What is Thomson’s Plum pudding model?
The atom is a positively charged fluid with symmetrically placed electrons
What is Rutherford’s Model Experiment?
Alpha particles were directed onto gold foil which could allow the particles to penetrate the sheet and be recorded on a screen.
What were the findings of Rutherford’s Experiment?
- most particles passed with little to no deflection
- some were scattered through small but significant angles
- very small # were deflected at very large angles
These findings could not be explained by Thompson’s model.
What was Rutherford’s model?
The atom consists of a small, massive positively charged core (nucleus) surrounded by revolving electrons.
What are the limitations of the Rutherford model?
- cannot explain why electrons didn’t accelerate towards nucleus
- cannot explain why the nucleus didn’t disintergrate
- cannot explain what made up the nucleus to make it positive
What is the Bohr’s Model?
States:
- electrons are restricted to move in certain selected orbits of definite energy levels (in these states electrons do not radiate energy)
- energy is emitted and absorbed by atoms in discrete quanta (energy packets)
- emission of radiation by an electron would be by quantum jumps from one fixed state to another
What are the limitations of Bohr’s model?
- cannot explain the Zeeman effect (the splitting of a spectral line into hyperfine lines when placed in a very strong magnetic field)
- can only be used to describe atoms/ions with 1 electron in the 1st energy level (e.g. Hydrogen)
- cannot explain relative intensity of spectral limes
What are photons?
Discrete units of energy representing the smallest quantity of light at that frequency.
What occurs during alpha decay?
An alpha particle is released and the reactant changes element
Why does alpha decay occur?
If the atom is too big, the atomic number is greater than 83
What occurs during beta - decay?
A neutron turns into a proton, an electron and an antineutrino
What occurs during beta + decay?
A proton turns into a neutron, a positron and a neutrino
What occurs during fission?
A large nucleus splits into two nuclei with smaller mass numbers and usually a neutron is released.
What occurs during fusion?
2 nuclei combine to form a nucleus of a lighter mass number.
What happens in the Frank Hertz Experiment?
- cathode is heated and releases electrons (thermionic emission)
- the electrons are attracted to the mess grid and if they have enough energy they will hit the collecting plate
- when the 1st energy level voltage(e.g. 4.9eV) is applied, the electrons released form the cathode have enough energy to change the energy level of the electrons from the gas
- the energy of the cathode electrons is lowered from these collisions and less of these electrons hit the collecting plate. Therefore the current decreases.
