For example, the atomic number of lithium is 3. Every lithium atom has 3 protons and 3 electrons. It has 3 positive charges and 3 negative charges.
Atoms of different elements usually have different mass numbers, but they can be the same. For example, the mass number of argon atoms and calcium atoms can both be 40.
The symbol for an atom can be written to show its mass number and its atomic number.
To calculate the numbers of subatomic particles in an atom use its atomic number and mass number:
The atomic number of a fluorine atom is 9 and its mass number is 19. Calculate the number of protons, neutrons and electrons it contains.
number of protons = 9
number of electrons = 9
number of neutrons = mass number - atomic number
= 19 - 9 = 10