## Valence electrons and Lewis diagrams

Now that we understand a bit more about bonding we need to refresh the concept of Lewis diagrams that you learnt about in Grade \(\text{10}\). With the knowledge of why atoms bond and the knowledge of how to draw Lewis diagrams we will have all the tools that we need to try to predict which atoms will bond and what shape the molecule will be.

In grade \(\text{10}\) we learnt how to write the electronic structure for any element. For drawing Lewis diagrams the one that you should be familiar with is the spectroscopic notation. For example the electron configuration of chlorine in spectroscopic notation is: \(1\text{s}^{2}2\text{s}^{2}2\text{p}^{5}\). Or if we use the condensed form: \([\text{He}]2\text{s}^{2}2\text{p}^{5}\). The condensed spectroscopic notation quickly shows you the valence electrons for the element.

Using the number of valence electrons we can easily draw Lewis diagrams for any element. In Grade \(\text{10}\) you learnt how to draw Lewis diagrams. We will refresh the concepts here as they will aid us in our discussion of bonding.

#### Tip:

A **Lewis diagram** uses dots or crosses to represent the **valence electrons** on different atoms. The chemical symbol of the element is used to represent the nucleus and the core electrons of the atom.

Lewis diagrams for the elements in period \(\text{2}\) are shown below:

Element | Group number | Valence electrons | Spectroscopic notation | Lewis diagram |

Lithium | \(\text{1}\) | \(\text{1}\) | \([\text{He}]2\text{s}^{1}\) | |

Beryllium | \(\text{2}\) | \(\text{2}\) | \([\text{He}]2\text{s}^{2}\) | |

Boron | \(\text{13}\) | \(\text{3}\) | \([\text{He}]2\text{s}^{2}2\text{p}^{1}\) | |

Carbon | \(\text{14}\) | \(\text{4}\) | \([\text{He}]2\text{s}^{2}2\text{p}^{2}\) | |

Nitrogen | \(\text{15}\) | \(\text{5}\) | \([\text{He}]2\text{s}^{2}2\text{p}^{3}\) | |

Oxygen | \(\text{16}\) | \(\text{6}\) | \([\text{He}]2\text{s}^{2}2\text{p}^{4}\) | |

Fluorine | \(\text{17}\) | \(\text{7}\) | \([\text{He}]2\text{s}^{2}2\text{p}^{5}\) | |

Neon | \(\text{18}\) | \(\text{8}\) | \([\text{He}]2\text{s}^{2}2\text{p}^{6}\) |

#### Tip:

You can place the unpaired electrons anywhere (top, bottom, left or right). The exact ordering in a Lewis diagram does not matter.