How do you find the atomic number?

Calculate the number of neutrons. Now you know that atomic number = number of protons, and mass number = number of protons + number of neutrons. To find the number of neutrons in an element, subtract the atomic number from the mass number. read more

Find the atomic weight. The atomic weight is typically printed below the element name on the periodic table, usually to two or three decimal places. This is the average mass of one atom of the element, weighted to what you would expect to find in nature. This number is in "atomic mass units" (AMU). read more

If students do not have access to a periodic table, but know the number of protons and neutron of an element, they can still calculate the mass number. The equation for mass number is given as mass number = number of protons + number of neutrons. read more

All carbon atoms, and only carbon atoms, contain six protons and have an atomic number of 6. Oxygen atoms contain 8 protons and have an atomic number of 8. The atomic number of an element never changes, meaning that the number of protons in the nucleus of every atom in an element is always the same. read more