Contributions to Chemistry

Contributions to Chemistry

Four element theory: earth, air, fire & water

Antoine Lavoisier

~1770-1789

Wrote the first extensive list of elements containing 33 elements.

Distinguished between metals and non-metals.

Some of Lavoisier's elements were later shown to be compounds and

mixtures.

Jöns Jakob Berzelius

1828

Developed a table of atomic weights.

Introduced letters to symbolize elements.

Johann Döbereiner

1829

Developed 'triads', groups of 3 elements with similar properties.

Lithium, sodium & potassium formed a triad.

Calcium, strontium & barium formed a triad.

Chlorine, bromine & iodine formed a triad.

First to think that there may be ‘groups’.

John Newlands

1864

The known elements (>60) were arranged in order of atomic weights and

observed similarities between the first and ninth elements, the second

and tenth elements etc. He proposed the 'Law of Octaves'.

Newlands' Law of Octaves identified many similarities amongst the

elements, but also required similarities where none existed. He did

not leave spaces for elements as yet undiscovered.

First to think that there may be ‘periods’.

Lothar Meyer

1869

Compiled a Periodic Table of 56 elements based on the periodicity of

properties such as molar volume when arranged in order of atomic

weight.

Meyer & Mendeleev produced their Periodic Tables simultaneously.

Dmitri Mendeleev

1869

Produced a table based on atomic weights but arranged 'periodically'

with elements with similar properties under each other. Gaps were left

for elements that were unknown at that time and their properties

predicted (the elements were gallium, scandium and germanium). The

order of elements was re-arranged if their properties dictated it, eg,

tellerium is heavier than iodine but comes before it in the Periodic

Table.

Mendeleev's Periodic Table was important because it enabled the

properties of elements to be predicted by means of the 'periodic law':