At

Question 1

John Dalton

Answer 1

1803

atoms are spheres, each element made from different spheres

Question 2

j.j. thomson

Answer 2

1897
discovered the electron. plum pudding model developed. the atom is not solid, is made up of other particles.

Question 3

ernest rutherford

Answer 3

1909
discovered the nucleus & that it was very small & + charged. concluded the atom was mainly empty space and made up a negative cloud.
gold leaf experiment.

Question 4

gold leaf experiment

Answer 4

positive alpha particles fired at thin gold leaf. most passed through - atoms mostly empty. some deflected - hit small + nucleus. few straight back - tiny.

Question 5

niels bohr

Answer 5

faulted rutherfords model - cloud of electrons would collapse as +- attraction. electrons are in fixed energy shells.

proof - when EM radiation absorbed electrons move between energy shells. they emit this radiation when e- move down to lower energy shells.

Question 6

relative atomic mass, Ar

Answer 6

WEIGHTED MEAN MASS of an atom of an element, compared with 1/12th of the mass of an atom of CARBON-12

Question 6

Relative Isotopic Mass

Answer 6

mass of an atom of an isotope compared to 1/12th of the mass of an atom of CARBON-12

Question 7

Relative Molecular Mass, Mr

Answer 7

mean mass of a molecule compared to 1/12th of the mass of an atom of CARBON-12

Question 8

Mass spectra

Answer 8

m/z = mass/charge ratio
through mass spectrometer atoms usually lose 1e- to form +1 ion, so m/z value is m/1 mostly, hence Mr