More Periodic Table Trends Page 2
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Name: ______________________
Ionization Energy
ionization energy: energy required to remove the most loosely held electron from an atom
Thought POE: How does ionization energy vary within groups and periods?
Trend Down
P
O
E
As you go down, there are more shells, therefore
a Group
Less
the last electron is farther away from the nucleus
energy
and it is not held as tightly with the nucleus;
therefore it is easier to remove
Trend Across
P
O
E
There are more protons so the electrons are closer
a Period
More
to the nucleus and held more tightly; therefore it
energy
is harder to remove them
The energy required to remove the first electron from an atom is called the ‘first ionization energy’ (or
simply the ‘ionization energy’). The successive ionization energies are the energies required to remove
electrons beyond the first electron.
Li Li
+
-
st
+ e
1
ionization energy = 521 kJ
Li
+
2+
-
nd
Li
+ e
2
ionization energy = 7304 kJ
Li
2+
3+
-
rd
Li
+ e
3
ionization energy = 11 752 kJ
As you might predict, ionization energy increases with the removal of each additional electron. Examine
the following chart to identify any further trends in ionization energies.
Successive Ionization Energies of Period 3 Elements
Element
First
Second
Third
Fourth
Fifth
Sixth
Seventh
Na
496
4560
Mg
738
1450
7730
Al
577
1816
2744
11600
Si
786
1577
3228
4354
16100
P
1060
1890
2905
4950
6270
21200
S
999
2260
3375
4565
6950
8490
27000
Cl
1256
2296
3850
5160
6560
9360
11000
Ar
1520
2665
3945
5770
7230
8780
12000
For each element you can find one very large increase between a different pair of ionization energies. For
sodium, this large increase is between the first and second ionization energies. For magnesium, the large
increase is between the second and third ionization energies. Where is the large increase for aluminum?
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