Isotopes and the importance of proton numbers

• The electron orbits of these two elements is small and can only carry two electrons
• The next element in the series is lithium
• It comes with two electronic shells
• The second outer shell can hold 8 electrons
• Lithium has a proton number of three and has one electron in the outer shell
• The way in which the electrons are arranged determines the reactions of the elements
• The movement of electrons from one atom to another gives elements their chemical properties
• Atoms of the same element are the same
• They behave in the same way in a chemical reaction
• Electrons can only escape from their orbits if energy is supplied
• If they can do so easily then the element is very reactive

The nucleon number and isotopes

• The proton number of an element does not include the number of neutrons in an atom
• Because neutrons have no charge, an excess of them does not affect the charge of a nucleus
• Some atoms have the same number of protons and electrons but a different number of neutrons
• These atoms are known as isotopes
• Isotopes have the same number of protons but a different number of neutrons
• For example Chlorine 35 has 17 protons and 18 neutrons
• and Chlorine 37 has 17 protons and 20 neutrons
• These two are isotopes

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