Chemical properties of the groups
In some groups, the elements display very similar chemical properties and some of the
groups are even given special names to identify them. The characteristics of each group are
mostly determined by the electron configuration of the atoms of the elements in the group.
The names of the groups are summarised in Figure 1
Figure 1: Groups on the periodic table
A few points to note about the groups are:

Although hydrogen appears in group 1, it is not an alkali metal.

Group 15 elements are sometimes called the pnictogens.

Group 16 elements are sometimes known as the chalcogens.

The halogens and the alkali earth metals are very reactive groups.

The noble gases are inert (unreactive).
Groups in the periodic table
The following diagram illustrates some of the key trends in the groups of the periodic table:
Figure 2: Trends in the groups on the periodic table.
Table 3 summarises the patterns or trends in the properties of the elements in group 1.
Similar trends are observed for the elements in the other groups of the periodic table. We
can use the information in Table 3 to predict the chemical properties of unfamiliar elements.
For example, given the element Francium (Fr) we can say that its electronic structure will
be [Rn]7s1, it will have a lower first ionisation energy than caesium (Cs).
One general trend that is not shown is the melting and boiling points. For the metals (groups
1 to 13) the melting and boiling points increase as you go up the group. For the non-metals
the melting and boling points decrease as you go up the group.
You should also recall from chapter Chapter 2 that the metals are found on the left of the
periodic table, non-metals are on the right and metalloids are found on the zig-zag line that
starts at boron.
Element
73Li
73Na
73K
73Rb
73Cs
Electron structure
[He]2s1
[Ne]3s1
[Ar]4s1
[Kr]4s1
[Xe]5s1
Group 1 chlorides
LiCl
NaCl
KCl
RbCl
CsCl
Group 1 elements all form halogen compounds in a 1:1 ratio
Group 1 oxides
Li2O
Na2O
K2O
Rb2O
Group 1 elements all form oxides in a 2:1 ratio
Atomic radius
Increases as you move down the group.
First ionisation energy
Decreases as you move down the group.
Electronegativity
Decreases as you move down the group.
Melting and boiling point
Decreases as you move down the group.
Density
Increases as you move down the group.
Table 1: Summary of the trends in group 1
Exercise 1: Groups in the periodic table
Problem 1:
Use Table 3 and Figure 2 to help you produce similar tables for group 2 and group 17.
Practise more questions like this
Answer 1:
1)
Cs2O
Element
Be
Mg
Ca
Sr
Ba
Electron structure
[He]2s2
[Ne]3s2
[Ar]4s2
[Kr]5s2
[Xe]6s2
Chlorides
BeCl2
MgCl2
CaCl2
SrCl2
BaCl2
SrO
BaO
All form chlorides in the ratio 1:2
Oxides
BeO
MgO
CaO
All form oxides in the ratio 1:1
Atomic radius
Increases down the group
First ionisation energy
Decreases down the group
Electronegativity
Decreases down the group
Boiling and melting
point
Decreases down the group
Density
Increases down the group
2)
Element
F
Cl
Br
I
At
Electron
configuration
[He]2s22
p5
[Ne]3s23
p5
[Ar]4s24
p5
[Kr]5s25
p5
[Xe]6s26
p5
Atomic radius
Increases down the group
First
ionisation
energy
Decreases down the group
Electronegati
vity
Decreases down the group
Boiling and
melting points
Increases down the group
Density
Increases down the group
Note that the melting and boiling points of the halogens DO NOT follow the trend given.
Problem 2:
The following two elements are given. Compare these elements in terms of the following
properties. Explain the differences in each case. 2412Mg and 4020Ca.
1. Size of the atom (atomic radius)
2. Electronegativity
3. First ionisation energy
4. Boiling point
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Answer 2:
a. Calcium has a larger atomic radius than magnesium. Calcium has more electrons than
magnesium and is filling an extra energy level. This increases the atomic radius.
b. Magnesium has a higher electronegativity than calcium. As you move down a group
the valence electrons are further away from the nucleus and so experience less
attraction from the nucleus. This decreases the elements pull on the electrons
(electronegativity).
c. Magnesium has a higher first ionisation energy than calcium. As you move down a
group, the outermost electrons are further away from the nucleus and are not held as
tightly. This makes the ionisation energy higher for atoms at the top of a group.
d. Magnesium has a higher boiling point than calcium. Magnesium has stronger forces
holding its atoms together and so more energy is needed to make magnesium boil.
Problem 3:
Study the following graph and explain the trend in electronegativity of the group 2 elements.
Practise more questions like this
Answer 3:
As you move down a group the electronegativity decreases. This is due to the valence
electrons being further away from the nucleus and so experience less attractive forces. As
the electrons are not held as tightly the element's electronegativity decreases.
Problem 4:
Refer to the elements listed below:

Lithium (Li)

Chlorine (Cl)

Magnesium (Mg)

Neon (Ne)

Oxygen (O)

Calcium (Ca)

Carbon (C)
Which of the elements listed above:
1. belongs to Group 1
2. is a halogen
3. is a noble gas
4. is an alkali metal
5. has an atomic number of 12
6. has four neutrons in the nucleus of its atoms
7. contains electrons in the 4th energy level
8. has all its energy orbitals full
9. will have chemical properties that are most similar
Practise more questions like this
Answer 4:
1. Lithium
2. Chlorine
3. Neon
4. Lithium (Group 1 metals are known as alkali metals)
5. Carbon
6. Lithium
7. Calcium
8. Neon
9. Magnesium and calcium would have similar chemical properties as they are in the same
group of the periodic table.
Activity 1: Inventing your own periodic table
You are the official chemist for the planet Zog. You have discovered all the same elements
that we have here on Earth, but you don't have a periodic table. The citizens of Zog want to
know how all these elements relate to each other. How would you invent the periodic table?
Think about how you would organise the data that you have and what properties you would
include. Do not simply copy Mendeleev's ideas, be creative and come up with some of your
own. Research other forms of the periodic table and make one that makes sense to you.
Present your ideas to your class.
Circular periodic table
Image from Wikimedia commons