# 2.1 Chemical periodicity

The chemistry of the elements is extremely varied. But amidst this variety there are patterns, and the best known and most useful is chemical periodicity: if the elements are laid out in order of atomic number, similar elements occur at regular intervals.

So who first spotted these relationships?

A number of scientists could claim a share of the credit, but the name you’ll most often hear in this regard is Dmitri Mendeleev, the nineteenth century Russian chemist. His ground breaking work led to the construction of the periodic table as we know it today.

Essentially the periodic table is a graphic representation of the patterns in the physical and chemical behaviour of the elements. In fact there are various versions, one of which is shown in Figure 14.

Figure 14 The periodic table

Looking closely at Figure 14 you can see the elements are listed by their atomic numbers, shown here above each symbol. They are arranged in horizontal rows called periods and vertical columns called groups.

The table can also be neatly divided up into blocks of elements, again this is shown in Figure 14 where the transition elements, lanthanoides, actinoides and typical elements are highlighted in different colours.

Chemical periodicity is apparent from the appearance of similar elements in the same group, which are often given specific names. For example, the alkali metals appear in the first column on the left of the Table, and the noble gases in the last column on the right.

To illustrate this point further you will look in more detail at these particular groups in the next section.

OpenLearn - Discovering chemistry
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