Question

Why does chromium have a 3 charge? why is chromium (vi) oxide [cro3} not chromium 3 oxide?

Answer 1

Chromium (VI) has a 6+ charge (we can tell that from the number 6 after it) and you should know that Oxygen has a 2- charge (because it needs 2 more electrons to get a full outer shell).

To work out the formula we need to balance the positive and negative charges.

So we have 6+ and 2-...
We need to make 6- so therefore we times the amount of Oxygen by 3.

This makes the formula CrO3.

Hope this is helpful, message me if you have any questions :)