All of those letters and numbers probably look a little bit scary, so let’s break it down and look at just one element.
The number at the top (from 1-116) is the atomic number. The atomic number tells where an element is located on the periodic table as well as the number of protons and electrons the atom has.
Atomic number = number of protons and number of electrons
The one or two letters in the middle of the box is the element’s symbol. These are used to identify the element.
The number at the bottom is the atomic mass. The atomic mass is the average of the masses of naturally occuring atoms of that element. The atomic mass helps you to identify the number of neutrons in an atom.
Number of neutrons = atomic mass rounded to the nearest whole number – the atomic number.