The history of the periodic table. Ava Campbell.

How was the periodic table formed?

The first element that was discovered was Phosphorus in 1649. It was discovered by Hennig Brand by mistake. Brand discovered prosperous by boiling urine until it split into its base components. He isolated the phosphorous gas and solidified it.

Over the next 200 years, many different chemists discovered a further 63 elements. The collection of elements kept growing and chemists began to see some patterns in the elements properties. This is when the idea of the periodic table was formed.

Johann Dobereiner

The first grouping of elements came from Johann Dobereiner. Between 1817 and 1829 he placed elements in groups of three. This was called the 'Law of Triads'. The elements were grouped together if they had the same properties as other elements. The first triad he created consisted of strontium, calcium and barium. Other triads that he grouped together were the Halogen triad: chlorine, bromine and iodine and the Alkali metal triad: lithium, sodium and potassium. However other scientists were beginning to find groups of 4 and 5 elements with similar properties.

John Newlands

In 1864 John Newlands put forward his 'law of octaves'. He arranged all known elements into a table in order of relative atomic mass. When he did this he realised that each element had similar properties to the element eight places ahead of it. He placed the similar elements into vertical columns.

Newland's table did show a repeating pattern of properties but as he was arranging the elements by atomic mass he had to place some elements into groups that didn't have any matching chemical properties. One example of this is he put iron (a metal) into the same group as oxygen and sulphur which are both non metals. This meant his table was not accepted by other scientists.

Newland's law of octaves.
Dmitri Mendeleev

Dmitri Mendeleev's periodic table was similar to Newlands. Mendeleev published his periodic table in 1869. He arranged the elements that were known into order of relative atomic mass, as Newlands did. Mendeleev also realised that the properties of the elements were related to the atomic mass. The table was arranged so that elements with similar properties fell into vertical columns.

However, unlike Newland, Mendeleevs table had gaps where he put no element. He left these gaps as he believed the elements that went there hadn't been discovered. He also predicted the atomic mass and some properties of the missing elements, which were proved to be true when the elements were discovered.

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