# Lewis Dot Diagram

Lewis Dot Diagram and Octet Rule
6:06 — by Leah F.

Tip: This isn't the place to ask a question because the teacher can't reply.

## Key Questions

• Created by Gilbert Lewis, Lewis Dot Diagrams are simple models to represent the arrangement of electrons in atoms that explain and predict empirical formulas.

The model is simply the symbol for the ele![enter image source herement representing the nucleus plus all the electrons except the valence electrons.

The valence electrons (represented by the last digit of a group number on the periodic table), change and are shown as dots around the central symbol , with the entire diagram showing (for an atom) a net charge of zero.

These diagrams are an extremely useful model to help describe how atoms bond.

To draw Lewis symbols for main groups of atoms:

1. Write the element symbol to represent the nucleus and any filled energy levels of the atom.

2. Add a dot to represent each valence electron.

3. Start by placing valence electrons singly into each of four valence orbitals (represented by the four sides of the element symbol).

4.If additional locations are required for electrons once each orbital is half-filled, start filling each of the four orbitals with a second electron until up to eight valence electrons have been represented by dots.

For example: Oxygen has 6 valence electrons .

Electron Energy Level Diagram of an Oxygen Atom:

6e-
2e-
8p+
O
Oxygen Atom

Since Oxygen has 6 valence electrons, to represent the atom in a Lewis Dot Diagram you would take the central atom, which is O and surround it with 6 dots.

()

It is important to understand that Lewis symbols do not mean that electrons are dots or that they are stationary. The four sides of the atomic symbol just represent the four valence level space regions (orbitals) that may be occupied by electrons. The dots simply keep count of how many electrons are in each orbital (or not).

Source: Nelson Chemistry Textbook.

How else but by counting up (i) the number of valence electrons on the neutral atoms, and (ii) the charge on the atom or ion............?

#### Explanation:

Now we build Lewis structures by elaborating from neutral atoms, and of course, we have to account for the charge on the atom or radical ion.

Take for example $\text{nitrate ion}$, $N {O}_{3}^{-}$. Nitrogen, Group V, has 5 valence electrons; oxygen, Group VI, has 6 valence electrons. And we throw in another electron, so that we have $5 + 3 \times 6 + 1 = 24$ $\text{valence electrons}$, i.e. $\text{12 electron pairs}$ in the Lewis structure of $N {O}_{3}^{-}$ to distribute around 4 centres.

And thus we get $O = {N}^{+} {\left(- {O}^{-}\right)}_{2}$. From the left, around the doubly bound oxygen there are $2 + 2$ lone pair electrons on oxygen, (i) $4$ electrons, and in the $O = N$ bond, (ii) $4$ electrons, NO lone pairs on the cationic, quaternized nitrogen, and (iii) $2 \times 8 = 16$ electrons on the formally singly bound oxygens, each of which bears a NEGATIVE charge: thus 24 valence electrons as required for the Lewis structure.

So all we do is to take the number of valence electrons (which is given by the atom's Group number), and add these numbers together, and add or subtract depending on the negative or positive charge of the species.

Can you do the same for $P {O}_{4}^{- 3}$? There must be 32 electrons to distribute, i.e. 16 electron pairs.

• In a Lewis structure, atoms that are bonded covalently are represented by a single line joining the two atoms, which are represented by the element's chemical symbol. Covalent bonds occur mainly in diatomic molecules, such as hydrogen, nitrogen, fluorine, chlorine, bromine, iodine, and astatine.

The Lewis dot diagram for the covalent bonding of chlorine, ($C {l}_{2}$), would be:

When atoms are bonded ionically, the bond is represented by two dots between the element's chemical symbols. Ionic bonds are formed between charged particles (ions), so an example of an ionic compound would be NaCl, whose Lewis structure is:

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