2b.2 - Electronic structure Flashcards
Describe the experiment that disproved the plum pudding model of the atom
- Fired a beam of alpha particles at thin gold foil
What did they expect from the experiment that disproved the plum pudding model?
Positively charged alpha particles would be slightly deflected by the electrons in the plum pudding model
What actually happened in the Rutherford experiment that disproved the plum pudding model?
Most alpha particles went straight through but the odd one came straight back at them
What is an isotopes?
Atoms with the same number of protons but a different number of neutrons
Why is radioactivity random?
- You can’t say when a nuclei is going to decay
- You can’t make decay happen
What is the three different types of radiation?
Alpha, beta, gamma
What is background radiation?
Radiation that is present at all times, all around us
Where does background radiation come from? (3)
- Unstable isotopes
- Radiation from space
- Radiation due to man made sources
What relative proportion of background radiation is radon gas?
51%
What relative proportion of background radiation is cosmic rays?
10%
What relative proportion of background radiation is rocks and building materials?
14%
What relative proportion of background radiation is from nuclear industry?
1%
What relative proportion of background radiation is medical x-rays?
12%
What relative proportion of background radiation is food?
12%
What is an alpha particle? (2)
- A helium nuclei
- Two protons, two neutrons
How far can alpha particles travel?
They are stopped quickly, even when travelling through air
What are beta particles?
Fast moving electrons
How ionising are beta radiation?
Strongly ionising
How far can beta particles travel?
- Long range in air
- Penetrate moderately into materials
What is gamma radiation?
A very short wavelength of an EM wave
How far can gamma rays travel? (2)
- Penetrate far into materials without being stopped
- pass straight through air
How ionising are gamma rays?
Weakly ionising
What do gamma rays not have?
A mass and a charge
What are the products of alpha decay?
- A helium neucli
- A gamma ray
- The new atom it makes
How do you know what new atom is made in alpha decay?
Take 4 from the mass number and two from the atomic number
What is made as products of beta decay?
- A new atom
- A beta particle
How do you know what new atom is made in beta decay?
Add 1 to the atomic number
Write the nuclear equation for the alpha decay of uranium
238
U
92
- 0
U -> Th. +. He. + Y
- 0
- 0
Write the nuclear equation for the beta decay of Carbon-14
14
C
6
- 0
C ->. N. + e
6 7. -1
- 0
What charge do alpha particles have?
Positive
What charge do beta particles have?
Negative
What are alpha and beta particles deflected by?
Electric and magnetic fields
Why are alpha and beta particles deflected in opposite directions by magnetic or electric fields?
They have opposite charges
Why are alpha particles deflected less even though they have a stronger charge?
They have a much greater mass
Why is gamma radiation not deflected by electric and magnetic fields?
Gamma radiation has no charge
What does radiation dose depend on?
- Type
- Amount
The higher the radiation dose …
…the more at risk you are of developing cancer
What do radiographers do to protect themselves from radiation?
Wear lead aprons and stand behind lead screens
What was the plum pudding model?
- Atoms were spheres of positive charge
- Tiny negative electrons stuck in it like plums in a plum pudding
