Bonding Part II

Unit 5 – BondingMrs. Callender

Lesson Essential Questions:

What are the characteristics of covalent bonds?

How are covalent bonds formed?

BondingForces that hold groups of atoms

together and make them function as a

unit.

BONDING

COVALENT Bonds Sharing of Electrons.

Covalent compounds tend to form so that each atom, by sharing electrons, has an octet of electrons in its highest occupied level.

These compounds involve nonmetals only.The term molecule is used exclusively for covalent bonding.

The OCTET Rule:The Diatomic Fluorine Molecule

Diatomic – Elements that only exist in pairs.

H2, O2, F2, Br2, I2, N2, Cl2. Remember HOFBrINCl

F1s 2s 2p

F1s 2s 2p

Each has seven valence

electrons.

F FTwo electrons between elements make one bond. It is represented with a line.

The OCTET Rule:The Diatomic Oxygen Molecule

Diatomic – Elements that only exist in pairs.

H2, O2, F2, Br2, I2, N2, Cl2. Remember HOFBrINCl

O1s 2s 2p

O1s 2s 2p

Each has six valence

electrons.

O OTwo pairs of electrons between elements makes a double bond.

The OCTET Rule:The Diatomic Nitrogen Molecule

Diatomic – Elements that only exist in pairs.

H2, O2, F2, Br2, I2, N2, Cl2. Remember HOFBrINCl

N1s 2s 2p

N1s 2s 2p

Each has five valence

electrons.

N NThree pairs of electrons between elements indicates a triple bond.

The HONC RuleHydrogens and Halogens form one covalent bond.Oxygen and Sulfur form two covalent bonds. One double bond or two single bonds.Nitrogen and phosphorus form three covalent bonds. One triple bond, one double and one single bond, or three single bonds.Carbon and Silicon form four covalent bonds. One triple bond and a single bond, two double bonds, four single bonds, or a double bond with two single bonds.

Completing a Lewis Dot Structure – CH3Cl

1. Evaluate the compound by looking at each elements

valence electron amounts.C 1s22s22p2 4 valence electrons.

H 1s1 1 valence electron x 3 for H3

Cl 1s22s22p63s23p5 7 valence electrons.

2. According to HONC – Carbon can bond to four other elements but hydrogen and chlorine will only bond once therefore Carbon will be the center of the molecule.

We know we have 14 total electrons to work with.

4 e- from C + 3(1) e- from H + 7 e- from Cl = 14 e-

Carbon will be centrally located in the molecule with the other elements surrounding it.

CHCl

HH

Each element to element needs a pair electrons for a bond.

Complete octets on elements except for hydrogen with remaining electrons. 14 – 8 = 6 electrons.

For each shared pair of electrons draw a line. Leave the unshared pair of electrons as dots.

Bond Length and Energy

BOND Length (pm) Energy (KJ/mole)

C-C 154 346

C=C 134 612

C=C 120 835

C-N 147 305

C=N 132 615

C=N 116 887

C-O 143 358

C=O 120 799

C=O 113 1072

N-N 145 180

N=N 125 418

N=N 110 942

RESONANCE

Occurs when more than one valid Lewis Dot Structure can be written for a particular molecule.

This is a resonance structure for ozone, O3. The actual structure is an average of both.

Draw the following compound: PBr3

5 e- from P + 3(7) e- from Br = 26 e-

Phosphorus will be centrally located in the molecule with the other elements surrounding it.

PBr BrBr

Each element to element needs a pair electrons for a bond.

Complete octets on elements with remaining electrons. 26 – 6 = 20 electrons.

For each shared pair of electrons draw a line. Leave the unshared pair of electrons as dots.

Draw the following compound: NH4+1

5 e- from N + 4(1) e- from H = 9 e- but since it is positive you must subtract another e- so the total is 8 e-.Nitrogen will be centrally located in the molecule with the other elements surrounding it.

N H HH

Each element to element needs a pair electrons for a bond. +1

Since this is an ion it needs placed in brackets with the charge in the upper right hand corner.

H