Classify these elements by whether they get oxidized or reduced in the reactions shown here:
2Ca(s) + O2(g) = 2CaO (s)
F2(g) + 2Li(s) = 2LiF(s)
Calcium, Oxygen, Fluorine, Lithium. Is each one oxides or reduced?
You can think of oxidation as gaining an oxygen atom or losing two hydride ions (electrons!). Take the first equation, the calcium solid is gaining an oxygen, therefore becoming oxidized. Since you can’t have oxidation without reduction – they come as a package deal – this means that the oxygen is reduced.
The second equation can be done like this: the oxidation state of Li is (1+) since it’s an Alkali metal, which makes the F have a charge of (1-) in the compound LiF. You also need to know that any compound by itself has a charge of (0), so, splitting the reaction into halves:
F2 + 2e --> 2F(1-) and 2Li --> 2Li(1+) + 2e
You can see that the lithium is losing two electrons (oxidation!) and the fluorine is gaining two electrons (reduction!)
Hope that helps!