Imagine your work seems like a confusing mess – and then suddenly it all makes sense! That’s how many chemists felt, when the periodic table was first published over 130 years ago.
The periodic table is the chemists’ map. It helps you understand the patterns in chemistry. Today we take it for granted. But it took hundreds of years, and the work of hundreds of chemists, to develop.
First, find the elements!
The first job was to find out which substances were elements. Not easy. Plato and Aristotle thought earth, air, fire and water were the only elements. The alchemists opted for mercury, Sulphur and salt.
In fact, many elements were already in use – for example gold, silver, lead and copper - but they were not classed as elements. Then in 1661, Robert Boyle came up with the definition we still use: an element is any substance that cannot be broken down into simpler substances. The show was on the road.
Over the next two hundred years, over 50 elements were discovered. Scientists began to notice patterns in their behaviour, and try to explain them.
The Periodic Table
Dmitri Ivanovich Mendeleev was born in Siberia in 1834, the youngest of 17 children. By the time he was 32 he was a Professor of Chemistry.
Mendeleev collected a huge amount of data about the elements, some by research, and some by writing to scientists around the world. He made a card for each of the known elements (by then 63), with all the data written on.
He arranged the cards on a table, first in order of increasing atomic weight, then into groups with similar behaviour, resulting in the periodic table, published in 1869.
Mendeleev’s table was a big improvement on Newland’s. He ironed out the inconsistencies by leaving gaps for elements not yet discovered.
He named three of them eka-aluminium, eka-boron and eka-silicon, predicted their properties. Soon gallium, scandium and germanium were discovered. They fitted his predictions – and at last scientists accepted the idea of periodicity.
His table became the blueprint for our modern one.
DMITRI IVANOVICH MENDELEV
RUSSIAN
1834-1907
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