Atomic structure - development of the atom

Question 1

summarise the plum pudding model

Answer 1

• JJ Thomson proposed that the atom was a positively charged ball will negatively charged electrons embedded in it

Question 2

why was the plum pudding model consistent with the evidence available at the time

Answer 2

• solids cannot be squashed, therefore the atoms which make them up must be solid throughout
• rubbing two solids together often results in static charge so there must be something (electrons) on the outsides of atoms which can be transferred as atoms collide

Question 3

summarise the alpha particle experiment and its conclusions

Answer 3

• Ernest Rutherford and his two students shot alpha particles through a gold sheet suspended in a vacuum to prove the plum pudding model
  From this experiment, they came to these conclusions:
  1. since most of the particles passed straight through the gold foil, it was clear that the atom was made up mostly of empty space
  2. Since a small number of alpha particles were deflected at large angles, it was suggested that there is a concentration of positive charge in the atom, as like charges repel (alpha particle is positive)
  3. the very small number of alpha particles coming straight back suggested that the positive charge and mass are concentrated in a tiny volume in the atom (the nucleus

Question 4

why was a vacuum used in the alpha particle experiment

Answer 4

because it would ensure that any deflection with the alpha particles would be due to collisions with the gold foil and not collisions of anything else

Question 5

what did Neils Bohr suggest in 1913

Answer 5

that electrons orbited the nucleus in different energy levels or at specific distances from the nucleus.

Question 6

who discovered the neutron

Answer 6

james chadwick

Question 7

what are the relative masses of protons neutrons and electrons

Answer 7

protons : 1
neutrons : 1
electrons : 0

Question 8

what are the relative charges of protons neutrons and electrons

Answer 8

protons : +1
neutrons : 0
electrons : -1

Question 9

what is the radius of an atom

Answer 9

1x10^-10

Question 10

what could happen if an atom absorbs electromagnet radiation

Answer 10

it could move from a lower energy level to a higher one

Question 11

what happens if an electron EMITS electromagnetic radiation

Answer 11

it goes from a higher to lower energy level

Question 12

what are ions

Answer 12

a particle with an overall charge

Question 13

what did ancient greeks think atoms were

Answer 13

tiny spheres that couldnt be divided

Question 14

when were electrons discovered

Answer 14

1897

Question 15

why was the discovery of electrons so significant

Answer 15

showed that atoms are not spheres that cannot be divided, rather they have an internal structure

Question 16

why was gold used for the alpha particle experiment

Answer 16

because we can hammer gold out into very thin foil, a few atoms thick