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Module 3 Revision notes - Atomic Structure & The Periodic Table
These notes are not intended as a complete set of revision materials; instead they are here to give you a quick reminder of the most important points in this module.
The mass and charge of these subatomic particles is as follows:
Remember: the charge on a proton is positive, the charge on neutron is neutral (0) and . . . . the charge on an electron is negative.
How many protons, neutrons and electrons does an atom have?
You can work this out using the periodic table. Every element in the periodic table has two numbers with it: the atomic number and the mass number. For example for lithium, the numbers are:
The atomic number is the number of protons that the atom has. It is also the number of electrons that the atom has. So lithium has 3 protons and 3 electrons.
The mass number is the number of protons and neutrons added together. So, for lithium there are 7 protons and neutrons combined, and we know that 3 of them are protons so there must be 4 neutrons.
RULE: The number is neutrons is (mass number - atomic number)
How are the electrons arranged?
The electrons are arranged in energy levels (or electron shells as they are sometimes known). The number of electrons that you can fit into each energy level is as follows:
You need to be able to work out the electron configuration of the first 20 elements in the periodic table. We write electron configurations like this:
which means that there are 2 electrons in the first energy level, 8 in the second energy level and 1 in the third energy level. Here is a complete list of the electron configurations of the first 20 elements:
The Periodic Table
As you move through the elements in a group the REACTIVITY (hoe reactive they are) changes. The way that it changes depends on the group you are looking at:
POTASSIUM > SODIUM > LITHIUM
FLUORINE > CHLORINE > BROMINE > IODINE
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