Chapter 16Covalent Bonding

The Nature of Covalent Bonding

Bonding Theories

Polar Bonds and Molecules

Chapter 16.1 The Nature of Covalent Bonding

Single Covalent Bonds

Double and Triple Covalent Bonds

Coordinate Covalent Bonds

Bond Dissociation Energies

Resonance

Exceptions to the Octet Rule

Single Covalent Bonds

A bond in which two atoms share a pair of electrons (usually non-metals)

The pair of electrons is represented by a dash

Structural formulas – chemical formulas that show the arrangement of atoms in molecules or poly atomic ions

Single Covalent Bonds

Hydrogen

H2

H H

H-H

Single Covalent Bonds

Water

Ammonia

Methane

Double and Triple Covalent Bonds

Double Covalent Bonds – involve two shared pairs of electrons

Triple Covalent Bonds – involve three shared pairs of electrons

Double and Triple Covalent Bonds

Nitrogen

N2

N N

N N

Coordinate Covalent Bond

One atom contributes both bonding electrons

Carbon Monoxide

Bond Dissociation Energies

The total energy required to break the bond between two covalently bonded atoms

H-H + 435kJ = H + H

C-C + 347kJ = C + C

Bond Dissociation Energies

Bond Bond Energy Bond Length

H-H 435 74

C-H 393 109

C-O 356 143

C=C 657 133

Resonance

Structures that have two or more different electron dot structures that have the same number of electron pairs for the same molecule or ionOzone

NO3-

http://www.nku.edu/~russellk/tutorial/reson/NO3.gifhttp://www.nku.edu/~russellk/tutorial/reson/CO3.gif

Exceptions to the Octet Rule

Occurs when the total number of valence electrons is an odd number.

NO2 (Two resonance structures)

BF3

PCl3 and PCl5SF6

Diamagnetic

All electrons pairedThe spinning of electrons creates magnetic fields. The paired electrons spin in opposite directions, therefore their fields cancel each other outShow a weak attraction to an external magnetic field

Paramagnetic

Contain one or more unpaired electrons

Creates a magnetic field

Show a strong attraction to an external magnetic field

Oxygen – An Exception

O=O

Actually a mix ofO=O and O-O

Ch 16.2 Bonding Theories

Molecular Orbitals

VSEPR Theory

Hybrid Orbitals

Molecular Orbitals

An orbital resulting from the overlapping of orbitals from two atoms when they bondBonding orbital – molecular orbital with an energy lower than the atomic orbitalAntibonding orbital – molecular orbital with an energy higher than the atomic orbital

Molecular Orbitals

Sigma Bond – a molecular orbital that is symmetrical along the axis connecting two atomic nuclei

Two s orbitals directly overlap

Molecular Orbitals

Pi bonds - two parallel 'p' orbitals in close proximity can overlap sideways (laterally)

A pi bond can only form after a sigma bond has already formed

VSEPR Theory

Electron pairs repel, so molecules adjust shape to keep the pairs as far apart as possible

Unbonded electrons repel bonded electrons more, causing the bonded electrons to be closer together

http://www.mikeblaber.org/oldwine/chm1045/notes/Geometry/VSEPR/Geom02.htm

Ch 16.3 Polar Bonds and Molecules

Bond Polarity

Polar Molecules

Attractions Between Molecules

Intermolecular Attractions and Molecular Properties

Bond Polarity

Nonpolar Covalent Bond – equal sharing of electrons, each atom pulls equally (same atoms)

Polar Covalent Bond – unequal sharing of electrons (different atoms)

Bond Polarity

The more electronegative atom will have a greater pull and acquire a slightly negative charge.

HCl

H2O

Bond PolarityElectronegativity

DifferenceType of Bond Example

0.0 – 0.4 Nonpolar Covalent H-H

0.4 – 1.0 Moderately Polar Covalent

H-Br

1.0 – 2.0 Very Polar Covalent

H-F

>2.0 Ionic NaCl

Polar Molecules

Dipole – a molecule with two poles (different charges)

Polarity depends on shape

Atoms that lie in the same axis will cancel each other out

Attractions Between Molecules

van der Waals forces – weak attractions between molecules – Two TypesDispersion Forces – Weak attraction due to

movement of molecules, increase with more electrons (diatomic halogens)

Dipole Interactions – polar molecules attracted to each other (water molecules)