Physics Atomic Structure Topic 4 Flashcards
number of protons =
atomic number
number of neutrons equation
mass number - atomic number
Electrons=
protons
the mass and charge of a proton
mass=1
charge=+1
the mass and charge of a neutron
mass=1
charge=0
the mass and charge of an electron
mass= 1/1840
charge=-1
draw the planetary model
Upper number is the
mass number
lower number is the
atomic number
mass number is
mass number is
the mass of protons +nuetrons
Describe radiation in terms of nuclei
Some elements have a naturally unstable nucleus . They become stable again by emitting radiation from their nucleus
How do we measure the amount of radiation emitted from an element ?
- This is called the activity sample , activity is measured in Bequerels (Bq) which are counts per second
Isotopes definition
Atoms of the same element with same number of protons but a different numbers of neutrons
DO NOT INCLUDE ELECTRONS
What charge does the nucleus of an atom have?
positive
Which of the following is not a conclusion from the alpha particle scattering experiment?
the nucleus contained protons and neutrons
Which of the following is never emitted on its own from the nucleus during radioactive decay
proton
Which type of radiation is most penetrating
gamma is a wave and so it is not easily stopped by solid materials.
Which type of radiation is most ionising?
alpha is the largest particle and so it can knock electrons off atoms most easily.
There are 3 types of radiation and symbols
- Alpha α
- Beta β
-Gamma γ
Explain what a alpha particle is :
A helium nuclei, made up of:
- 2 protons - 2 neutrons
It is only the nuclei of a helium atom so there are no electrons
Explain what a beta particle is :
- A neutron changes into a proton and an electron and the electron emitted is quite small and is afast moving or highly energetic electron,
Explain what a gamma particle is :
- It is a wave in the electromagnetic spectrum
- It is a form of light, therefore is not made up of any matter
Charge of alpha particle and mass and penetration power
+2
4 amu
low
Alpha radiation is absorbed by and ionisation power is
high ionising power Thick sheet of paper or card
Charge of beta particle and mass and penetration power
-1
1/2000
medium
Beta radiation is absorbed by and ionisation power is
aluminium meduim
Charge of Gamma particle and mass and penetration power
nuetral
0
high
Gamma radiation is absorbed by and ionisation power is
lead
low
During Alpha Decay the mass number——-
and the atomic number——
decreases by 4
decreases by 2
During Beta Decay the mass number——-
and the atomic number——
stays the same
increases by 1
During Gamma Decay the mass number——-
and the atomic number——
stays the same
stays the same
Ionisation produces :
charged particles
Ionisation is caused by:
- removal of electrons from particles
- gain of electrons by particles
How can you determine whether there is a positive or negative charge caused by ionisation
less electrons- positive charge
more electrons-negative charge
Ionisation is hazardous because:
- It affects the action of molecules eg it can damage DNA and hence affect cell respiration
- It can produce toxins that stop cells working
for example radiation sickness
Precautions of radioactive material
lead lined boxes
tongs/gloves
short time exposed and small amounts
keep distance
not pointing at people
protective clothing
labelled and shielded storage
Irradiation
Is the process by which an object is exposed to radiation
Contamination
radioactive material is deposited on or in a object or a person
In nuclear fission why is the mass of the products before greater than the mass of the products afterwards
because some of the mass has been turned into energy
Control rods what are they made out of and what do they do ?
usually made out of boron they absorb excess neutrons so a chain of reaction does not happen
What would happen without the Control Rods ?
the fission reaction could get out of control and cause a chain reaction
Control rods can be made —— or ———- to ———————– the reaction
higher or lower to control
Describe the chain reaction of nuclear fission
one neutron produces three from fission those three also produces three after that and so on.
After how many reactions do you get a nuclear bomb ?
