How to work out the number of protons, neutrons and electrons in an atom.......... |
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Li If you look at Lithium in the periodic table you will notice that it has two numbers, 3 and 7. The number 3 is the atomic number and the number 7 is the mass number.
The atomic number tells us that it has It has 3 protons and also 3 electrons because the number of protons and electrons in an atom must always be equal.
The mass number is the number of protons and neutrons, so if out of a total of 7, 3 are protons, then the rest must be neutrons. Lithium has 4 neutrons, (7-3).
The diagram below shows a lithium atom. Protons are white circles in the nucleus, and electrons are white circles outside the nucleus, neutrons are black circles.
