Molecules and Molecular Compounds
A molecule consists of two or more atoms bound together.
Each molecule has a chemical formula.
The chemical formula indicates
1. Which atoms are found in the molecule, and
2. In what proportion they are found.
A molecule made up of two atoms is called a diatomic molecule.
Different forms of an element which have different chemical formulas are
known as allotropes. Allotropes differ in their chemical and physical
properties.
Compounds composed of molecules are molecular compounds.
• These contain at least two types of atoms.
• Most molecular substances contain only nonmetals.
Molecular formulas
Give the actual numbers and types of atoms in a molecule.
Table 5-5a - Some Molecular Formulas and the Information they Convey
Formula
H2O
O2
CO2
Composition
Total of 3 atoms in each molecule - 1 oxygen and 2 hydrogen
Total of 2 atoms in each molecule - 2 oxygen atoms
Total of 3 atoms in each molecule - 1 carbon and 2 oxygen
C6H12O6 Total of 24 atoms in each molecule - 6 carbon, 12 hydrogen, and 6 oxygen.
While the molecular formula shows the molecule as it actually exists, the
Empirical formula for a compound shows the simplest whole number
ratio for the elements in the compounds. .
Table 5-5b - Comparing Empirical and Molecular Formulas
Compound
Water
Molecular Formula
Empirical Formula
H2O
H2O
Hydrogen Peroxide
H2O2
HO
Glucose
C6H12O6
CH2O
Methane
CH4
CH4
Ethane
C2H6
CH3
Octane
C8H18
C4H9