Chemistry, Models of atomic structure...

what is the relative mass of an electron?

models of atomic [blank_start]structure[blank_end] have changed slightly over the years... in the start of the [blank_start]19th[blank_end] century, [blank_start]john Dalton[blank_end] described atoms as [blank_start]solid spheres[blank_end]... he said that these [blank_start]spheres[blank_end] made up different elements. in [blank_start]1897[blank_end], [blank_start]J.J.Thompson[blank_end] discovered the [blank_start]electron[blank_end]. this showed that atoms couldn't be solid spheres and indivisible. the new model was known as the [blank_start]plum pudding model[blank_end]. in [blank_start]1909[blank_end], [blank_start]Ernest Rutherford[blank_end] and his students conducted the [blank_start]gold foil experiment[blank_end] where they fired [blank_start]alpha[blank_end] particles at a very thin [blank_start]gold[blank_end] sheet. the plum pudding model suggested that [blank_start]most[blank_end] alpha particles would be slightly [blank_start]deflected,[blank_end] however most particles passed straight through with only a few being deflected. this showed that the plum pudding model was [blank_start]wrong[blank_end]. [blank_start]Rutherford[blank_end] developed the [blank_start]nuclear model[blank_end]. this showed a tiny [blank_start]positive[blank_end] nucleus, surrounded by a [blank_start]cloud[blank_end] of negative electrons, with most being [blank_start]empty space[blank_end]. scientists realised that if electrons where in a cloud then they would [blank_start]spiral[blank_end] down and cause the atom to [blank_start]collapse[blank_end]. [blank_start]Niels Bohr[blank_end] proposed a new model where electrons exist in shells or orbits of [blank_start]fixed energy[blank_end]. when electrons move between shells, [blank_start]electromagnetic radiation[blank_end] is absorbed or emitted. this model fitted experimental observations. this model is still used even though we can refine it into [blank_start]sub-shells[blank_end] as this model is simple and easy to understand.

who described electrons as solid spheres and in when? [blank_start]John Dalton[blank_end] and in [blank_start]the 19th centrury[blank_end].

in 1892, jj. Thompson made the plum pudding model.

put the scientists in order with their year and experiment... [blank_start]John Dalton[blank_end] [blank_start]described atoms as solid spheres[blank_end] in [blank_start]the 19th century[blank_end]. [blank_start]ernest Rutherford[blank_end] [blank_start]conducted the gold foil experiment[blank_end] in [blank_start]1897.[blank_end] [blank_start]Niels bohr[blank_end] [blank_start]discovered shells and orbits[blank_end] of [blank_start]fixed energy[blank_end]. scientists later refined this to have [blank_start]sub-shells[blank_end].