How was the nuclear model of the atom developed by Rutherford in his experiments?
Rutherford's experiment on alpha particle scattering:
1) Parallel beams of ?-particles were directed at a thin piece of gold foil.
2) Most ?-particles went straight through, and some were deflected slightly. However, about 1/20000 ?-particles appeared to
What did Rutherford's experiment on alpha particle scattering confirm?
- The atom is mostly empty space (because most ?-particles were not deflected).
- Most of the mass and all of the positive charge is concentrated in a tiny region at the centre.
- This central nucleus only affected the ?-particles when they came close to
What was the apparatus used in Rutherford's alpha particle scattering experiment?
1) ?-particle source encased in metal with a small aperture - allows a fine beam of ?-particles to emerge.
2) Air in apparatus was pumped out, leaving a vacuum - this is so that ?-particles are not absorbed by the air.
3) Gold as the foil material - gold
In alpha particle scattering, what is the deflection of the alpha particles due to?
The electrostatic repulsion between the positive charge of the ?-particle and the positive charge of the nucleus of the atom.
How would you describe the electrostatic repulsive force of the alpha particle and the gold nucleus?
The electrostatic repulsive force of the ?-particle and the nucleus is equal but opposite to each other. However, it has a much greater effect on the motion of the ?-particle than the gold nucleus.
How is the degree of repulsion affected by how close the alpha particle is to the nucleus?
The closer the path of the ?-particle to the nucleus, the greater the repulsion between them. A head on ?-particle will be back-scattered through 180�.
How can we determine the magnitude of the electrostatic repulsive force F?
Use Coulomb's law.
How would using faster alpha particles affect back scatter?
Their inertia would tend to carry them forward.
What is are the features of the simple atomic model?
� Protons and neutrons make up the nucleus of the atom.
� Electrons move around the nucleus in a cloud - some closer to, and some further from, the centre of the nucleus.
� All matter is mostly empty space.
What is the radius of a proton and a neutron?
10^-15m
What is the radius of a nucleus?
10^-15 to 10^-14m
What is the radius of an atom?
10^-10m
What is the radius of a molecule?
10^-10 to 10^-6m
How do you figure out the mass of one atom if you have Avogadro's constant and the mass of a lump of material?
Mass (the whole material) / Na
How do you figure out the volume of a proton, where its radius is 0.8x10^-15m?
4/3 ?r^3
What is the mass of a proton?
1.67x10^-27kg
How would you figure out the density of a proton, if you have its mass and its volume?
What assumption are you making?
Density = mass/volume
You are making the assumption that there is little empty space between atoms.
What determines what element an atom is?
The number of protons in its nucleus.
What are isotopes?
Isotopes are nuclei of the same element with a different number of neutrons but the same number of protons.
What is the charge Q of an atom?
It is electrically neutral; it has the same number of electrons as it does protons.
How does an atom become an ion?
If it gains or loses an electron - it is no longer electrically neutral.
What determines an atom's nuclear properties?
The number of nucleons it has.
What are the three isotopes of hydrogen?
1) Protium 1�1 H
2) Deuterium 2�1 H
3) Tritium 3�1 H
What is the strong nuclear force?
An attractive force between nucleons. It is what holds the nucleus together.
How does the strong nuclear force act?
It only acts over short distances (10^-14m), only affecting the nucleons around it.
Two protons are adjacent to each other in a nucleus, separated by 2 proton radii (1.6x10^-15m). They repel each other with a charge of 1.6x10^-19C each.
i) How do you figure out the electrostatic repulsive force F?
ii) How do you figure out the attractive
i) F = Qq/4??0r2 = (1.6x10^-19)2/4??0*(1.6x10^-15)^2 ? 90N.
ii) F = GMm/r2 ? 7.3x10^-35N
iii) These forces are not equal to each other. Hence, there must be another attractive force between the protons, with a value of at least 90N when the protons are se
Why do heavy nuclei have more neutrons than protons?
The strong nuclear force has a short range and is not enough at longer distances to stop the protons from repelling each other. The neutrons help separate the protons.
What happens when a nucleus exceeds proton number 83?
When the proton number exceeds 83, adding more neutrons may not be enough. The nuclei may be unstable.
What two families can sub-atomic particles be divided into?
1) Hadrons
2) Leptons
What are hadrons?
Particles affected by the strong nuclear force.
What are some examples of hadrons?
Protons and neutrons.
What are leptons?
Particles that are not affected by the strong nuclear force.
What are some examples of leptons?
Electrons and neutrinos.
What are hadrons made up of?
Fundamental particles called quarks.
What are hadrons held together by?
The strong nuclear force.
What are the six kinds of quark?
1) Up
2) Down
3) Strange
4) Charm
5) Bottom
6) Top
What quarks does a proton comprise of?
Up Up Down
UUD
What quarks does a neutron comprise of?
Up Down Down
UDD
Are neutrons and protons fundamental particles?
No, because they contain charged constituents called quarks.
How are antiquarks represented?
By a bar above the quark letter.
What are antiquarks needed to account for?
The existence of antimatter.
What does quark theory account for and how?
Quark theory accounts for properties of hadrons by identifying the basic properties of quarks - baryon number B, charge Q, and strangeness S.
What is the Q, B, and S of an up quark?
Q = +2/3, B = +1/3, S = 0
What is the Q, B, and S of a down quark?
Q = -1/3, B = +1/3, S = 0
What is the Q, B, and S of a strange quark?
Q = -1/3, B = +1/3, S = -1
What are the Q, B, and S of antiquarks?
Opposite to the quark values.
What is conserved in all hadron interactions?
Q, B, S, charm, bottomness, and topness are conserved.