Lewis electron-dot symbols of elements
Gilbert N. Lewis is widely known for his use of simple symbolic representations of elements that show valence electrons as dots. You've seen what the are Bohr diagrams for the first 20 elements. Sometimes it is more convenient to represent the elements by its Lewis electron-dot symbol. It is not to say one is better than the other. The Bohr diagrams show arrangement of all the electrons.
The Lewis electron-dot symbols focus on the electrons in the highest principal energy level in the atom, the valence electrons. After all, these are the electrons that participate in chemical reactions. Lewis electron-dot symbols work well for the representative elements.
Contents
Rules for writing electron-dot symbols of elements
1. Write the symbol for the element. The symbol represents the nucleus and the inner or core electrons for the element. In the image below, a generic symbol, X, is used. There are four sides surrounding the symbol.
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2. Determine the number of valence electrons for the element. Use a dot to represent an electron.
3. Assign a dot to each side of the symbol up to a maximum of four valence electron.
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| 1 valence electron | 2 valence electrons | 3 valence electrons | 4 valence electrons |
(Helium is an exception, with both valence electrons paired up on the same side of the symbol.)
4. For assigning more than 4 valence electrons, start pairing up electrons on the four sides to a maximum of eight electrons.
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| 5 valence electron | 6 valence electrons | 7 valence electrons | 8 valence electrons |
The number of dots you have around the symbol represents the actual number of valence electrons for the element.
Representative elements
| Representative Elements in: | Number of Valence Electrons |
|---|---|
| Group IA | all elements have 1 valence electron |
| Group IIA | all elements have 2 valence electrons |
| Group IIIA | all elements have 3 valence electrons |
| Group IVA | all elements have 4 valence electrons |
| Group VA | all elements have 5 valence electrons |
| Group VIA | all elements have 6 valence electrons |
| Group VIIA | all elements have 7 valence electrons |
| Group VIIIA | all elements have 8 valence electrons |
Symbols
| Group IA
X = H, Li, Na, K, Rb, Cs, Fr |
Group IIA
X = Be, Mg, Ca, Sr, Ba, Ra |
The exception is He.
X = He |
| Group IIIA
X = B, Al, Ga, In, Tl |
Group IVA
X = C, Si, Ge, Sn, Pb | |
| Group VA
X = N, P, As, Sb, Bi |
Group VIA
X = O, S, Se, Te, Po | |
| Group VIIA
X = F, Cl, Br, I, At |
Group VIIIA
X = Ne, Ar, Kr, Xe, Rn |
Content suitability
BCIT courses: CHEM 0011
