electron structure

• electrons in atoms are arranged in shells
• a sodium atom has two electrons in the first shell, nearest to the nucleus, eight electrons on the next shell ; and one electron on the outer shell.
• atoms of all elements in the same group of the periodic tablehave the same number of outer shell electrons
• group 1 elements have 1 electron in the outer shell, and group 7 elements have 7 electrons in the outer shell
• the number of outer shell electrons gives elements their chemical properties
• atom with less then 8 on the outer shell = unstable, meaning that it wants to react with another atom so it can have a full outer shell