Physics (P4) Flashcards
What is an atom?
The smallest piece of an element that still has the properties of that element
A building block of matter
What is the size of the average atom?
1 × 10-10 or 0.1nm
What is a sub-atomic particle?
A particle that makes up the atom:
Protons
Neutrons
Electrons
What is the atomic nucleus?
The central part of the atom
What is the mass and charge of a proton?
Mass= 1
Charge= +1
What is the mass and charge of a neutron?
Mass= 1
Charge= 0
What is the mass and charge of an electron?
Mass= 0
Charge= -1
What is the overall charge of an atom?
Neutral
What is the charge of the nucleus?
Positive
What does the mass number tell you?
Total number of protons and neutrons
What does the atomic number tell you?
Number of protons
Which sub-atomic particles are in the nucleus?
Protons and Neutrons
Which sub-atomic particles orbit the nucleus?
Electrons
Which sub-atomic particle defines which element the atom is?
Protons
e.g if it has 2 protons it must be a helium atom
Explain why atoms are overall neutral?
Protons are positive
Electrons are negative
Atoms have the same number of protons and electrons so they cancel each other out
What is an isotope?
Atoms of the same element with a different number of neutrons
What is an ion?
An atom that is charged because it has lost or gained eletrons
What are the number of protons, neutrons and electrons in
19
F
9
Protons=9
Neutrons=10
Electroms=9
What was the ‘‘Plum pudding’’ model of the atom?
Negative charges spaced in a positive dough
Who discovered the ‘‘Plum pudding’’ model?
J.J Thompson
Describe the ‘‘Plum pudding’’ model?
The atom is a ball/sphere of positive charge with negative electrons embedded in it.
What is the ‘‘Nuclear’’ model of the atom?
Positive central nucleus surrounded by negative electrons
Most of the atom is empty space
Who discovered the ‘‘Nuclear’’ model?
Rutherford
Give 3 characteristics of the ‘‘Plum pudding’’ model
-Mass is evenly distributed
-Negative electrons are distributed throughout the atom
-The to is mostly a positively charged ‘‘dough’’
Give 3 characteristics of the ‘‘Nuclear model’’
-Mass in concentrated at the centre
-Electrons orbit the nucleus at a distance
-The atom is mostly empty space
Describe Rutherford’s Nuclear model
Electrons orbit around the nucleus at a specific distance
Describe the Gold foil experiment by Rutherford,
· Alpha particles directed towards a piece of gold foil.
· Most particles pass straight through foil
· Some is deflected through small angles
· Very small number of alpha particles are deflected back at the alpha source
State 3 conclusions from the gold foil / alpha scattering experiment
1) mass of an atom is concentrated in a nucleus in the centre
2) nucleus is positive
3) Atom is mostly empty space
What did Neil Bohr discover?
Electrons orbit the nucleus in shells (at specific distances from the nucleus)
When is energy level high?
When the electron is further away from the nucleus
What happens if electrons are given energy?
They can move up energy levels
What needs to be absorbed for an electron to move to a higher energy level?
Photon
Electromagnetic wave
What happens in the ground state?
Electron is closest to the nucleus and has the lowest energy
What happens in the absorption state?
Electron absorbs energy from EM wave of photon
What happens in the excitation state/
Electron goes up an energy level
What is de-excitation?
Electron have too much energy and emits energy to go down to a lower energy level
What is ionistaion?
Removal of electrons from atoms leaving them with an overall charge
What change causes an atom to emit light?
De-excitation
What makes an atom radioactive?
Has an unstable nucleus and therfore releases energy in the form of particles or EM waves
How can an unstable nuclei become stable?
It can decay by giving out certain types of radiation
What is radioactive activity?
The number of particles emitted per second
What is count rate?
The measure number of particles detected per second
What is the unit for radioactive activity?
Becquerels
What type of process is radioactive decay?
Random process
What is the equipment for measuring radiation?
Geiger-Muller tube or Geiger counter
Name the 3 types of nuclear radiation
Alpha
Beta
Gamma
Describe the structure of an alpha particle
2 neutrons & 2 protons (helium nucleus)
What is a beta particle?
A high energy electron
What is a gamma ray?
A high energy electromagnetic wave from the nucleus
What is the mass and charge of an alpha particle?
Mass= 4
Charge= +2
What is the mass and charge of beta?
Mass= 0
Charge= -1
What is the mass and charge of gamma?
Gamma doesn’t have a mass or charge
How does beta decay occur?
A neutron from the nucleus decays to make a proton and an electron. The electron exits the as a beta particle and the proton stays in the nucleus
How is the nuclear equation written?
Unstable → stable + radiation
nucleus nucleus
How far can alpha travel?
Only travels a few cm though air
How far can beta travel?
Up to 1m
How far can Gamma travel?
Many kilometres
Which radiation is mostly penetrating?
Gamma
Which radiation is the least penetrating?
Alpha
Describe the ionising power of Alpha, Beta and Gamma
Alpha – strongly ionising
Beta – weakly ionising
Gamma – very weakly ionising
Which material can stop Alpha?
Paper
Which material can stop Beta?
Aluminium
Which material can stop Gamma?
Thick lead
Define ‘Half-life’ ?
The time taken for half of the radioactive nuclei to decay
If there are 1000 nuclei in a radioactive sample, how many should be left after 2 half-lives?
1000 → 500 → 250
After one half-life which things will halve?
Number of unstable nuclei
Mass of radioactive isotope
Activity
Count rate
What is Irradiation?
When an object is exposed to radiation (The object is now radioactive)
What is Contamination?
When radioactive material gets onto or in an object (The object is now radioactive)
What is direct radiation damage caused by?
Mostly caused by alpha and beta by hitting the skin and transferring energy
What is indirect radiation damage caused by?
Mostly caused by gamma by ionising atoms in cells
Define ‘background radiation’
Radiation around us all the time.
State 4 natural sources of background radiation
Radon Gas
Rocks
Soil
cosmic rays
Where does most background radiation come from?
Radon gas
What is radon gas?
Radioactive gas produced by rocks that have small amounts of uranium
State 3 man made sources of background radiation
· Fallout from nuclear weapons
testing
· Nuclear accidents
· Nuclear Power stations
State 2 medical uses of radiation
Radioactive traces
Radiotherpy
State the risk of using radiation
Tissue damage
Would a long or short half-life radioactive material be more dangerous in the long term?
Long half-life material.
What kind of radiation is used to look at internal organs?
Beta
What is radioactive traces used for?
Diagnosis
Which nuclear radiation is used for radioactive traces?
Beta and Gamma
What kind of radiation is used to look at internal organs?
External
