chemistry ppe Flashcards
what happens in fractional distillation
- vapours rise through column hot at bottom cool at top
- condense when they reach part of column that is below temperature of boiling point
- liquid led away from column
how many spots does a pure substance produce on the chromatogram
1 spot
how many spots does an impure substance produce on the chromatogram
two or more
two ways of knowing if substances are likely to be the same in chromotography
- produce same number of spots that match in colour
- spots travel same distance up paper
when did John Dalton publish his ideas about atoms
1803
what did John Dalton say
all matter was made of tiny particles called atoms, imagined as tiny spheres that couldn’t
when did JJ Thomson publish his ideas about atoms
1897
what did JJ Thompson say
- carried out experiments and discovered electron
- led to him suggesting plum pudding model of atom (ball of positive charge with negative electrons embedded)
when did Ernest Rutherford publish his ideas about atoms
1909
what did Ernest Rutherford say
- wanted to test plum pudding model
- positively charged alpha particles fired at thin gold foil
- most went straight through, but few scattered in different directions
what did Niels Bohr say
-sugge
sted that electrons orbit nucleus in shells
-shells are specific distance from the nucleus
when did James Chadwick publish his ideas about atoms
1932
what did James Chadwick say
found evidence for particles in nucleus but with no charge called neutrons
ratio of a nucleus to an atom
1:10,000
what are isotopes
atoms with different numbers of neutrons
