Models of the atom

Question 1

Why has the model of the atom changed over time?

Answer 1

new evidence of its structure has become available from new experiments as technology has developed

Question 2

plum pudding model (3)

Answer 2

• J.J.Thomson’s model
• the atom has negatively charged electrons embedded in a uniform pattern in a positive ball
• the model showed that both positive and negative charges existed, and accounted for the atom being neutral

Question 3

Rutherford’s model/solar system model (2)

Answer 3

• atom contains a very small, positively charged nucleus which electrons orbit (like planets orbiting the sun)
• it was proved to be correct by other scientists who fired alpha particles at gold film

Question 4

the atomic model/Bohr model (2)

Answer 4

• electrons orbit a positive nucleus in well defined energy levels/orbits
• electrons can move between energy levels if they lose or gain energy

Question 5

Which model of the atom is being described?

a) the atom is mostly empty space and has a positive nucleus which contains most of the mass of the atom [1]
b) electrons can only orbit the atom in certain energy levels or orbits [1]
c) the atom is neutral with negative electrons embedded in a positive ball [1]

Answer 5

a) Rutherford’s model/solar system
b) Bohr model/atomic
c) plum pudding model/Thomson

Question 6

Describe the three models of the atom [3]

Answer 6

plum pudding model: negative electrons/plums in a positive ball/dough

rutherford: small positive nucleus compared to overall atomic diameter
bohr: electrons orbiting a positive nucleus in definite, discrete energy levels

Question 7

Explain how Rutherford’s work led to the conclusion that the atom has a small, positive nucleus [4]

Answer 7

positive alpha particles were fired at nucleus

most went through undeflected, so most of the atom must be empty space

there is a small nucleus as only a very few alpha particles bounced back

Question 8

Suggest how the Bohr model allows astronomers to determine which gases are present in the outer surfaces of stars [4]

Answer 8

in the bohr model electrons orbit the nucleus in very definite, discrete energy levels

these energy levels are the same values for atoms of a given element

electronic transitions between energy levels in atoms of a gas lead to certain frequencies of an electromagnetic radiation being emitted or absorbed in the spectra of light from stars

the characteristic lines identify atoms of a particular element