Electron-Dot Symbols:

The electron-dot symbols for atoms show the symbol for the element and the number of valence electrons represented as dots. This representation helps us predict the number of electrons a metal will lose. It also helps us predict the number of electrons a nonmetal will gain.

Metals: Main-group metals typically lose their valence electrons in reactions to form the octet of the previous period rare gas . A lithium atom with 3 electrons 1s² 2s¹ or [He] 2s¹ will lose its one outer electron to form the helium core [He].

Example: What is the electron-dot symbol for sodium, Na, and what kind of ion does it form?

Answer: Sodium is in group 1A. The electron dot formula for sodium is Na^. . This is explained by the fact that sodium has the electron configuration 1s²2s²2p⁶3s¹. Sodium loses the 3s electron and forms the neon rare gas octet which is 1s²2s²2p⁶.

When sodium atoms lose one electron they form a sodium +1 ion, Na¹⁺ (notice there is no dot for the cation).

Non-metals: Main-group nonmetals typically add to their valence electrons in reactions to form the octet of the period rare gas. Typically the nonmetals in group 5A gain three electrons, those in group 6A gain two electrons and those in group 7A gain one electron.

Example: What is the electron-dot symbol for nitrogen, N, and what kind of ion does it form?

Answer:

Nitrogen is in group 5A. It is a nonmetal. The electron dot formula for nitrogen looks like this with five 'dots'.

This is explained by the fact that nitrogen has the electron configuration 1s22s22p3. Nitrogen has five valence electrons. It needs three electrons to complete the octet for 2s2p subshells. When nitrogen gains three electrons, it forms the nitride N3- ion, . Nitrogen completes the neon rare gas octet which is 2s22p6. Nitrogen is in the second period and neon is at the end of the second period (notice there are eight dots for the N3- anion).

 Created by Dr. Walt Volland revised July 12 , 2013 all rights reserved