TWO REALLY IMPORTANT NUMBERS TO KNOW ARE CALLED.. 

The ATOMIC NUMBER 

and 

The ATOMIC MASS 

The Atomic Number

The atomic number is the number of PROTONS that each atom has in its nucleus. 

The atomic number is also the POSITION of that element in the periodic table (1,2,3...118) 

It is also the number of electrons that the neutral atom has.

The elements are arranged by increasing atomic number from Hydrogen (1) to Uranium (92) and beyond. It is the smaller number found in the element info box and it is always a whole number.

The Atomic Mass (also know as mass number)

The atomic mass is the average number of PROTONS and NEUTRONS

that each element has in its nucleus. This is the larger number and it

almost always is a 'decimal number'.