posted by Ernest .
Predict the empirical formula of the compound formed by each of the following pairs of elements.a) Li,S b) Na,H c) Al,l d) Ca,O
Look at the periodic table.
Li is in I so it has a valence of +1. S is in group VI (or 16 depending upon the system you are using) and it has a valence of -2; therefore, the formula is Li2S (Note that Li at +1 each is +2 total and that is neutralized by the -2 for S). Compounds must be zero.
Na is in group I BUT it is also in group VII on my chart( meaning it can have a valence of +1, which is the most usual, but it also can have -1 so the formula is NaH. Now you try the others.