Radioactivity Flashcards
What is the approximate radius of an atom?
around 1×10-10 metres.
What is an atom?
atom
The smallest part of an element that can exist.
What defines an element?
The number of protons
What is the mass number?
The number of protons and neutrons found in the nucleus of an atom.
What is the atomic number?
The number of protons in the nucleus of an atom. Also called the proton number.
What can mass number also be called?
The nucleon number
What can the atomic number also be called?
The proton number
What happens when an atom becomes ionised?
number of electrons will change
What is an ion?
An ion is an atom that has lost or gained one or more electrons.
What did the Ancient Greek philosopher Demokritos think that matter was?
thought that matter was made up of millions of tiny, uncuttable pieces of that same matter
Where does the word atom come from?
Comes from the word atomos which means uncuttabls
Who discovered the electron?
J J Thomson
What year did J J Thomson discover the electron?
In 1897
What did J J Thomson propose about the atom?
proposed that the atom looked like a
plum pudding
What is the plum pudding model?
The scientific idea that an atom is a sphere of positive charge, with negatively charged electrons in it.
What was the evidence available to Thomson at the time he discovered the plum pudding model?
1.solids cannot be squashed, therefore the atoms which make them up must be solid throughout
2.rubbing two solids together often results in static charge so there must be electrons on the outsides of atoms which can be transferred as atoms collide
Who did an experiment to test the plum pudding model?What year was the experiment carried out?
In 1905, Ernest Rutherford with his 2 students Hans Geiger and Ernest Marsden
How did Rutherford test the plum pudding model?
They directed a beam of alpha particles at a very thin gold leaf suspended in a vacuum
What are alpha particles a form of?
Nuclear radiation with a large positive charge
Why was the vacuum important when testing the Plum pudding model?
any deflection of the alpha particles would only be because of collisions with the gold foil and not due to deflections off anything else.
What did they expect the alpha particle to do when testing the Plum Pudding model?
It was thought that the alpha particles could pass straight through the thin foil, or possibly puncture it
What did they actually find when then tested the Plum pudding model?
1.most of the alpha particles did pass straight through the foil
2.a small number of alpha particles were deflected by large angles (> 40°) as they passed through the foil
3.a very small number of alpha particles came straight back off the foil
The fact that most alpha particles went straight through the foil is evidence for? (PP model)
the atom being mostly empty space
What does A small number of alpha particles being deflected at large angles suggest? (PP model)
there is a concentration of positive charge in the atom. Like charges repel, so the positive alpha particles were being repelled by positive charges.
What does The very small number of alpha particles coming straight back suggest? (PP model)
the positive charge and mass are concentrated in a tiny volume in the atom (the
nucleus
).
What does the positive charge and mass are concentrated in a tiny volume mean?
the chance of being on that exact collision course was very small, and so the ’target‘ being aimed at had to be equally tiny.
What had Rutherford discovered about the atom?
the nuclear atom, a small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom.
Who made the discovery of the make-up of the nucleus?
It came much later, and was not made by Rutherford
What size was the nucleus Calculated to be after Rutherfords experiment?
about 1/10,000th the size of the atom.
How can an atoms nucleus only be stable?
if it has a certain number of
neutrons
for the number of
protons
it has
How stable are elements with fewer protons?
the ones near the top of the
periodic table
, are stable if they have the same number of neutrons and protons,
What happens to the stability of the Nucleus as the number of protons increase?
More neutrons are needed to keep the nucleus stable
What happens to nuclei with too many or too little Neutrons
unstable and will
decay
, in a random process, emitting
radiation
.
What is radiation?
Energy carried by particles from a radioactive substance, or spreading out from a source.
What is radioactive decay?
The process in which unstable atomic nuclei break apart or change, releasing radiation as they do so.
An unstable
nucleus
can decay by emitting what?
1.an alpha particle
2.a ß- (beta minus) particle
3.a ß+ (positron)
4. a gamma ray
or in some cases a single
neutron
.
If the nucleus is unstably large what will it emit?
an alpha particle.
What is an alpha particle?
a ‘package’ of two protons and two neutrons
What nucleus does an alpha particle contain?
An alpha particle is also a helium-4 nucleus
so it is written as 4
2He. It is also sometimes written as 4
2α.
What does alpha decay do to the mass and atomic number?
It causes the mass number
of the nucleus to decrease by four
and the atomic number
of the nucleus to decrease by two.
What happens if the nucleus has too many neutrons?
neutron will turn into a beta minus (β-) particle-known as beta radiation
What is a beta minus (β-) particle?
neutron will turn into a proton and emit a fast-moving
electron
.
What is the relative mass and mass number of a beta particle?
0 for both
What is a beta particle a electron,neutron or proton?
An electron so written as 0
-1e. However, sometimes it is also written as 0
-1β.
Where has the beta particle come from in the atom?
The beta particle is an electron but it has come from the nucleus, not the outside of the atom.
What can neutrons be split into?
neutrons can split into a positive proton (same mass but positive charge) and an electron (which has a negative charge to balance the positive charge)
What happens to the neutron once it has been split?
It is then ejected at high speed and carries away a lot of energy.
What does beta decay do to the atomic and mass numbers?
Beta decay causes the atomic number of the nucleus to increase by one and the mass number remains the same.
What will happen if a nucleus has too few neurons?
A proton will tern into a beta plus (β+) particle
What is a beta plus (β+) particle?
proton will turn into a neutron and emit a fast-moving positron- this is called positron emission
