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Chemical Properties Of The Groups

5.2 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 5.3

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Figure 5.3: 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 metals are very reactive groups.

  • The noble gases are inert (unreactive).

The following diagram illustrates some of the key trends in the groups of the periodic table:

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Figure 5.4: Trends in the groups on the periodic table.

Table 5.2 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 5.2 to predict the chemical properties of unfamiliar elements. For example, given the element Francium () we can say that its electronic structure will be , it will have a lower first ionisation energy than caesium ().

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

Electron structure

Group 1 chlorides

Group 1 elements all form halogen compounds in a 1:1 ratio

Group 1 oxides

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 5.2: Summary of the trends in group 1

Exercise 5.2 See solutions

Use Table 5.2 and Figure 5.4 to help you produce similar tables for group 2 and group 17.

The following two elements are given. Compare these elements in terms of the following properties. Explain the differences in each case. and .

  1. Size of the atom (atomic radius)

  2. Pottassium has 19 electrons. So we get: 91c91552ecfebbe499fbf2eba9f7a6c0.png

  3. Sulfur has 14 electrons so we get: 371810cedac07e4ce92b06529a787d26.png

  4. Neon has 10 electrons so we get: 54e35af6e28049073e906deb1b266658.png

  5. Nitrogen has 7 electrons so we get: c70ff35ddc3adb6d0e6399c86f10abc2.png

Use the Aufbau diagrams you drew to help you complete the following table:

Element No. of energy levels No. of electrons No. of valence electrons Electron configuration (standard notation)

The energy levels are given by the numeral above the boxes, so 1, 2, 3 etc. The number of core electrons is all the electrons that are not in the outermost energy level. The number of valence electrons is the number of electrons in the outermost energy level. And the electron configuration is simply listing the energy levels together with the orbitals and the number of electrons in each orbital. So for magnesium the number of energy levels is 3, the number of core electrons is 10, the number of valence electrons is 2 and the electron configuration is: . Filling in the table gives:

Element No. of energy levels No. of electrons No. of valence electrons Electron configuration (standard notation)

Rank the elements used above in order of increasing reactivity. Give reasons for the order you give.

The order of reactivity is complex and difficult. But it could possibly go like:

See solutions