P6.1 Flashcards
Describe 2 differences between the nuclear model of the atom and the plum pudding model of the atom. [4]
In nuclear model electrons orbit atom.In plum pudding model electrons are scattered throughout atom randomly.
In nuclear model +ve protons located in centre of atom in nucleus.In plum pudding model +ve mass spread out throughout atom.
Why can protons never move out of the nucleus
they are too tightly bound in the nucleus.
What are charged atoms called
Ions
What is an ion
Charges particle =
Different number of electrons
Outside nucleus.
What is an isotope
Isotopes are atoms of the same element containing a different number of neutrons.
What is a radioactive substance
one which contains unstable nuclei that become stable by emitting (nuclear) radiation.
What type of event is a radioactive event
RANDOM EVENT - can’t be predicted / influenced
What is alpha radiation
2 protons + 2 neutrons = helium NUCLEUS
What is beta radiation
A FAST moving electron
What is gamma radiation
High energy EM wave
Properties of alpha radiation
- Stopped by paper/skin
- Heavily ionising
- Slow
Properties of beta radiation
- Stopped by thin aluminium
- Moderately ionising
- Fast
Properties of gamma radiation
- Stopped by thick lead
- Lightly ionising
- Speed of light
Range of an alpha particle in air
A few cm
Range of a beta particle in air
1m in air
Range of a gamma wave in air
Unlimited range
Which types of these radiation are ionising
All 3 forms of nuclear radiation ionise substances/molecules/atoms they pass through.
Ionisation of living cells can damage/kill them.
CLASSIC GRADE 9 EXAM QUESTION“Explain why nuclear radiation is so dangerousto the human body” [4]
Nuclear radiation is highly ionising.
If the ions are created near/in the body, they will react with the cells of the body.
The cells become damaged.
Damaged cells continue to replicate, giving rise to a tumour.
What is ionisation
Ionisation is the process of turning a neutral atom/molecule into an ion
Which type of radiation is most dangerous outside of the body
Gamma = most dangerous because can penetrate the skin
Which type of radiation is least dangerous outside of the body
α = alpha = least dangerous because it can’t penetrate skin
Which type of radiation is most dangerous inside the body
α = most dangerous because it is heavily ionising
Which type of radiation is least dangerous inside the body
Gamma = least dangerous ∵ can penetrate the body and leave it
Relationship between penetrating power and ionisation potential
As penetrating power increases, the ability to create ions, ionisation potential decreases.
Which type of radiation has the highest ionisation potential
Alpha
Which type of radiation has the lowest ionisation potential
Gamma
Which type of radiation has the highest penetrating power
Gamma
Which type of radiation has the lowest penetrating power
Alpha
Charge of an alpha particle
+2
Charge of a beta particle
-1
Charge of a gamma wave
0
How to separate a beam containing all three of these types of radiation
What is background radiation
Nuclear radiation that is around us from our environment or space
Example of background radiation
Hospitals
NOT PHONES!!
- Place the radioactive source in front of the Geiger counter with nothing in-between and record the activity.(activity is defined as the number of emissions of ∝, β and/or γ per second)
- Place a piece of paper in-between counter and source.If activity falls, your source is emitting ∝.
- Place a thin metal foil in-between counter and source.If activity falls, your source is emitting β.
(be careful here… γ passes through everything)If after placing the thin metal foil in-between counter and source and there is still activity being recorded, your source is emitting γ.
Are neutrons, more or less ionising then alpha particles
- As neutrons have a zero charge, they cannot exert a force of repulsion or attraction upon other particles.
- Neutrons are also smaller than alpha particles.(so they more easily “pass by” other particles)
- This makes neutrons less ionising than alpha particles.(it also makes them more penetrating as a result)
Nuclear equations = alpha decay
The number of protons and neutrons changes.
nucleus loses 2 protons and 2 neutrons]
Nuclear equations = beta decay
The number of protons changes.[neutron to proton]
neutron number decreases by 1
proton number increases by 1
as a neutron turns into a proton and an electron
(only electron ejected from nucleus at a high speed)
What is Neutron decay
Some nuclei have too many neutrons
.[nucleus emits neutron]
Does alpha decay change the mass number or proton number
BOTH
the mass number decreases by 4
the atomic number decreases by 2
the nuclear charge decreases by 2
Does beta change the mass number or proton number
Proton number
the mass number stays the same
the atomic number increases by 1
the nuclear charge increases by 1
Define half life
The time taken for half the unstable nuclei in a radioactive substance to decay.
Define activity
The number of nuclei that decay every second.
How can you measure activity of a radioactive substance
Geiger counter
A sample of radioactive isotope contains 32 million atoms of the isotope. How many atoms of the isotope are present after;
One half life?
5 half lives?
Where is the lowest energy level found in an atom
The lowest energy level is closet to the nucleus.
How can Electrons in low energy levels move up to a higher energy
By gaining energy by absorbing EM radiation
What is the term used to describe when an electron gains energy and moves up to the next energy level
electrons are EXCITED to higher energy levels.
How does exciting electrons work
1, A single photon is absorbed entirely by a single electron.
- The energy of the photon is directly proportional to the frequency of the EM radiation.
- If the energy of the photon exactly matches the difference in energy between two levels, the electron will excite to a higher energy level.
What MUST be the same if an electron can move up to the next energy level
the energy of the photon must EXACTLY match the difference in energy between two levels
Why do electrons de-excite
Only a certain number of electrons are allowed to exist at any given energy level.
Thus, electrons that have excited to higher energy levels, will de-excite and return to their original energy level.
What happens when electrons de-excite
they emit energy as photons again.
How do electrons de-excite - 4 things to say
ONE - An excited electron will de-excite andreturn to its original energy level.
TWO - The electron will de-excite in steps.
THREE - Each time it de-excites, it emits energy in the form of a photon of a given frequency.
FOUR - The emitted photons are of lower energy (and lower frequency) than the original photon that was
absorbed and caused excitation.
Describe the difference between an excited atom and an ionised atom
In an excited atom, orbital electrons are in a higher energy state/level.
In an ionised atom, orbital electrons have left the orbitals/energy levels of the atom.
Suggest and explain why hydrogen cannot emit x-ray photons
The energy of emitted photons is equivalent to theenergy difference between energy levels in an atom.
Hydrogen energy levels must not have a difference large enough to give rise to high energy X-ray photons.
NEED TO KNOW THIS - explain why some atoms can absorb ultraviolet radiation but emit visible light ( and so can glow in the dark )
Some atoms absorb UV radiation, as there exists an energy difference between their energy levels, that exactly matches the energy of the UV photons.
After absorbing a UV photon, an orbital electron will excite to a higher energy level.
The excited electron will then de-excite to its original energy level, in steps, emitting photons of energy equivalent to the energy difference between levels.
The energy difference between the levels matches the energy of visible light photons. + emits that
