What are the formula for the compounds?

What's CARBIDE? and Which Chemical Formula do we use for ionic compounds?

• I'm really confused about carbide, I think it's an ion and a subset of Carbon but I don't have any idea about its charge. For the second question, is it empirical formula? :) Thanks in advance!

• Answer:

  "Carbide" really isn't an ion since it does not exist in aqueous solution. There are two structures that can be called "carbide". The first is when carbon exists in the -4 oxidation state in combination with a metal. Aluminum carbide, Al4C3, is an example. But aluminum carbide is definitely NOT ionic. Aluminum carbide has a high melting point not because it has bonds which are "ionic" but because it forms a complex network of alternating aluminum and carbon atoms. Carbide, can also refer to the C2 radical with with an oxidation state of -2. Most metal carbides like sodium carbide, Na2C2 and calcium carbide, CaC2 take this form. The substances do not dissociate to form ions in aqueous solution. Instead carbides of this form (called acetylides) decompose in water to make acetylene. This was an important reaction in the 19th century and early 20th century because it provided the fuel for miners' "carbide lamps".