2.2 — models of atomic structure Flashcards
what did john dalton propose as the atomic model?
indivisible, solid spheres, with each element being made up of different types of spheres.
when did dalton propose his atomic model?
early 19th century
what did jj thomson prove, and what did he propose as the atomic model?
thomson proved that atoms were divisible and proposed the ‘plum pudding’ model, which depicted atoms as positively charged with negative electrons embedded throughout.
when did thomson propose his atom model?
1897
who conducted the gold foil experiment?
ernest rutherford, and his students hans geiger and ernest marsden
what did the gold foil experiment involve and how did it’s results contrast what would be expected to occur if thomson’s model was accurate?
the gold foil experiment involved firing (positive) alpha particles at a thin gold foil inside a vacuum. if thomson’s model was correct, the positive ‘pudding’ would repel most of the particles. however, this did not happen, and most alpha particles passed straight through, with a few deflecting at large angles or even bounding back.
what were rutherford’s conclusions after conducting the gold foil experiment? (3 points)
the fact that most of the alpha particles passed through the gold foil undeflected indicated that atoms are mostly empty space.
the small number of particles that deflected at large angles or bounced back suggested the presence of a tiny, dense, positively charged nucleus at the centre of the atom, with the alpha particles deflecting being due to electrostatic repulsion.
since the atom was mostly empty space with a dense nucleus, rutherford proposed that negative electrons must orbit the nucleus in a ‘cloud’ to maintain the atom’s overall neutrality.
what model of the atom was proposed after the gold foil experiment?
the nuclear model
what were the discoveries found after rutherford’s initial nuclear model? (2)
the discovery of the proton and the neutron
how was the proton discovered?
research by henry moseley showed that nuclear charge increases by one unit from one element to the next, leading to rutherford being able to identify positively charged particles in the nucleus, protons
how was the nucleus discovered?
it was a mystery as to why atomic nuclei were heavier than they should be if they only contained protons. after speculation from rutherford about another type of nuclear particle, james chadwick discovered the neutron, which then provided the mass needed to account for the discrepancy in the nucleus’ weight
what was the flaw in rutherford’s model?
the inability to explain why electrons, attracted to the nucleus, wouldn’t simply collapse into it
what was suggested in bohr’s model of the atom? (3)
electrons orbit the nucleus in specific energy levels, or shells, that they can jump between these shells by absorbing or emitting light of particular wavelengths and accounted for the observed spectra of light emoted or absorbed by atoms.
what did experiments reveal that electrons in the same shell possessed and what did this lead to the introduction of?
it revealed different energy levels, and lead to introduction of subshells
