Electronic structure: 288 rule

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  1. Introduction to electronic structure
  2. Analysing the structure of the atom.
  3. The 2-8-8 Rule: Walkthrough
  4. A shortcut to the periodic table: predicting electron shells
  1. Apply your knowledge of electron shells to find the electron configuration of elements.
    Give the electronic structure for an atom of the following chemical elements:
    1. i) B
      ii) Si
    2. i) Mg
      ii) Ar
      iii) F
  2. Use the electron configuration to identify elements of the Periodic Table.
    Which chemical element would display this electron shell configuration?
    1. i) (2,2)
      ii) (2,7)
    2. i) (2,8,1)
      ii) (2,8,7)
Topic Notes
In this lesson, we will learn:
• A method to determine electronic structure in atoms.
• The reason electronic structure is important to understanding chemical elements.
• How to predict the number of outer shell electrons in elements.


Electrons in atoms exist outside the nucleus in energy levels sometimes known as shells. The number of electrons in an atom's outer electron shell is called the electron shell configuration.

• The reactivity of an element is strongly linked to the number of outer shell electrons an atom of the element has. Elements react in ways to obtain a full outer shell, whether by sharing, losing or gaining electrons (see our videos on bonding and types of compounds).

• The 1st, 2nd, and 3rd shells can hold 2, 8 and 8 electrons respectively. Once a shell is filled up, any further electrons must fill in a new higher level shell.

• The number of outer shell electrons is a defining factor of how the periodic table is laid out: elements in the same group have the same outer shell electron configuration.