Molecular Compounds

Recall: An ionic compound is when a metal atom donates its valence electron(s) to a non-metal atom. The oppositely charged ions are then attracted to one another and this attraction is called an ionic bond

A molecule is made up of two or more atoms. A diatomic molecule is made up of two atoms only (eg. H2, O2, N2, F2). A molecular compound is a type of pure substance when atoms of two or more different non-metals combine. Examples: Sugar (C6H12O6) Water (H2O) Aspirin (C9H8O4)

Molecular compounds are joined by a covalent bond A covalent bond is formed when atoms share electrons (not transferred, as seen in ionic bonds). Since the atoms share electrons, no ions are created and the atoms therefore have no charge.

Shared electrons Shared electrons

Properties of Molecular Compounds Soft Lower melting points (weaker than ionic bonds) Some are able to dissolve in water (eg. ammonia) and others cannot (eg. oil) Molecular compounds do NOT ionize (split into their ions) in water, therefore they are nonelectrolytes and do NOT conduct electricity Sugar MP: 186°C Salt MP: 801°C

Naming Molecular Compounds Name the 1st element Name the 2nd element using –ide Add prefixes to indicate the # of atoms in each element. If the 1st element has only 1 atom, omit ‘mono’ If the 2nd element has only 1 atom, use ‘mono’ but drop the last ‘o’ of the prefix (eg. monoxide) Drop the ‘a’ if 2nd element name starts with a vowel (eg. tetroxide) Examples: a) N2O5 b) CO c) S3Cl5 # Atoms Prefix 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca

Writing Formulas for Molecular Compounds Note: You can identify if it is a molecular compound if the elements are ALL non-metals. Ionic compounds have a metal AND a non-metal! Write the element symbols in order of appearance in its name. Add subscripts to indicate the # of atoms for each element (use prefixes to determine this). DO NOT reduce the formula! Examples: a) sulphur heptafluoride b) silicon tetroxide