Task 3- Trends in the Periodic Table
1. Complete the table 1 below
Element
Proton Number Z
Li
Na
K
Rb
Cs
First Ionisation
Energy (kJmol-1)
520
496
419
403
376
3
11
19
37
55
2. Plot a graph of first ionisation energy against the proton number, Z.
(2 marks)
First Ionisation Energy
600
500
400
300
First Ionisation Energy
200
100
0
3
11
19
37
55
Figure 1: First Ionisation Energy based on the Proton Number
3. With reference to the graph, as you move down the group does the
ionisation increase or decrease? Include a reason for your answer.
(4 marks)
As shown in the graph, as you move down the group the First Ionisation
Energy decreases. The First Ionisation Energy for Lithium is 520kJmol-1 a
relatively high number in comparison to the other elements. Sodium is
the next element as you go down group 1. The First Ionisation Energy of
Sodium is 496kJmol-1. This is a difference of 24 kJmol-1, showing a
decrease in the First Ionisation Energy. This trend is continued as you go
further down group 1 in the periodic table. Potassium is the next element
down group 1 and it has a First Ionisation Energy of 419 kJmol-1,.a
decrease of 77 kJmol-1.
The decrease in the First Ionisation Energy down a group can be
explained in terms of the distance from the nucleus to the electron being
increased. The further from the nucleus the outermost electron is, the less
attraction there is between the electrons and the nucleus, therefore, the
less energy is required to remove the electron.
The electron shells between the valence shell and the nucleus also
contribute a ‘shielding’ effect. This reduces the attraction between the
valence electrons and the attraction force of the nucleus. Resulting in less
Ionisation Energy being needed to remove the valence electron.
4. Using the internet, find values for the atomic radius of the above
elements. Plot a graph of proton number against atomic radius. You
may plot it on the first graph. (4 marks)
Element
Li
Na
K
Rb
Cs
Proton Number
3
11
19
37
55
Atomic Radius (pm)
145
186
220
248
260
Atomic Radius
300
250
200
150
Atomic Radius
100
50
0
3
11
19
37
55
Figure 2: The Atomic Radius in comparison to the Proton Number
5. Does the atomic radius increase or decrease down the group? (1
mark)
As shown in Figure 2, the atomic radius increases as you go down the
group.
6. Using the above information, describe the reactivity of the elements
down the group, giving examples. You will need to also provide a
chemical equation and describe the observations (6 marks)
The reactivity of the elements increases as you go down a group on the
periodic table.
Electrons are held in their shells by an attractive force from the protons in
the nucleus. Whenever metals react, they do so by losing their valence
electron(s).
The valence electron in lithium (the first element in group 1) is relatively
close to the nucleus and the force holding the electron in place is quite
strong. Therefore, the valence electron is relatively hard to remove which
means that lithium is not as reactive as those further down group 1, for
example, Potassium. Potassium has 4 electron shells and 1 valence
electron. Even though it has the same amount of valence electrons and
lithium, it is more reactive because there is less force attracting the
valence electron to the nucleus due to the ‘shielding’ effect from the
electron shells.
7. Would group 2 show a similar trend to group 1? Find evidence on
the internet to support your answer. (4 marks)
Group 2 would show a similar trend to group 1 as you are still going down
a group on the periodic table that is part of the ‘metals’ section of the
periodic table.
8. Complete Table 2 Below (1 mark)
Element
Proton Number Z
Li
Be
B
C
N
O
F
Ne
3
4
5
6
7
8
9
10
First Ionisation
Energy (kJmol-1)
520
900
801
1806
1402
1314
1681
2081
9. Plot a graph of First Ionisation Energy against the proton number, Z.
(2 marks)
First Ionisation Energy
2500
2000
1500
First Ionisation Energy
1000
500
0
3
4
5
6
7
8
9
10
Figure 3: First Ionisation Energy against the Proton Number
10. With reference to the graph, as you move across the period (left to
right) does the ionisation increase or decrease? Include a reason for
your answer. (4 marks)
As you move across the periods the ionisation energy generally increases.
Moving from one element to the next across a period, an additional proton is
added to the nucleus, which increases the core charge. Therefore, the electrons
in the outermost shell will have a stronger attraction to the nucleus. As a result
of this, it will require more energy to remove an electron from the atoms with
the larger atomic number in a particular period. However, there are a few
exceptions. This includes Boron, which has an unusually low ionisation energy
and Carbon which has an unusually high ionisation energy.
11. Complete table 3 (1 mark)
Element
Proton Number Z
Li
Be
B
C
N
O
F
Ne
3
4
5
6
7
8
9
10
Electronegativity
(Pauling)
0.98
1.57
2.04
2.55
3.04
3.44
3.98
0
12. Plot a graph of the electronegativity against the proton number, Z. (2
Marks)
Electronegativity (pauling)
4.5
4
3.5
3
2.5
Electronegativity
(pauling)
2
1.5
1
0.5
0
3
4
5
6
7
8
9
10
13. With reference to the graph, as you move across the period (left to
right) does the electronegativity increase or decrease? Give a reason
for your answer (4 marks)
As you move across the period the electronegativity increases. The
electronegativity increase as a proton is being added to the nucleus
creating a stronger attraction. As the attraction force of the nucleus
increases, the electrons have a stronger attraction to the nucleus.
Resulting in a larger electronegativity.
14. How would you describe the reactivity across the period? Give a
reason for your answer. (3 marks)
The reactivity decreases as you go across the period. This is because the
ionisation energy increases. The higher the ionisation energy, the harder
it is to remove the valence electrons. For an element to react, it has to lose
its valence electrons. If they are harder to remove, it will have a lower
reactivity.
15. Explain why Neon does not follow the trend? (1 mark)
Neon does not follow the trend because it has a full outermost shell.
Because it has a full outermost shell, it doesn’t need to attract electrons to
it to fill the outermost shell.