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Ions and Isotopes
Ions - Charged Atoms
 The identity of an element is determined by the number of
in its nucleus.
we change the
o Therefore if we change the number of
 HOWEVER, If we change the number of electrons we do not change the element…
instead, we have simply changed the overall charge
 Atoms can either loose
of the atom.
or gain
electrons.
 Any time an atom becomes charged, we call it an ion
.
o If an atom gains electrons, it becomes a negatively
charged ion. (anion)
o If an atom loses electrons, it becomes a positively
charged ion. (cation)
Test Yourself! Complete the table below:
Number of
protons
Number of
electrons
10
10
0
ALUMINUM
13
10
3+
Y
Al3+
Chlorine
17
18
1-
y
Cl-
Nitrogen
7
9
2-
y
N2-
Element
Neon
Net charge
Ion? symbol
(Y/N
)n
Ne
How Many Electrons Gained or Lost?
 Atoms can become stable with a full valence shell of electrons. (last or outer orbit)
 Therefore, atoms will gain or lose the fewest number electrons possible to achieve a full valence o Metals
tend to lose electrons to become positive ions (cations).
o Non-metals tend to gain electrons to become negative ions (anions).
 Example: Magnesium (Mg) is a metal with 2
valence electrons
To get a full outer shell it can either gain 6
electrons or lose 2
Therefore, it is more likely to lose
electrons and form the cation
Bohr Diagrams for Ions
 Bohr diagrams for ions have two modifications:
1. place square brackets around the whole diagram
2. write the charge in the top right corner, outside the brackets
Practice: On a separate sheet of paper, try drawing the Bohr diagrams for K+,
Be2+, N2-, and FNow try the H+ ion… neat eh?
electrons.
ion.
example: Oxygen Ion (O2-)
Isotopes – Changing the Atomic Mass
Remember: There are 3 sub-atomic particles; protons, electrons and neutrons.
Change the number of protons and you change the element
Change the number of electrons and you create an ion
Question: What happens when you change the number of neutrons?
 Sometimes atoms either gain or lose neutrons.
 Since neutrons have no charge
this does not affect the charge of the atom.
 Neutrons have about the same mass
as protons, so a change in the number of
neutrons results in a change in the overall mass of the atom
.
 Any time an atom has a different mass than is listed on the periodic table, we call it an
isotope
Example:
. This means it has gained or lost neutrons
24
a) 12
26
b) 12
Mg
Mg
p =12
p = 12
e =12
e =12
n =12
n =14
.
12
M
Magnesium
a periodic
These two atoms of Mg have the same number of electrons and protons
, but a different number of neutrons
. Which one is the isotope? Mg 24
.
Practice – Use your periodic table to help complete the table below
Name of Element
Copper
Oxygen
Calcium
Symbol

Cu
29
62
Atomic
Number
29
8
20
Relative
Atomic
Mass
Number
of
Protons
Number
of
Neutrons
Number
of
Electrons
Net
Charge
63.5
29
33
28
+1
8
7
8
15
41
20
35
35
80
(Y/N)
Isotope
(Y/N)
Y
Y
n
Y
Y
Y
Y
n
0
21
Bromine
Ion?
18
45
+2
-1
36