Chemistry - history of periodic table & groups

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  • Created by: midget17
  • Created on: 02-04-18 10:25
John Dalton
Published a table of elements 1808 - elements in order of atomic weights
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John Newlands
1864 - arranged elements in order of mass, noticed every eighth element were similar - shared 'law of octaves', however didn't realise that scientists were still discovering elements, - pattern only worked up to a certain point
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Why did scientists reject Newlands' theory?
He didn't leave gaps for undiscovered elements - his pattern only worked up to a certain point, and then failed
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Dmitri Mendeleev
1869 - arranged discovered elements in order of mass, periodically, left gaps for undiscovered elements and predicted what their properties should be - new elements matched with his predictions
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Problem with Mendeleev's table
Not all elements fit e.g. argon, couldn't be ordered by mass and still have the same properties as the others in the group
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How Mendeleev's problem was dealt with
20th century - more knowledge about the structure of the atom, elements in order of their number of protons (atomic number)
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Group number =
Number of electrons in outer shell
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Noble Gases (0)
Eight electrons in outer shell - very stable
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Alkali metals (1)
Very reactive, have to be stored in oil, reactivity increases as you go down the group, low density and soft, silvery surface until cut, low boiling points which get lower as you go down the group
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Alkali metals - reaction with water
Fizzes, forms hydrogen gas and a metal hydroxide - potassium reacts so vigorously it ignites
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Halogens (7)
Low melting points and boiling points, poor conductors
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Other cards in this set

Card 2

Front

John Newlands

Back

1864 - arranged elements in order of mass, noticed every eighth element were similar - shared 'law of octaves', however didn't realise that scientists were still discovering elements, - pattern only worked up to a certain point

Card 3

Front

Why did scientists reject Newlands' theory?

Back

Preview of the front of card 3

Card 4

Front

Dmitri Mendeleev

Back

Preview of the front of card 4

Card 5

Front

Problem with Mendeleev's table

Back

Preview of the front of card 5
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