Atoms form ions by gaining or losing electrons to achieve a full outer shell like noble gases. Sodium loses 1 electron to form Na+ with 10 electrons and a positive charge as a cation. Fluorine gains 1 electron to form F- with 10 electrons and a negative charge as an anion. An element's group number helps determine its ionic charge when forming cations or anions to achieve a full outer shell.

1. Ion Formation

2. In order for an atom to feel
“stable” it wants to have…
• A full outer shell of electrons!
• Look at the following atoms, circle the atoms that
are the most stable…
• Noble gases (group 8) are the most stable,
because they all naturally have full outer shells

3. Most atoms do not have full
outer shells…
• So they can gain or lose electrons to get there!
Na+1
Protons= 11
11+
Electrons= 10
(lost 1 electron)

4. -1
F
Protons= 9
9+
Electrons= 10
(gained 1 electron)

5. Will these atoms gain or lose
electrons?

6. Two types of Ions…
Cation Anion
Ion with a POSITIVE Ion with a NEGATIVE
charge. charge.
CA+ION ANION

7. An elements Group will help
determine it’s ionic charge…

8. Same
# of
number of
# of # of electrons
Ion Name Ion Symbol electrons
Protons Electrons gained or
as which
lost
noble gas?
Fluoride
16 18
20 Lost 2