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CHEMISTRY UNIT 3…read more

Slide 2

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Development of the periodic
table…read more

Slide 3

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The early periodic table
During the 19th century scientists tried to find ways to classify elements based on
their properties and atomic weights.
Some elements Scientist
law of octaves, Mistakes
Newlands every eighth assumed all
not similar at all
and put two
ridiculed his
ideas and they
element seemed elements had
1864 similar. been discovered
elements in the
same place
were not
`father of the
Arranged them
Left gaps for modern periodic
in a periodic
Mendelee Placed them in a
table in order of
pattern so their
elements and
v 1869 atomic masses.
properties could
predicted their
matched his
be seen
predictions…read more

Slide 4

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The modern periodic table
Scientists discovered protons and electrons at the start of the 20th century and
they soon developed models of the arrangement of electrons in atoms. The
elements were arranged in order of their proton numbers rather than their atomic
Groups of elements have similar chemical properties as they have the same
number of electrons in their outer shells.
Metals become more reactive as you go down the group and non-metals
become more reactive as you go up the group.
Going down a group there are more occupied energy levels ­ shells ­ so the
atoms get larger. As they get larger the outer electrons are less strongly
attracted to the nucleus. This increased distance and increased shielding means
the outer electrons are less attracted to the nucleus.…read more

Slide 5

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Group 1 ­ the alkali metals…read more

Slide 6

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Group 7 ­ the halogens…read more

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