8.1. Ions http://www.ck12.org
TABLE8.1:Electron Configuration
Element Electron Configuration Number of Valence Electrons
lithium 1 s^22 s^11
beryllium 1 s^22 s^22
nitrogen 1 s^22 s^22 p^35
neon 1 s^22 s^22 p^68For elements in thesandpblocks, the number of valence electrons can easily be determined from the group number.
In thesblock, Group 1 elements have one valence electron, while Group 2 elements have two valence electrons.
In thepblock, the number of valence electrons is equal to the group number minus ten. Group 13 elements have
three valence electrons, Group 14 elements have four, and so on. The noble gases in Group 18 have eight valence
electrons, and the full outersandpsublevels are what give these elements their special stability.
When examining chemical bonding, it is necessary to keep track of the valence electrons on each atom. Anelectron
dot diagramshows the valence electrons of an atom as dots distributed around the element’s symbol. For example,
a beryllium atom, which has two valence electrons, would have the electron dot diagram below.
Since electrons repel each other, the dots for a given atom are distributed evenly around the symbol before they are
paired. The table below (Table8.2) shows the electron dot diagrams for the entire second period.
TABLE8.2: Electron Dot Diagrams for the Second Period Elements
Group Number Electron Dot Diagram
1