Ions
Wandering electrons
• In the last few weeks, we talked about the
balance between protons and electrons in a
neutral atom.
Atomic Model Reminders
1
H
1.00794
1p+
e-
Wandering electrons
• In the last few weeks, we talked about the
balance between protons and electrons in a
neutral atom.
• What happens if we have an electron that
leaves an orbital? What happens to that
atom?
Atomic Model Reminders
1
H
1.00794
1p+
e-
Well, if the electron left our hydrogen atom…
Then the hydrogen atom would have a positive charge
because of the single proton remaining.
So our hydrogen atom would become an ion and be written: H+
Ions
• A neutral atom that loses or gains electrons is
called an ion.
• Ions are particles with an overall positive or
negative charge.
• Let’s try a few more!
Atomic Model Reminders
3
Li
6.941
3p+
4n0
2e- 1e-
+
Li
Let’s say an electron was to leave this atom of lithium…
How many positive charges would you have?
How many negative charges would you have?
What is the total charge on the ion? How would you write the new
symbol?
Atomic Model Reminders
12
Mg
24.3050
12p+
12n0
2e- 8e- 2e-
2+
Mg
Let’s say two electrons were to leave this atom of magnesium…
How many positive charges would you have?
How many negative charges would you have?
What is the total charge on the ion? How would you write the new
symbol?
Atomic Model Reminders
9
F
18.9984
9p+
10n0
2e- 7e
8e-
F
Let’s say an electron was to be added to this atom of fluorine…
How many positive charges would you have?
How many negative charges would you have?
What is the total charge on the ion? How would you write the new
symbol?
1e-
Why do electrons do this?
• Valence orbital = Outermost orbital
• Atoms are the most stable when they have full
valence energy levels.
• It takes energy to move these electrons from
place to place. So electrons will move in
whatever way is the least costly.
• Electrons will transfer in a direction which
requires the least moves to make complete
valence orbitals.
Atomic Model Reminders
11
Na
22.9898
17
Cl
35.453
11p+
12n0
2e-
8e-
1e-
7e
8e- -
8e-
2e-
17p+
18n0
+
Na Cl
Let’s say an electron was transferred between these two atoms, where
would it go?
Notice how many valence electrons each ion now has.
How many positive charges would each ion have?
How many negative charges would each ion have?
What is the total charge on the ion? How would you write the new
symbol?
Ionic Compounds
• Many compounds are formed from ions.
• Most ions try to have 8 electrons in their
valence shell (except H and He). This is called
the “rule of eight” or “octet rule”
• Ionic compounds stay together because
oppositely charged ions are attracted to each
other.
• When compounds are formed this way, we say
that they have an ionic bond.
Ions in Solution
• When ionic compounds break apart we say
that they “dissociate”.
• Some pairs of ions break apart in a solution.
In a strong acid, nearly all ions separate in
water. While in weak acids, few ions break
apart.
How do you know?
• When an element is likely to give up or
capture electrons, we say that it is “reactive”.
• Reactive elements are generally the most
dangerous, because they are looking to
exchange electrons, which is usually
associated with forming new compounds and
often releasing energy!
Uses of Ions
• Although ionic compounds serve a variety of
uses, one of the most useful is the storage and
transfer of electrical energy.
• Ions in solution carry electrical charge in
water.
• Ions are also used to store electricity in most
batteries.