Notes for Periodic Table.

Development of the periodic table

➢ The elements in the periodic table have been arranged in the order of the number of protons (a.k.a. atomic number)

The next significant stage in the development of the periodic table was discovered by came from John Newlands. He arranged the known elements in order of their atomic masses. He introduced the ‘law of octaves’ which meant that every eighth element had similar properties. As it didn’t work for all the known elements it was therefore dismissed by the scientists.

The most significant develop was introduced by the work of Dmitri Mendeleev. He put the elements in order of the relative atomic mass however he left certain gaps for the undiscovered elements, he was even able to work out the atomic mass for these in discovered elements. ✓ In 1875 when the element gallium was discovered, the properties were found close to Mendeleev’s predictions.
He had also predicted the properties of the unknown elements. Along with ordering the elements he figured out the physical and chemical properties were related to the atomic mass. Therefore knew how to arrange them so each element was put into a group, in vertical columns in his table.

➢ The periodic table gives us specific information about each of the elements, it gives us the symbol of each element (e.g. magnesium=Mg) and the atomic number either at the top or the bottom of the box. ➢ A atom is structured by the subatomic particles which are; ✓ Neutrons ✓ Protons ✓ Electrons
Within the centre of an atom there is a nucleus which is made up of the protons and neutrons. But around the nucleus there is an ‘energy’ shell which is where the electrons are.
(The electrons are always orbiting the nucleus in those shells.)

➢ Here is a table to show the sub-atomics and the properties:

➢ The work of Mendeleev

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