___Fe + ___O2 ___Fe2O3

4 Fe + 3 O2 -> 2Fe2O3

Explanation:

For the equation to be balanced with whole numbers, you need to double the amount of Fe2O3. This gives 6 oxygen molecules and 4 Fe molecules.

So the number of atoms will be Fe = 4 and O = 6.

For the visual Model Key, you will most likely have, 4 separate Fe molecules and 3 oxygen molecules (since oxygen exists as a diatomic - 2 oxygen molecules are attached to each other). For Fe2O3 you will have 2 molecules that go O-Fe-O-Fe-O.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.