When determining the formula for a compound it is important to know the valence numbers of each element. Suppose you want to-write a formula for a compound with these two elements?

Answer 1

To be stable it would need to be A2B (2 of element A would give a total of 6 valence electrons + the 1 element B would give a total of 8 electrons in the covalent bond. The bond is now stable and you have a compound.)

Answer 2

Valence numbers are used to determine the formula when the compound is ionic, such as in NaCl, HCl, CaCl2. The metal (or Hydrogen) has a positive charge: Na and H have +1 valence (they give up 1 electron), and Ca has +2 valence (gives up 2 electrons). Chlorine has -1 valence (it takes on an extra electron).

Back to your question. You must balance the electrons in A and B (and one must be positive and the other negative or there won't be an ionic bond). To balance the electrons, find the Least Common Multiple of the two numbers: for 3 and 2 this is 6, so there will be 6 total electrons being transferred.

Since A is valence 3, you need 2 of A to get 6 electrons, and since B is valence 2, you need 3 of B: the formula would be A2B3

Answer 3

Presuming that Element B has valency of 2, then the resulting compound will most probably be 2 atoms of element A for every 3 atoms of element B.