Why do you think the Na+ ion is smaller than a neutral Na atom?

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom. 

Atp, shorthand for adenosine triphosphate, is the standard molecule for cellular enger in the human body. all motion and metabolic  processes  within the body begins with energy that is released from  atp, as its phosphate bonds are broken in cells through a  process  called hydrolysis.