The answers would be:
Be₃N₂
Al₂S₃
Here's more about the question:
To find the chemical formula first you need to know the charges. You can do that by first figuring out the transfer of valence electrons of each so that it can complete the octet rule.
Let's start with Beryllium Nitride
Beryllium is a cation with a charge of 2+ and Nitrogen is an anion with a charge of 3-.
We write charges as superscripts:
Be³⁺ N²⁻
Now to get the formula, all you need to do is exchange superscripts but write them as subscripts.
Be₂N₃
Let's do the second one:
Aluminum sulfide
Another way I do this though, is just think of the first element and think about how many valence electrons it has, this is how many it can give away.
When you think about the second element, think about how many valence electrons it has, then think how many does it need to have 8.
Aluminum has 3 valence electrons (It can give away 3)
Sulfur has 6 valence electrons, (it needs 2 to complete 8)
Now those are your superscripts!
Al³⁺S²⁻
Then exchange!
Al₂S₃
