Electronic Structure

• Electrons surround the atomic nucleus in regions called shells.

  The shell closest to the nucleus can hold 2 electrons, whereas the outer ones can hold up to 8 electrons
• An atom of potassium has 1 electron in its outermost shell. 

  In a chemical reaction, will potassium gain or lose 1 electron?

  lose

  Atoms are unstable when they have an incomplete shell of electrons. This means potassium will 'want' to lose one electron, leaving it with three complete shells
• An atom of oxygen has 6 electrons in the outer shell. In a reaction, it gains 2 electrons. 

  What is the charge of the oxide ion created?

  The oxygen atom will still have 6 protons, but will now have 8 electrons. This means it will have 6 + charges, and 8 - charges, meaning 2- overall. 
• Where are the electrons located in an atom?

  Electrons are found in shells (or 'energy levels'), and orbit the nucleus.
• What do we mean by the ‘electronic structure’ or ‘electronic configuration’ of an atom?

  Electronic structure’ or ‘electronic configuration’ refers to the arrangement of electrons within an atom, i.e. how many electrons are in each shell.
• How many electrons are found in the first, second, and third shells of an atom?

  1st shell: 2 electrons  2nd shell: 8 electrons  3rd shell: 8 electrons
• If an atom has 15 electrons in total, how many will it have in each shell? 


  2 in the first shell

  8 in the second shell

  5 in the third shell
• What is meant by an atoms ‘outer shell’?

  The 'outer shell' is the shell of electrons that is furthest from the nucleus.