chemical formula and equations

Question 1

How to write the chemical formula of compounds?

Answer 1

we need to know the valency of the electrons
to make an elemnt stable you must make the number of valence electrons 8 (a full outermost shell) to obtain noble gas configuration. to do this you add or take away electrons. for example,
Na–> 2.8.1
make stable by -1 electron
Na instable form = +1 electron
Na valency = Na+

Question 2

After knowing the valency, how do you write a chemical formula?

Answer 2

1) Sodium Chloride
Na+ Cl-
1 1
cross multiply= NaCl
2) Sodium Sulfate
Na+ SO4-2
1 2
cross multiply= Na2SO4