1. Chapter 6 section 2
Covalent bonding
Molecular compounds

2. A molecule is a neutral group of atoms that are held together by a covalent bond
A molecular compound is a chemical compound whose simplest units are molecules
A molecular formula show the types and numbers of atoms combined in a single molecule of a molecular compound.
A chemical formula indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts.

3. Two H atoms bond with one O atom to form H2O
if we look at the difference in electronegativity, we see that H is 2.1 and O is – 2.1 = 1.4 so the bond between H and O is a polar covalent bond.
By definition a neutral group of atoms held together by covalent bonds is a molecule.
So, the H2O particle is a molecule
H2O is a molecule which makes H2O a molecular compound and a molecular formula.
But H2O is also a chemical formula because we use atomic symbols and subscripts to describe it.

4. Diatomic molecule
A diatomic molecule is a molecule containing only two atoms of the same element.
There are seven elements that exist as diatomic molecules in nature
Ex: H2 N2 O2 F2 Cl2 I2 Br2

5. Formation of a covalent bond

6. Bond energy is the energy required to break a chemical bond and form neutral isolated atoms.

7. Octet rule
Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet (8) of electrons in it’s highest energy level.

8. Electron dot notation
On board

9. Lewis Structure
On board

10. Multiple covalent bonds
On board

11. Resonance Structures

12. Resonance Structures
Resonance structures refers to bonding in molecules or ions that cannot be correctly represented by a single Lewis structure

13. Resonance Structures
For example: NH3 – ammonia has only one correct structure .. N
H H H

14. Resonance Structures
But some structures have more than one Lewis Structure;
O3 - Ozone
O O O or O O O

15. Resonance Structures