How to Create Lewis Dot Diagrams

Purpose: The purpose of Lewis Dot Diagrams is to display an elements valence electrons in a short hand way. These valance electrons determine what chemical families and groups (vertical columns) different elements fall into. The arrangement of these valance electrons tell us about the properties of elements, as well as how element behave in chemical reactions.

How To: 1) Determine the number of valance electrons. This can be done 2 ways. First, you can create the Bohr model for the element and look at the number of valance electrons.

Let’s try Carbon here:

Secondly, and way more efficiently, is to do a quick calculation to determine the number of valance electrons. Period 1 Elements: Simply take the # of electrons because they only have 1 shell. Period 2 Elements: Total # of electrons - # of electrons in first shell = # of valance electrons. Period 3 Elements: Total # of electrons – # of electrons in first shell - # of electrons in second shell = # of valance electrons.

Let’s try: Hydrogen Period 1: 1 valence electron Carbon Period 2: Total # electrons =_____ # of electrons in 1st shell = _____ # of valence electrons = _____ _____- _____= _____   Silicon Period 3: Total # electrons = _____ # of electrons in 1st shell = _____ # of electrons in 2nd shell = _____ _____ - _____ - _____ = _____

2) Use the Chemical Symbol In Lewis dot diagrams, the chemical symbol of an atom represents the nucleus, plus all other inner (non-valance) electrons.

3) Dots and where you place them Each dot in the diagram represents a valance electron. You want to fill them in a clockwise fashion, placing 1 on each side. This means starting at the top, then doing to the right, then the bottom and finally the left. Only after you have placed an electron in each of these spots do you continue on to the top. You keep following that pattern until you have no more valance electrons.

Let’s try a few examples: Sodium - 1 valence electron, 1 starts at the top

Beryllium - 2 valence electron, 1 starts at the top, the next goes to the right 

Neon - 8 valence electrons, full shell Neon - 8 valence electrons, full shell. Started adding electrons at the top and proceeded in a clockwise fashion.

This shows you the steps on how the electrons are added This shows you the steps on how the electrons are added. Notice that the first 4 are added one at a time in a clockwise fashion. (A to D)Then the next 4 are added afterwards. (E to H)

4) Charges of elements The number of electrons left in the outer shell, determines the charge of an atom. You need to look at whether it is easier for an element to loose electron(s) (making it’s charge positive overall) or gain electron(s) (making it’s charge negative overall).

Let’s use the examples from the previous part to determine their charge. Sodium: Easier to lose 1 electron, therefore the charge is +1

Beryllium: Easier to lose 2 electrons, therefore the charge is +2

Neon: Does not want to lose or gain any electrons, no charge

5) Chemical Families No matter what period an element is in, it will have the same number of valance electrons as all other elements in its’ chemical family or group. For example, if you know the # of valance electrons in Lithium (1st element in the Alkali metals), then you know the # of valance electron for Francium (Last element in the Alkali metals) .