Chapter 6 section 2 Covalent bonding Molecular compounds

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.

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 3.5. 3.5 – 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.

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

Formation of a covalent bond

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

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.

Electron dot notation On board

Lewis Structure On board

Multiple covalent bonds On board

Resonance Structures

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

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

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

Resonance Structures