Essential Concepts: Molecular (Covalent) Compounds

Obj 1 Contrast the properties of ionic compounds with molecular compounds

Ionic Compounds / Molecular Compounds
Bonds / Ionic (attraction of oppositely charged ions, that result from the transfer of electrons to achieve noble gas stability) / Covalent (results from the sharing of electrons to achieve noble gas stability)
Components / Metal with nonmetal or polyatomic ions (those made of several atoms) / Nonmetals only
Solubility / Highly soluble in water / Some soluble, many not
Melting point / High (tend to be solid crystals) / Relatively low (many are liquid or gas at room temperature)
Conductivity / Strong conductors of electricity / Do not conduct electricity

Obj 2 name a binary molecular compound when given the formula of a compound

Molecular compounds are usually composed of two or more nonmetals which share electrons to form what are called covalent bonds, which are very strong. Ions are not formed. Many molecular compounds exist as gases or liquids at room temperature. Water and carbon dioxide are common examples. Unlike ionic compounds, molecules are made of exact numbers of atoms. For example a molecule of water is made of two hydrogen atoms and one oxygen atom. Some molecules are soluble in water (sugar) but many are not (oil). Because ions are not present, molecular solutions do not conduct electricity even when dissolved or melted.

Chemical formulas of molecular compounds. Molecular compounds are represented in chemical formulas as molecular formulas which show the number and kinds of atoms present in a molecule. A hydrogen peroxide molecule is made of 2 hydrogen atoms and 2 oxygen atoms. It's molecular formula is H2O2. (Note: molecular formulas represent the actual number of atoms in a particle and are not reduced to the lowest ratio, as are ionic formula units.) Glucose, another molecule, has the formula C6H12O6.

Naming molecular compounds. The following prefixes are used to indicate the number of atoms of each type in a molecular compound: mono- (for 1), di- (for 2), tri- (for 3), tetra- (for 4), penta- (for 5), hexa- (for 6), hepta- (for 7), octa- (for 8), nona- (for 9) and deca- (for 10). The atoms are listed in the order they occur in the molecular formula. Note:

·  change the ending of the last element of binary molecular compounds to –ide (like you do for binary ionic compounds);

·  if the first element listed is represented by only one atom then do not use a prefix (example CO2 = carbon dioxide, not monocarbon dioxide);

·  if the element begins with a vowel, the vowel at the end of the prefix is often dropped (monoxide, not mono-oxide).