Ions and Ionic Bonding
What are ionic compounds and how do they form?
Noble Gases
For the noble gases, the outer shells (energy levels) are full.
Helium has 2 electrons in its outer shell, the most it can hold.
Neon and argon have 8 electrons in their outer shells, the most
that they can hold.
The noble gases are “stable.”
They do not react with other elements to form compounds.
Sodium
When elements form compounds, the way in which electrons are arranged around the
element change.
For example, let’s start with sodium.
This atom has 11 electrons.
The outer shell has 1 electron.
This atom is not stable.
Sodium Atom and Ion
If sodium gave away 1 electron, then it would be stable.
When sodium gives away one electron, it has 8 electrons
left in its outer shell.
Now it resembles neon with 8 electrons in the outer shell.
When it was neutral, sodium had 11 electrons and 11
protons. When it gives away 1 electron, it has only 10
electrons.
With 11 protons (+11) and 10 electrons (-10), the sum +11 +
-10 = +1.
Now sodium is not neutral. It has a net charge of +1. It is
now a positive ion.
Ions are atoms (or groups of atoms) that carry a charge.
All positive ions are called cations. The symbol for the
sodium ion is Na+.
Chlorine
Now let’s look at chlorine.
This atom has 17 electrons.
The outer shell has 7 electrons.
This atom is not stable.
