5 marks b When gold foil is bombarded by alpha particles it is found that most of the particles pass through the foil without significant change of direction or loss of energy A few particles are deviated from their original direction by more than 90 Explain in terms of the nuclear model ID: 227193
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Slide1
Q1.
(a) Describe the principal features of the nuclear model of the atom suggested by Rutherford.
(5 marks)
(b) When gold foil is bombarded by alpha particles it is found that most of the particles pass through the foil without significant change of direction or loss of energy. A few particles are deviated from their original direction by more than 90°. Explain, in terms of the nuclear model of the atom and by considering the nature of the forces acting,
(i) why some alpha particles are deflected through large angles,
(ii) why most of the alpha particles pass through the foil without any significant change in direction.
(5 marks)
(Total 10 marksSlide2
Q1.
(a) Describe the principal features of the nuclear model of the atom suggested by Rutherford.
nucleus is small
nucleus is massive
Massive does not mean 'big' in this case - it mean it contains most of the mass
nucleus is positive
electrons surround the nucleus
electrons are negative (or electrons have small mass)
(5 marks)Slide3
(b) When gold foil is bombarded by alpha particles it is found that most of the particles pass through the foil without significant change of direction or loss of energy. A few particles are deviated from their original direction by more than 90°. Explain, in terms of the nuclear model of the atom and by considering the nature of the forces acting,
(i) why some alpha particles are deflected through large angles,
Some alpha particles approach the (gold) nucleus so that their path takes them very near to it. The gold nucleus and alpha particle are both positively charged therefor ethere is a repulsive force between the (gold) nucleus and the alpha particle. This causes the alpha particle to be deflected througha large angle.
(ii) why most of the alpha particles pass through the foil without any significant change in direction.
The space between neighbouring (gold) nuclei is very large large [or the atom is mostly empty space]. The coulomb repulsion depends on an inverse square relationship, therefore the further apart the alpha particle and gold nucleus are, the smaller the repulsive force they will experience, and the less affected the path of the alpha particle wil be.Therefore most alpha particles do not approach nuclei close enough to be (significantly) deflected Slide4
Q2.
In an experiment to investigate the structure of the atom, alpha particles were aimed at thin gold foil in a vacuum. A detector was used to determine the number of alpha particles deflected through different angles.
(a)
(i) In which direction will the number of a particles per second be a maximum?
(ii) State what this result suggests about the structure of the atoms in the metal.
(2 marks)
(b) A small number of alpha particles are scattered through 180°. Explain what this suggests about the structure of the atoms in the metal.
(3 marks)
(c) The figure shows the path of an alpha particle passing near a nucleus.
(i) Name the force that is responsible for the deflection of the alpha particle.
(ii) Draw an arrow on the diagram in the direction of the force on the alpha particle in the position where the force is a maximum.
(iii) The nucleus is replaced with one which has a larger mass number and a smaller proton number. Draw on the diagram the path of an alpha particle that starts with the same velocity and position as that of the alpha particle drawn.
(3 marks)
(Total 8 marks)Slide5
Q2.
In an experiment to investigate the structure of the atom, alpha particles were aimed at thin gold foil in a vacuum. A detector was used to determine the number of alpha particles deflected through different angles.
(a)
(i) In which direction will the number of a particles per second be a maximum?
Straight on (or deflection of zero degrees)
(ii) State what this result suggests about the structure of the atoms in the metal.
The atom consists mainly of empty space [or the volume of the nucleus is (very much) smaller than volume of the atom] Slide6
(b) A small number of alpha particles are scattered through 180°. Explain what this suggests about the structure of the atoms in the metal.
It suggests that
most of the
mass
of an atom is contained in its nucleus [or the mass of the nucleus is greater than the mass of the alpha particle]
the nucleus contains a positive
charge
the
charge
is concentrated at the nucleus Slide7
(c) The figure shows the path of an alpha particle passing near a nucleus.
(i) Name the force that is responsible for the deflection of the alpha particle.
The electrostatic force
or
electromagnetic force
or
coulomb force
(ii) Draw an arrow on the diagram in the direction of the force on the alpha particle in the position where the force is a maximum.
See diagram
- arrow pointing away from the nucleus at the closest distance to the nucleus
(iii) The nucleus is replaced with one which has a larger mass number and a smaller proton number. Draw on the diagram the path of an alpha particle that starts with the same velocity and position as that of the alpha particle drawn.
The repulsion is not due to the mass, but to the electrostatic repulsion between the protons in the alpha particle and nucleus. Therefore there will be less repulsion.
See diagram
- path showing less deflection at all times Slide8