Lewis Dot Diagrams
Science 10
Mr. Dawson
1
Energy in the atom
• Charged particles called electrons surround
the nucleus in regions called shells or energy
levels
2
Second Row – (2nd energy level)
∙
Li
∙
Be∙
∙
B∙
∙
∙
∙C∙
∙
∙∙
∙N∙
∙
∙∙
∙O:
∙∙
∙∙
∙F:
∙∙
∙∙
:Ne:
∙∙
Electrons are added one at a time starting at 12 o’clock then
3, 6, 9 o’clock. Electrons do not pair until the 5th electron
which is back to 12 o’clock. After 8 electrons there are 4 pairs
of electrons which means this valence shell is full. The next
shell out will begin to fill. Electron in the valence shell are
called valence electrons. Notice the number of valence
electrons and the group number. (Do you see a relationship?)
3
• Atoms of different
elements have different
numbers of electrons
• Each shell is “full” before
electrons move to the
next shell. Sodium has to
inner shells and the outer
(valence shell). The 1st
and 2nd shells (inside
shells) are full and the 3rd
shell (valence shell) has
one electron. This one
electron in the valence
shell is called a valence
electron.
4
The Periodic Table and Electron Dot symbols
(Lewis Structures)
• Period number: gives the number of electron
energy levels (valence shell last one out)
• Energy levels will fill in the following order: 2,
8, 8, 8….(valence shell last one out)
• Group number: number of valence electrons
(look at the second digit of the group number)
5
Trends:
• Elements of the same group have similar
properties because they have the same
number of electrons in their outer shell.
• The outer shell = valence shell
• Electrons that occupy the valence shell are
called valence electrons
6
Noble gas configuration
• Group 18, the noble gases are the most stable of
elements because their valence shell is full with
electrons
• Less energy required
• During chemical changes atoms will change in electron
configuration (the arrangement of valence) to try to get
a full valence shell.
• Metal atoms have few valence electrons and will lose
valence electrons leaving a full inner shell (metals are
born losers)
• Non-metal atoms have larger number of valence
electrons (close to full) and tend to gain electrons.
(Non-metals are winners)
7