- Contains all known elements.
- Elements are arranged in order of increasing atomic number, number of protons.
- Elements are arranged in groups (vertical columns) which contain elements with similar properties.
- The periodic table today is a product of over 150 years of scientific work.
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John Dalton 1812-1814
- First attempt to order elements
- Problems - at his time -few were known by scientists
- Some of his elements were in fact compound.
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John Newlands 1863
- More elements had been found
- Proposed the law of octaves
- Every 8th element had similar properties and was placed in the same group
- Problems - sometimes more than one element for each space, move elements around to force fit them into his system.
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Dimitri Mendeleyev (1869)
- g-d father of modern periodic table
- Reshuffled Newlands work to order elements in increasing atomic mass
- Created new groups still with similar properties
- Left groups for elements that had not yet been discovered - gave detailed predictions about their chemical properties
- Problems - elements arranged in order of atomic mass not atomic number.
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Modern periodic table
- Elements are ordered in ascending atomic number
- No gaps
- Noble gasses
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