After 30 reactions you get a nuclear bomb
Nuclear fission summary:
Energy is released in a reactor as a result of a process called nuclear fission . the nucleus of an atom splits into the smaller nuclei. This event can cause other nuclei to split, producing a chain reaction . This energy from each reaction is very small but there are billions of reactions every second . The waste products from these reactions are radioactive which is why nuclear power plants are controversial
Compared to nuclear fission nuclear fusion reactions:
- release even more energy per kg of fuel
- make less radioactive emissions as many of the products are stable (eg He-4)
- use ‘cleaner’ fuel : isotopes of hydrogen , which can be made from water and lithium
Explain nuclear fusion
nuclear fusion occurs when nuclei join (fuse) together
Two small nuclei join to make a single heavier nucleus
The process generates heat energy
Nuclear fusion is the process by which energy is released in stars. Fusion requires extreme high temperatures to overcome electrostatic repulsion
Atoms
Atoms are very small, having a radius of about 1 × 10-10 metres.
The basic structure of an atom
is a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.
The radius of a nucleus is———————–. Most of the mass of an atom
less than 1/10 000 of the radius of an atom
is concentrated in the nucleus.
Explain electron arrangement
The electrons are arranged at different distances from the nucleus (different energy levels). The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level).
Explain electron arrangement
The electrons are arranged at different distances from the nucleus (different energy levels). The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level).
Atoms have no
overall charge
All atoms of a particular element have the same
number of protons..
Before the discovery of the electron atoms were thought to be
atoms were thought to be tiny spheres that could not be divided.
The discovery of the electron led to the
plum pudding model of the atom. The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it
The results from the alpha particle scattering experiment led to the conclusion
that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model.
Niels Bohr adapted the nuclear model by suggesting that
electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr agreed with experimental observations.
The experimental work of James Chadwick
provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.
Activity
is the rate at which a source of unstable nuclei decays.
Count rate is :
the number of decays recorded each second by a detector (eg Geiger-Muller tube).
The emission of the different types of nuclear radiation may cause
a change in the mass and /or the charge of the nucleus.
The emission of a gamma ray does not cause
the mass or the charge of the nucleus to change.
Radioactive decay is
is random.
The half-life of a radioactive isotope is
the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.
Radioactive contamination
Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard
Background radiation is ——— all of the—-. It comes from:
around us time
* natural sources such as rocks and cosmic rays from space
* man-made sources such as the fallout from nuclear weapons testing and nuclear accidents.
The level of background radiation and radiation dose may be affected
by occupation and/or location.
Radiation dose is measured in ————
sieverts (Sv)
1000 millisieverts (mSv) =
1 sievert (Sv)
Nuclear radiations are used in medicine for the:
- exploration of internal organs
- control or destruction of unwanted tissue.
Nuclear fission simplified
is the splitting of a large and unstable nucleus (eg uranium or plutonium).
Spontaneous fission is ——–. Usually, for fission to occur …………………….
rare
the unstable nucleus must first absorb a neutron.
The nucleus undergoing fission splits into
two smaller nuclei, roughly equal in size, and emits two or three neutrons plus gamma rays. Energy is released by the fission reaction.
all of the fission products have
kinetic energy
Nuclear fusion is what simplified
joining of two light nuclei to form a heavier nucleus. In this process some of the mass may be converted into the energy of radiation.
Later experiments
led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles.
gamma rays can travel
tens or hundreds of feet in air
betta rays can travel
up to several yards.
Uses of radioactivity :
put radioactive material (gamma)
into the pipe
if higher reading then there is a leak if no reading then there is a blockage .
- Can use radiation to find leaks and blockages in underground pipes
once figured out where the problem is would have to flush out all the radioactive material
Can also be used for people e.g find out what is wrong with kidneys use a radioactive tracer
radiation in cancer
radiation is al.so used in radiotherapy to treat cancers
cancer cells are more easily damaged by radiation than healthy cells
radiation is fired from many angles to reduce damage to healthy cells
Carbon dating
to find out how old somethingis ( must be made of something that was once living) you use carbon dating
carbon 14
carbon 14 is radioactive when a plant or animal dies it stops absorbing carbon 14 and what it already has starts to decay . Can estimate how old it is by how much carbon is left , You can do this if they knoe the half life
when cant it be used
u cant used carbon dating for anything around 50,000 year old or older so use uranium instead ( not enough carbon 14 left) use uranium for things like dinasour fossils by seeing how much uranium is in the rock around it .
