalent bondNonpolar covalent bond – covalent – covalent bond where the bonding e- are = bond where the bonding e- are = attracted to both bonded atoms attracted to both bonded atoms

Polar covalent bondPolar covalent bond – covalent – covalent bond where a shared pair of e- is held bond where a shared pair of e- is held more closely by 1 of the atomsmore closely by 1 of the atoms

Polar Covalent BondPolar Covalent Bond

The more e-neg atom has a The more e-neg atom has a higher e- density b/c it has a higher e- density b/c it has a greater attraction for e-’sgreater attraction for e-’s

Predicting Bond CharacterPredicting Bond Character

Diff. in e-negDiff. in e-neg Bond TypeBond Type

0-0.50-0.5 non polar non polar covalentcovalent

0.5-2.10.5-2.1 polar covalentpolar covalent

>2.1>2.1 ionicionic

Predicting Bond CharacterPredicting Bond Character

Consider Al FConsider Al F33 - The e-neg diff b/t - The e-neg diff b/t

Al and FAl and F33 is 2.4 It is an ionic bond is 2.4 It is an ionic bondThe e-neg diff b/t Al and C is 1.6 The e-neg diff b/t Al and C is 1.6

It is a polar covalent bond.It is a polar covalent bond.

PolarityPolarity

Polarity – having opposite ends, Polarity – having opposite ends, or polesor poles

DipoleDipole – a molecule in which one – a molecule in which one end has a partial positive charge end has a partial positive charge and the other has a partial and the other has a partial negative chargenegative charge

HFHF

HF is a polar molecule HF is a polar molecule Use Greek lowercase letter delta Use Greek lowercase letter delta

– – δδ++ partial positive partial positive δδ-- partial partial negativenegative

H H δδ++ F F δδ--

PolarityPolarity

It is possible to have polar ends It is possible to have polar ends but for the molecule not to be a but for the molecule not to be a dipoledipole

This happens when the polar This happens when the polar sides cancel each other outsides cancel each other out

Dipole MomentDipole Moment

Dipole Moment – measures the Dipole Moment – measures the polarity of a moleculepolarity of a molecule

The larger the dipole moment, the The larger the dipole moment, the greater the polarity = the stronger greater the polarity = the stronger the bondthe bond

H-F = 1.8 Dipole MomentH-F = 1.8 Dipole MomentH-I = 0.5 Dipole MomentH-I = 0.5 Dipole Moment

AssignmentAssignment

Complete the section review on Complete the section review on page 198.page 198.

Turn in this assignment today Turn in this assignment today before you leave class.before you leave class.