NAMING #5 Naming Molecular Compounds

WHICH COMES FIRST? The more positive of the 2 elements comes first. The more positive element is the one that is further to the left and down on the periodic table. (i.e., the less ______________________ one comes first

NAMING THE ELEMENTS The more positive element is called by its name. The more negative element is called by part of its name and the ending ide. These are the same names as the anions of the elements have. e.g. oxide, sulfide, fluoride, chloride, bromide, iodide, nitride, hydride, selenide

If you are asked to write the name for this ionic compound- Al 2 S 3 - you just say ___________________________________ You do not need to say di or tri, because aluminum in a compound is always _____, and sulfur in an ionic compound is always ______, so they must exist in a __________ ratio.

However, in molecular compounds, the elements mostly don’t form ________________ charges, because the electrons are_______________, not lost or gained.

Example: What is the formula for phosphorous chloride? The answer is: __________________________________ There are 2 different compounds formed from phosphorous and chlorine. They are

PREFIXES MUST BE USED You can not tell how many atoms of each element there is in a molecular compound (as you can by using the charges in ionic compounds). Therefore, you must put prefixes in the name to designate how many atoms of each element there is. PCl 3 = phosphorous trichloride PCl 5 = phosphorous pentachloride PREFIXES YOU MUST KNOW mono one pentafive di two hexasix tri three heptaseven tetra four

IMPORTANT RULE: The first element only has a prefix if there are more than one of those atoms. The second element always has a prefix.

EXAMPLES – formulas to names SF 6 CO 2 N 2 O 4

EXAMPLES – Name to formulas sulfur trioxide nitrogen trihydride diphosphorous pentasulfide

PRACTICE – Fill in the blanks CCl 4 ____________________________ Se 3 F 7 ____________________________ SiS 2 ____________________________ ______________ carbon dioxide ______________ silicon tetrabromide _______________ trinitrogen hexachloride