Naming Covalent (Molecular) Compounds

Properties of Covalently Bonded Compounds Usually TWO NONMETALS bonded together Two nonmetals share electrons between them Can be Gases, Liquids or “squishy” solids. Generally have LOW melting and boiling points Do not conduct electricity well Usually not very soluble in water

How are covalent compounds different than Ionic ones? Metal – Nonmetal bond Electrons are transferred Generally solid High Melting/Boiling pts Conduct electricity when melted or dissolved Nonmetal-Nonmetal bond Electrons are shared Solid, Liquid or gas Low Melting/Boiling pts Do not conduct

What is the basic structural unit of a covalent compound? Covalent compounds form MOLECULES Bonding between atoms in a molecule is generally much, much stronger than the attraction between different molecules. Married couples analogy…

How are covalent compounds different than Ionic ones? Basic Structural unit is the “Unit cell” or the “formula unit” Ions arranged in crystal structure Basic structural unit is the MOLECULE Molecules may attract each other but that attraction is small compared with internal bonding

Naming molecules from their formulas CO2 N2O B2H6 CH4 NH3 Use the Prefixes… 1 – mono 2 – Di 3 – Tri 4 – Tetr(a) 5 – Pent(a) 6 – Hex(a) 7 – Hept(a) 8 – Oct(a) 9 – Non(a) 10 – Dec(a)

Naming molecules from their formulas CO2 carbon dioxide N2O dinitrogen monoxide B2H6 diboron hexahydride CH4 carbon tetrahydride commonly known as “Methane” NH3 nitrogen trihydride commonly known as “Ammonia” Use the Prefixes… 1 – mono 2 – Di 3 – Tri 4 – Tetr(a) 5 – Pent(a) 6 – Hex(a) 7 – Hept(a) 8 – Oct(a) 9 – Non(a) 10 – Dec(a)

Writing formulas for molecules from their names Carbon monoxide Sulfur trioxide Silicon tetrachloride Diphosphorus pentachloride Tetraphosphorus triselenide Writing formulas for molecules from their names Use the Prefixes… 1 – mono 2 – Di 3 – Tri 4 – Tetr(a) 5 – Pent(a) 6 – Hex(a) 7 – Hept(a) 8 – Oct(a) 9 – Non(a) 10 – Dec(a)

Writing formulas for molecules from their names Carbon monoxide CO Sulfur trioxide SO3 Silicon tetrachloride SiCl4 Diphosphorus pentachloride P2Cl5 Tetraphosphorus triselenide P4Se3 Use the Prefixes… 1 – mono 2 – Di 3 – Tri 4 – Tetr(a) 5 – Pent(a) 6 – Hex(a) 7 – Hept(a) 8 – Oct(a) 9 – Non(a) 10 – Dec(a)

Practice naming and writing formulas WARNING! Some of the compounds listed below are NOT covalent. Make sure you don’t use prefixes when naming them. Name these compounds: CBr4 , N2O5, MgF2 , SeS , Write formulas for these: Carbon disulfide, Disilicon hexahydride, Potassium carbonate, Dinitrogen tetroxide Practice naming and writing formulas Use the Prefixes… 1 – mono 2 – Di 3 – Tri 4 – Tetr(a) 5 – Pent(a) 6 – Hex(a) 7 – Hept(a) 8 – Oct(a) 9 – Non(a) 10 – Dec(a)