Covalent Bonding

The joining of two or more elements through the sharing of valance electrons to form a molecule

Purpose: To form a stable octet between the elements

Types of Covalent Bonds

• Non-Polar: equal sharing of the valance electrons.

• Polar: unequal sharing of the valance electrons.

Non-Polar

• Shape of molecule is symmetrical.

• Homonuclear molecules.•Diatomic molecules:

•N2, O2, F2, Cl2, Br2, I2, and H2

•Makes the #7

Polar

• Shape of the molecules is asymmetrical due to unequal sharing of the electrons.

• Heteronuclear: one nuclear charge is stronger than another.

• Polarity is the function of the change in electronegativity (EN)• Increase EN, = more ionic chstc.

Polar Molecules

Rank these in decreasing covalent characteristics:

H2O, N2, NO3- , NaBr2, CO2

Solution:

1. Identify the electronegativity for each element in the molecule.

2. Less covalent > 1.7 > more covalent.

N2 > NO3- > CO2 > H2O > NaBr2

Lewis Dot Structure

• Pictorial representation of valance electrons.

• Dot structure• Stick structure

Octet Rule

• Representative elements share electrons to take on a Noble gas electron configuration.

• Each element in a molecule will follow the octet rule.

Shared Electrons

• Formula to determine the number of shared electrons:

• N – A = S• N = # of electrons needed to form

a Noble gas configuration.• A = # of electrons available in the

valance.• S = # of electrons shared

Bonding• Sigma Bonds are the single

electron overlap of the s orbital.• Forms single bonds, end-to-end.• Pi Bonds are the overlap of the s

and p orbitals.• Forms double and triple bonds w/ s

end-to-end and p side-to-side.

Practice Problems

• CO2

• N2

• CS2

• HNO3

• NO31-

• Which are polar?• Which are non-polar?• Which are non-polar with polar bonds?

Resonance

• Equally acceptable formulas.

• HNO3

• NO31-

Limits to the Octet Rule

• Most beryllium compounds• Most Group IIIA elements• Compound which require more

than 8e- in the valance.• Compounds containing d or f

transitional elements• ‘S’ with an odd number of

electrons

Practice Problems

• CCl4• CO2

• N2O5

• N2O

• S3O5

• NF3

Naming Molecules

• Follows the rules as ionic compounds except prefixes are used to note ‘how many’.

• Table 8-3, page 248.

Molecular Structure

• VB Theory : Valance Bond Theory, orbital overlaps

• VSEPR Theory: Valance Shell Electron Pair Repulsion Theory• Electrons arrange to max the distance

between electrons• Bonding pairs v. Unshared pairs

Molecular Geometry

• Linear (2) • Trigonal Planar• Tetrahedral• Trigonal Pyramidal• Angular (Bent)• Trigonal Bipyramidal• Octehedral

Linear

• Formula AB2 w/ no unshared pairs

• VSEPR: bonding angle of 180o

• VB: sp overlap• Forms a polar bond and a non-

polar molecule.

Trigonal Planar

• Formula of AB3 and no unshared pairs.

• VSEPR: bonding angle of 120o

• VB: SP2 overlap• Polar bond w/ non-polar molecule

Tetrahedral

• Formula of AB4 w/ no unshared pairs.

• VSEPR: bonding angle of 109.5o

• VB: sp3 overlap• Forms polar bonds and non-polar

molecule.

Trigonal Pyramidal

• Formula AB3 w/ one unshared pair on A.

• General: subtract 2.5o for each unshared pair.

• VSEPR: bonding angle of 107o

• VB: sp3 overlap w/ a polar bond and a polar molecule

Angular (Bent)

• Formula AB2 w/ 2 unshared pairs on A

• VSEPR: bonding angle of 104.5o

• VB: sp3 overlap w/ polar bonds and polar molecule.

Linear

• Formula AB w/ 3 unshared pairs• VSEPR: bonding angle of 102o• VB: sp3 overlap w/ polar bonds and

polar molecule.

Trigonal Bipyramidal

• Formula AB5 w/ no unshared pairs

• VSEPR: bonding angles at 90o, 120o and 180o

• VB: sp3d overlap w/ polar bonds and polar molecule.

Octahedral

• Formula AB6 w/ no unshared pairs

• VSEPR: bonding angles of 90o, 120o and 180o

• VB: sp3d2 overlap w/ polar bonds and molecule

Molecules

Molecule VB VSEPR Shape NI3PH3

CH4

SF6

H2S

PF5

BeCl2