Atomic number and mass number | Chemistry | Fuse School

How do we tell elements apart from each other? Find out in this video from the Properties of Matter chapter of the Virtual School GCSE Chemistry. 00:00:05,920 -- 00:00:09,550 When you look at the periodic table you will see that each element has its own box, and 00:00:09,550 -- 00:00:16,550 within that box, you will find two numbers. The atomic number, or proton number, and the 00:00:17,480 -- 00:00:24,480 mass number, but what do these numbers mean? The atomic number has the symbol 'z', 00:00:27,220 -- 00:00:33,280 this number tells you how many protons are in one atom of an element. The number is always 00:00:33,280 -- 00:00:40,280 the same for all atoms of a particular element. Atoms of different elements have different 00:00:40,580 -- 00:00:45,250 atomic numbers, meaning they have different numbers of protons. 00:00:45,250 -- 00:00:52,250 For example, an atom of Hydrogen has an atomic number of 1 because it has 1 proton, but an 00:00:53,720 -- 00:01:00,720 atom of Oxygen has and atomic number of 8 because it has 8 protons. 00:01:01,659 -- 00:01:07,640 The next number we look at is the mass number. The mass number has the symbol A. 00:01:07,640 -- 00:01:14,640 The mass number tells you how many protons and neutrons are in one atom of an element. 00:01:16,439 -- 00:01:23,439 We need to remember that Protons and Neutrons each have a relative mass of 1 and that Electrons 00:01:25,130 -- 00:01:31,030 are so small, that their mass does not need to be considered in the mass number of an atom. 00:01:31,030 -- 00:01:38,030 So if we know the mass number of an element, and we know the atomic number, we can calculate 00:01:38,149 -- 00:01:44,299 the number of Neutrons in an atom of a particular element. 00:01:44,299 -- 00:01:51,299 So the Mass Number = The Atomic Number + the Number of Neutrons. The Atomic Number is just the number of Protons and Atoms, therefore, 00:01:55,990 -- 00:02:02,990 The Mass Number = protons + neutrons. So if we take oxygen, 00:02:04,090 -- 00:02:11,090 Oxygen has a mass number of 16 and 8 Protons, how many neutrons does it have? 00:02:12,530 -- 00:02:19,530 Remember, Mass Number = protons + neutrons We can rearrange this to show that 00:02:20,569 -- 00:02:27,569 Neutrons = Mass Number - Atomic Number. Neutrons = 16 - 8 00:02:31,189 -- 00:02:36,700 = 8 Oxygen therefore has 8 neutrons. 00:02:36,700 -- 00:02:39,409 Let take another example, 00:02:39,409 -- 00:02:46,409 Lithium has a mass number of 7 and an atomic mass of 3, how many neutrons does it have? 00:02:47,040 -- 00:02:52,090 Mass Number = protons + neutrons We can rearrange this to show that 00:02:52,090 -- 00:02:59,090 Neutrons = Mass Number - Atomic Number Neutrons = 7- 3 00:02:59,299 -- 00:03:05,640 = 4 Lithium therefore has 4 neutrons. 00:03:05,640 -- 00:03:12,230 So the atomic number is the number of protons in an atom and the mass number is the number 00:03:12,230 -- 00:03:14,719 of protons and neutrons in an atom. This is part of our sciences pilot for the virtual school. We would appreciate any comments or feedback. Want to learn more? Visit: www.thevirtualschool.com This video is distributed under a Creative Commons License: Attribution-NonCommercial-NoDerivs CC BY-NC-ND Also, make sure to follow us on Twitter: https://twitter.com/virtualschooluk and subscribe to interesting posts on Edutech and ICT4E on http://thevirtualschool.wordpress.com/