Reactivity and Valence Electrons
THE OCTET RULE
Focus Question: Why are some elements more reactive than others?
Remember that you can determine the number of valence electrons for an element by using the periodic
table.
1. Label the number of valence electrons of elements in each column.
2. Why can’t you determine the valence number of transition metals by looking at the periodic table?
3. How are hydrogen and helium different from other elements in terms of valence electrons?
Use patterns of reactivity from the last unit – what was the most reactive metal? most reactive nonmetal?
How are reactivity and number of valence electrons connected?
THE OCTET RULE
The attraction of elements toward having eight valence electrons whenever possible is known as the octet
rule. This rule allows chemists to predict the placement of electrons around the nucleus, identify electrons
added or lost during chemical reactions and predict the chemical reactivity of atoms based upon their
particular electron configuration.
It’s a very useful rule, but you should know that there are MANY bonding situations where it does NOT apply.
In general, it works for alkali metals and alkaline earth metals and nonmetals, but not for the transition metals.
And not all nonmetals or metals can satisfy the octet rule. Some atoms can even be surrounded with more
than 8 valence electrons. As a result, the rule must be used with caution.
Check out this smaller version of the periodic table (it’s missing the transition elements).
How many electrons are elements in each group looking to gain or lose to become stable?
LEWIS DOT STRUCTURES
Valence electrons can be shown around an element using Lewis Dot structures. The Lewis
structure was named after Gilbert N. Lewis, who introduced it in his 1916 article The Atom and the
Molecule. They are very useful tools in chemistry because they allow you to determine the type of
bond an element will make as well as predict the type of ion that it will form.
Draw a Lewis Dot structure for YOUR element on a 3x5 card.