3. Elements are arranged by atomic number
Vertically
into Groups
Horizontally Into
Periods
4. Draw electron configuration diagrams to show the electron
arrangements for these elements on the periodic table provided
remember 2,8,8,2
Do this for the first
twenty elements
before the next slide.
5. Make a conclusion: Look at the
diagrams you drew for each group . . .
Each atom has the same number of
electrons in it’s outermost shell.
These electrons are called valence
electrons. Valence electrons determine
how an element will form chemical
bonds and react.
6. For example - the Group 2 elements all have 2
valence electrons.
Be (Beryllium)
Atom
Mg (Magnesium) Atom
7. • The number of outer or “valence” electrons in an
atom effects the way an atom bonds.
• The way an atom bonds determines many properties
of the element.
• This is why elements within a group usually have
similar chemical properties.
For example alkali (group 1) metals all
react with water to produce hydrogen gas
8. If you looked at an atom from each element in
a period
What do you see…
Each atom has the same number of
electron holding shells.
9. For example: the period 4 atoms each have 4 electron
shells
4
K (Potassium) Kr (Krypton)
Atom Atom
Fe (Iron) Atom
10. Now, use a different color and write the 2,8,8,2
electron arrangements for the first 20 elements on
your handout.
1 2
2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8
2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8
What do you observe?
2,8,8,1 2,8,8,2
The last number in the electron arrangement
indicates the number of valence electrons.
This is the same for all elements in a group.
