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2/13/2011 Molecular Elements • A MOLECULE is a combination of two or more atoms held together by covalent bonds. • A COVALENT BOND is a connection, between two non-metals, in which the two atoms SHARE a pair of electrons. • Several non-metals exist as molecules • DIATOMIC MOLECULES are made up of 2 atoms Review Topic Five: Molecular Compounds Properties, Naming and Writing Chemical Formulas • Bohr diagram can illustrate the SHARING of electrons in a covalent bond between two chlorine atoms. Remember! Covalent bonds involving SHARING of electrons Elemental chlorine is a diatomic molecule (Cl2). Chlorine dissolves in water and is used to disinfect water in drinking supplies and swimming pools. Properties of Molecular Compounds • Molecular compounds are often soft • If they dissolve in water, they form solutions that do NOT conduct electricity • Tend to have relatively LOW melting points – Table sugar (sucrose) Naming Binary Molecular Compounds • Binary compounds consist of exactly TWO elements. • Naming binary molecular compounds that do NOT contain hydrogen atoms use GREEK prefixes to indicate how many atoms are present Writing Binary Molecular Compounds Naming Binary Molecular Compounds Steps 1. Name the first element. Example N2O nitrogen 2. Name the second element oxide using the suffix “-ide”. 3. Add prefixes to indicate the number of each atom. dinitrogen monoxide Example PBr3 phosphorus bromide phosphorus tribromide Steps Example disulphur decafluoride Example carbon tetrachloride • The prefix “mono-” is NOT used when the first element is only one atom. 1. Identify the first element, and give its symbol. S C • When the prefix “mono-” is required for before “oxide”, the last “o” in the prefix is dropped, it is “monoxide” NOT “monooxide”. 2. Identify the second element, and give its symbol. 3. Add subscripts to indicate the numbers of atoms. F Cl “di” 2 “deca” 10 “tetra” 4 S2F10 CCl4 Using “mono-” Properly 4. Write the formula 1