
UNIT # 3
Introduction
Objectives
Reading
3.1 Structure of the Atom 3.2 Isotopes 3.3 Arrangement of Electrons 3.4 Electron Configura tions 3.5 Atomic Mass
Problems 1 \| 2 \| 3

ATOMIC STRUCTURE

3.3 - Arrangement of Electrons

3.3.2 - The 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 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 (see below and also section 4.2) . Take a look at the rules for writing Lewis electron-dot symbols.

The end result is, for representative elements belonging to:

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

In summary, view the Lewis electon-dot symbols for the representative elements belonging in the various groups.

Section 4.7
Electron-Dot Formulas of Elements ..p89

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ATOMIC STRUCTURE 3.3 - Arrangement of Electrons

ATOMIC STRUCTURE

3.3 - Arrangement of Electrons