What does the atomic number of an atom tell you ?

Hello there!

The atomic number of an atom tells you an element's identity, and informs you of how many protons are present in the nucleus of the atom. 

For example;
Potassium is an element with the symbol "K" on the periodic table that belongs in the Alkali Metal group, and has an atomic number of 19. This means that Potassium has 19 protons. 

I hope this helps!

Where are the following questions

False, as a substance changes from a solid to a liquid and from a liquid to a gas the molecules get farther apart from each other