If an atom has 12 protons (atomic number = 12), it must be magnesium. So if an atom has 8 protons (atomic number = 8), it must be oxygen. The atomic number is tied to the position of the element in the Periodic Table, and so the number of protons defines what sort of element you are talking about. If there are 9 protons, there must be 10 neutrons for the total to add up to 19. The mass number counts protons + neutrons (19). The atomic number counts the number of protons (9). How many protons and neutrons has this atom got? Using fluorine as an example, this information can be given simply in the form: ![]() The mass number is also called the nucleon number - again you probably won't meet that at this level. No of protons + no of neutrons = MASS NUMBER of the atom The atomic number is also given the more descriptive name of proton number, and is related to the position of the element in the Periodic Table. No of protons = ATOMIC NUMBER of the atom Working out the numbers of protons and neutrons Virtually all the mass of the atom is concentrated in the nucleus, because the electrons weigh so little. You aren't very likely to meet this term at this introductory level. Protons and neutrons are collectively known as nucleons. The nucleus is at the centre of the atom and contains the protons and neutrons. Neutrons are neutral - they have no charge. The mass due to the electrons is negligibly small by comparison.Ī proton carries a positive charge an electron carries an equal negative charge. ![]() Most of the mass of an atom is due to the protons and neutrons. The table summarises the key facts about these particles. It finishes by looking at the existence of isotopes of elements. This page looks briefly at the three subatomic particles we talk about at this level (protons, neutrons and electrons), and then goes on to look at how you work out the numbers of protons and neutrons in the nucleus. Subatomic Particles, the Nucleus and Isotopes Subatomic particles, the nucleus and isotopes
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