Nuclear Atoms
What did thompson believe the atom was made by?
- A large distribution of positive charge spread over a relatively large area
With Small negatively charged electrons immersed within the positive distribution
Compare Electrical and Gravitational forces
- Both proportional to 1/r²
- Only one kind of mass - so the force is always attractive
- 2 types of charge - therefore electrical charge can be both repulsive and attractive
- Electric force is fundamentally stronger
What is the initial KE of a alpha particles converted to when it gets the closest before being deflected back
EPE (Electrical Potential Energy)
How much EPE does an alpha particle usually have
5MeV (Mega electronvolts)
What range of distance is a strong nuclear force attractive
Between 0.5-3.0fm(FemtoMetres)
What range of distance is a strong nuclear force repulsive
Less than 0.5fm(FemtoMetres)
State 4 feaures of a strong nuclear force
- Acts on all neutrons
- It's a short range force
- It's max attractive value is around 1fm(Typical nuclear separation
- Forces (repulsive and attractive) cancel out (equal zero) after 3fm
Describe Rutherford's experiment
Alpha particles were shot (at a high speed) at a thin gold sheet of foil. Most of them passed through the sheet, showing that the atom is mostly empty space. Some were deflected at small angles showing that the nucleus was +ve charged. A small amount were deflected at large angles showing that the mass of the atom is concentrated at the nucleus.
What did rutherford conclude from his experiment?
The atom has a small dense nucleus which held most of the atoms mass. The atom was also surrounded by orbiting e-'s
Define an Isotope
Atoms with the same number of protons and e-s but a different number of neutrons
What is the approximate radius of a nucleus and how was this found
10^-14, estimated from the distribution of angles in rutherfords experiment
Give the formula for the radius of a nuclei
R = r0(A^1/3)
Name the 4 fundamental forces
- Gravitational
- Electromagnetic
- Weak nuclear
- Strong nuclear
Describe gravitational forces
- Acts on all particles with mass
- Always attractive
- Has an infinite range, however is the weakest force of all fundamental forces
Describe Electromagnetic forces
- Acts on all particles with charge (electrostatic and magnetic)
- Has an infinite range
Describe Weak nuclear forces
- Responsible for beta decay
- Changes quark types over very small distances
Describe Strong Nuclear Forces
- Acts between all nucleons and quarks
- Counteracts the repulsve electrostatic forces between protons in the nucleus
- Attractive at small distances(0.5 - 3fm)
- Repulsive at small distances(<0.5fm)
Give reasons why a nucleus may be unstable
- Has too many neutrons
- Has too many protons
- The nucleon is too heavy
- It has too much energy