Section 4 - Radioactivity Flashcards
What did JJ Thomson find in 1897?
What model did he suggest? What did it look like?
Jj Thomson discovered that electrons could be removed from atoms.
Suggested the plum pudding model, the atoms were like spheres of positive charge with tiny negative electrons stuck in them like in a fruit plum pudding
What did Rutherford do?
What did Rutherford expect?
Rutherford tried firing a Beam of alpha particles at thin gold foil. They expected particles to pass straight through the gold sheet or be slightly deflected..
What actually happened in Rutherfords alpha particle experiment ?
Most of the particles went straight through some were deflected more than expected, very few were deflected back the way they had come , something the plum pudding model couldn’t explain
What 3 things did Rutherford realise as a result of his experiment?
1)Rutherford realised that this meant most of the mass in the atom was concentrated at the centre in a nucleus.
2) most of the atom is empty space
3)the nucleus must have a positive charge since the positive alpha particles were repelled
How did Niels Bohr tweak Rutherfords findings?
Niels Bohr proposed that the electrons were in fixed orbits at set distances from the nucleus. These orbits were callled energy levels
Relative mass of a proton
Charge of a proton
Relative Mass of proton=1
Relative charge of a proton = +1
Relative mass of a neutron
Relative charge of a neutron
Relative mass of a neutron =1
Relative charge of a neutron =0
Relative mass of an electron
Relative charge of an electron
Relative mass of electron = 0.0005
Relative charge of electron =-1
What’s the structure of an atom?
Protons and neutrons in the nucleus
Negative Electrons on fixed shells orbiting the nucleus
Why is an atom neutral ?
Number of protons = the number of electrons
What’s it called if an atom looses an electron?
Positive ion
What’s it callled if an atom gains an electron?
It’s called a negative ion if an atom gains an electron
What can atoms join together to form?
Molecules
What can happen to an electron if it absorbs too much electromagnetic radiation and is “excited”
What happens when the electron falls back to its original energy level?
If an electron is “excited” it will move up a shell.
When an electron falls back to its original energy level, it emits the same amount of energy it absorbed, this can often be seen as visible light .
What happens if an atom looses an electron?
An atom is ionised if it looses an electron.
The atom is now a positive ion because there are more protons than electrons.
What do atoms of the same element have ?
Atoms of the same element all have the same number of protons
What is the number of protons in an atom called?
Atomic number or proton number
What is the mass number of an atom?
Number of protons + neutrons
What are isotopes?
Isotopes are different forms of the same element.
They have the same number of protons but a different Number of neutrons (mass number)
What is radioactive decay?
Unstable isotopes decay into other elements and give oht radiation as they try to become stable.
What are the types of ionising radiation radioactive substances release ?
Alpha
Beta
Gamma
Also neutrons
What are alpha particles.
How well do they penetrate material, how far can they travel
How ionising are they?
-An alpha particle is 2 neutrons and 2 protons. It’s shown as 4/2
-They are not very penetrating and are stopped quickly. They can only travel a few cm in the air
-because of their size they are strongly ionising
What’s a beta- (B-)particle ?
Range and how penetrating is it
How ionising is it
A beta minus particle is a fast moving electron released by the nucleus because a neutron has been changed to a proton . No mass, charge of -1.
It’s 0/-1
Moderately ionising
Range of a few metres absorbed by a sheet of aluminium
What is a beta + particle ?
How ionising is it and what is its range ?
-A beta + particle is a fast moving positron. The positron is the antiparticle of the electron . This means it has the same mass as the electron but a positive 1 charge. 0/1
-smaller range
-moderately ionising