Question

Complete the chemical formula for each ionic compound. Consult the periodic table to help you answer the question. beryllium nitride: Be N. aluminum sulfide: Al S

Answer 1

Answer: Beryllium nitride: $Be_3N_2$

Aluminium sulphide: $Al_2S_3$

Explanation: For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.  

Here beryllium is having an oxidation state of +2 and nitrogen with oxidation state of -3. Thus they combine to form neutral $Be_3N_2$.

Similarly aluminium is having an oxidation state of +3 and sulphur with oxidation state of -2. Thus they combine to form neutral $Al_2S_3$.

Answer 2

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