Chemistry Essay

2108 Words Jun 23rd, 2015 9 Pages
Centre for Foundation Studies, UTAR

CHAPTER 2
Chemical Bonding

Chapter Scopes
Bond energies, bond lengths & bond polarities Drawing Lewis structure and calculate the formal charge

Forms of Chemical Bonds
1) Intramolecular bond – forces hold the atoms _______ a molecule
• Ionic / Electrovalent Bond
• Covalent Bond
• Metallic Bond
2) Intermolecular bond – forces ________ the molecules • Hydrogen bonding
• Van der Waals
3) Co-ordinate / Dative Bond

FHSC1114 Physical Chemistry

Chapter Scopes





Electrovalent / ionic bonding
Covalent bonding
Co-ordinate / dative covalent bonding
Intermolecular bonding (including hydrogen bonding, Van der Waals)
• Metallic bonding
• Electronegativity

Chemical
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Therefore, N is central.
2) Count valence electrons
H = 1, N = 5
Total = (3 x 1) + 5 = 8 electrons / 4 pairs

3) Form a single bond between the central atom and each surrounding atom

Example 2: Carbon Dioxide, CO2
1) Central atom = _______
2) Valence electrons = __ e- or __ pairs e3) Form bonds
O C O 6 pairs of electrons are now left

4) Remaining electrons form LONE PAIRS to complete octet (8 e-) as needed
••

4) Place lone pairs on outer atoms

3 BOND PAIRS and 1 LONE PAIR

FHSC1114 Physical Chemistry

2

Centre for Foundation Studies, UTAR

Example 3: Sulfur Dioxide, SO2
1) Central atom = _____
2) Valence electrons = __ e- or ___ pairs e3) Form bonds
Leave 14 e4) Remaining pairs become lone pairs, first on outside atoms and then on central atom ••
••
••

5) So that C has an octet, we shall form
DOUBLE BONDS between C & O

Each atom is surrounded by an octet of electrons

5) Form double bond so that has an octet — but note that there are 2 ways of doing this bring in left pair
••

O
••

••

S

••

O
••

••

••

or bring in right pair

S

O
••

••

••

O

••

Resonance Structures
• 2 or more Lewis structures can be drawn for a molecule or polyatomic ion
• For example:
a) Sulfur dioxide, SO2

This leads to the following structures
••

O
••

••

S

••

••

O
••

••

••

••

S

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