Beginning Organic Chemistry (BOC)
1. Basic Knowledge
b. Electronic Structure of Atoms

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The Electronic Structure of the Atom.

As you recall, atoms seem to be made up of a very tiny, positively charged nucleus surrounded by negatively charged electrons. The number of electrons varies from atom to atom according to the number of positive charges on the nucleus; it is the number of electrons and their spacial distribution which gives the different chemistry of the atoms.

In a very simple way, electrons in an atom can be considered to come in layers, with only the outermost layer influencing the chemistry.

In the periodic table, elements with the same outer layer of electrons, and thus with similar chemical properties, are placed in columns:

IUPAC Group Number
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Li B C N O F
[Na] Mg [Al] P S Cl
[Ni] Cu [Zn] Br
[Pd] I
[Pt] Hg
1 2 2 3 4 5 6 7
Number of electrons in outer layer.

Go deeper into electronic structure of atoms.

Atom groups with similar chemistry

Because atoms in a column have a similar chemistry, it is very common to speak of a column as a family of elements. The column 17 group of atoms, for example, is known as the 'halogens'.

The octet rule.

Again in a simple way, the chemistry of an many of the elements involved in organic molecules can be described by looking at how atoms add, lose or share pairs of, electrons to make a total of eight (8) in their outer layer.


Note that hydrogen, H, is an exception to this. It requires only two (2) electrons in its only electron layer.

Atoms with less than four (4) electrons cannot, in a simple way, gain the octet of electrons in their outer layer by sharing electron pairs to form neutral compounds.

However, for most of the atoms involved in organic molecules the octet rule holds.

Date created: 2005 06 08.