Valence Electrons (Use the periodic table on page 504 to help you do this page)
The electrons farthest from the nucleus and at the highest energy state are called the
valence electrons. The valence electrons are the electrons that form chemical bonds
between 2 or more atoms. Look at the element Lithium. It is in the second row (period)
of the table. How many protons does Li have? 3 How many electrons does it have? 3.
How many electron shells does it have? 2. How many electrons are in its first shell? 2.
How many electrons are in its second shell? 1. Lithium has how many valence (outer)
electrons? 1.
One important way to represent the valence electrons and to predict the kind of chemical
compounds it will make is to draw an electron dot diagram.
An electron dot diagram looks like this for Li:
Notice that we write the symbol
for Lithium and one dot to represent the one valence electron. Here is the electron dot
diagram for Chlorine:
How many valence electrons does chlorine have? 7.
Remember these are the electrons in the third shell of chlorine. Chlorine will have how
many electrons in its first shell? 2. How many electrons are in its second shell? 8_.
Make electrons dot diagrams for all the elements from Hydrogen to Argon below.
Here are the rest!
How many valence electrons total can the first row (period) hold? 2.
How many valence electrons total can the second row (period) hold? 8.
How many valence electrons total can the third row hold? 8.
Every row of the periodic table (except the first) can hold 8 valence electrons. That
includes elements 19 (Potassium) and up, although you can see that many electrons are
filled to complete a row (period) for those elements. In fact elements in periods 4 though
7 of the periodic table fill electrons in lower shells as you progress across the table, but
these electrons are not involved in bonding. In other words they are not valence
electrons. The rules for how these elements make bonds with other atoms are a bit more
complicated. In fact you will learn in more advanced chemistry classes that electrons
actually fill spaces called different orbitals that make up the shells for all the atoms. But
the rule still holds that every row of the periodic table can hold up to a total of 8 valence
electrons. This rule is called the octet rule. What do you think octet means? eight.
What are the valence electrons? outer shell or highest energy electrons.
Why are they important? they are the electrons involved in chemical bonding.