CH 1.3 IONS AND THE OCTET RULE
The Octet Rule
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Elements with a full valence shell have a special stability. (ex. The noble gases)
In the first 18 elements a full valence shell (except the 1 st shell) contains 8 electrons.
This is known as a full/stable octet. The exception is Helium which is stable with 2 electrons
in its valence shell.
All other atoms do not have full valence shells, but they try to obtain this electron
arrangement by combining with other elements.
There are three ways that atoms can achieve a full octet: Share, Lose or Gain electrons.
When atoms lose or gain electrons they form Ions: an atom with a positive or negative
charge.
Formation of Ions
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Positive Ions: Ca ions
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The metals, which are located to the left of the staircase line on the periodic table tend to
lose valence electrons in order to achieve a full octet. In doing so, metals will become
positively charged ions.
Let’s consider: Sodium and Aluminum for example.
ATOM
ION
VALENCE
ION SYMBOL
Sodium
Aluminum
Negative Ions: Anions (onions make you cry)
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The elements on the right hand side of the staircase are mostly nonmetals, which tend to
gain electrons in order to fill there almost-complete valence shells. In doing so, they
become negatively charged ions.
Let’s consider: Fluorine and Oxygen
ATOM
ION
VALENCE
ION SYMBOL
Fluorine
Oxygen
In General
Metals: ________ electrons to become ________ with the same electron configuration as the
nearest noble gas with a smaller atomic number.
Nonmetals: _________ electrons to become _________ with the same electron configuration as
the nearest noble gas with a larger atomic number.
Elements with Multiple Ionic Charges
Multivalent: The property of having more than one possible ionic charge/valence.
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Most of the transition metals (middle of the periodic table) are multivalent, and can form
more than one stable ion.
When naming these elements you must use a __________________ in brackets following
the metal to indicate its charge. (ex. Copper (I) or Copper (II) ) (see table 1, p.19).
Polyatomic Ions
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These are ions which consist of more than one atom. (ex. Phosphate ion PO 43- ,
Nitrate ion NO3- )
Most polyatomic ions are composed of oxygen, nitrogen, phosphorous, sulfur, chlorine and
carbon. They are mostly anions, by gaining one or more electrons.
A polyatomic ion behaves just like an ion, made up of only one atom.
Ions in the Human Body
 99% of your body is made up of only 6 elements! (O, C, H, N, Ca, P) and much smaller
quantities of S, Cl, Na, Mg, I and Fe. (see table 3, p.21)
 Sometimes polyatomic ions can have negative effects on the environment and our health.
Ex. Phosphates in lakes/ponds cause algae blooms. Nitrates in processed foods form
cancer-causing agents when they react with substances in the digestive system.
 However, some polyatomic ions occur in nature and are essential to our health. Ex.
Calcium phosphate found in bones and teeth, and Hydrogen carbonate help regulate blood
pH.