Chemistry Year 9 (all)

HISTORY OF THE ATOM

DEMOCRITUS born 460BC.

• put forward the idea of atoms.
• thought they were smallest possible particles and everything was made of them.
• stuck together in different patterns.

JOHN DALTON born 1766.

• thought atoms couldn't be broken apart.
• they join together to make e v e r y t h i n g.
• suggested atom of one element plus others of other elements could make compounds.

JJ THOMPSON born 1856.

• thought there was something smaller than atoms.
• discovered the electron.
• created the plum pudding model:

a positive sphere containing equally spaced electrons, with an overall neutral charge. RUTHERFORD born 1871.

• worked with JJ but broke off.
• built on plum pudding model to show most of an atom is empty space.
• his model was confirmed by the gold-leaf experiment, 1905.
• won a Chem Nobel prize in 1908.

CHADWIDE born 1885.

• worked with Rutherford.
• discovered the neutron.
• explained how the same element can have a different mass - isotopes!

BOHR born 1885.

• worked with Rutherford.
• published paper in 1913 saying that electrons don't move randomly, they fit into shells.

ADDITION POLYMERISATION

ADDITION POLYMERISATION reaction that turns monomers into a polymer. Slightly alters the monomers' bonds.

MONOMERS small molecules that make up polymers.

POLYMERS very large molecules made of joined-up smaller molecules.

TYPES OF CHAINS

1. HDPE - high density polyethene. harder to melt. dense, rigid. strong forces of attraction. lines up chains. eg plastic bins.
2. LDPE - low density polyethene. easier to melt. soft, light. weak forces of attraction. branching chains. eg bin bags.

TYPES OF PLASTICS

1. thermosetting - high melting point. can only mold it once. don't melt, burn because bonds are so strong they don't break and instead react with oxygen by burning. strong covalent bonds. polymer chains. don't bend or stretch. eg  worktop…