atomic structure Flashcards
give an approximation for radius of an atom
1x10(-10) metres
what are the three subatomic constituents of an atom
- neutron
- electron
- proton
where is the most of the mass of an atom concentrated?
in the nucleus
approx what proportion of total radius of an atom is the radius of the nucleus
1/10,000
describe the arrangement of protons, neutrons and electrons in an atom?
- the protons and neutrons are found in the atoms nucleus
- the electrons are found in discrete energy levels around the nucleus
what type of charge does the nucleus of an atom have
- positive charge
- the nucleus contains protons and neutrons
- protons have a positive charge
- neutrons have no charge
give two ways that an atoms electron arrangement can be changed?
- absorbing electromagnetic radiation
- emitting electromagnetic radiation
explain how an atoms electrons arrangement changes when it absorbs EM radiation
electrons move further away frim the nucleus
the move to a higher energy level
explain how an electrons arrangement changes when it emits EM radiation
electrons move closer to the nucleus
they move to a lower energy level
how does the ratio of electrons to protons in an atom result in the atom having no overall charge
the number of protons is equal to the number of electrons
protons and electrons have equal and opposites charges, so the charge cancels
what do all forms of the same element have in common
they all have the same number of protons
what is the name given to the number of protons in atom
atomic number
what is an atoms mass number
the total number of protons and neutrons in the atom
what is an isotope of an atom
an atom of an element that has a different number of neutrons, but the same number of protons
how do atoms turn into positive ions
they lose one or more of their outer electrons
electrons are negatively charged, so the resultant charge of the atom is positive
what may lead to a scientific model being changed or replaced?
the discovery of the new experimental evidence which doesn’t agree with the existing theory
how did the plum-pudding model describe the atom
a ball of positive charge, with negatively charged electrons distributed evenly throughout it
prior to discovery of the electron what was believed about the atom?
the atom was believed to be indivisible
which experiment led to the plum-pudding model being discarded?
rutherford’s alpha-scattering experiment
what is the name given to the currently accepted model of the atom?
the Bohr nuclear model
state the conclusions of the alpha-scattering experiment
- most of the mass of the atom is concentrated at the centre in the nucleus
- the nucleus is positively charged
what reinforces a scientific theory?
when experimental results agree with the hypothesised theoretical calculations and theories.
what did James Chadwick experiments on the atom prove?
the existence of neutrons
why do unstable nuclei give out radiation?
- unstable nuclei undergo decay to become more stable
- as they release radiation their stability increases
what is the name of the process in which an unstable nucleus gives out radiation to become more stable?
radioactive decay
define the activity of an unstable nucleus
activity is the rate of decay of a source of unstable nuclei
what is the unit of radioactive activity?
becquerel (Bq)
what is count rate?
the number of radioactive decays per second for a radioactive source.
give an example of a detector that may be used to measure count-rate?
geiger-muller tube
state four types of nuclear radiation?
- alpha particles
- beta particles
- gamma rays
- neutrons
what are the four components of an alpha particle?
- two protons and two neutrons
- it is the same as a helium nucleus
what is the range of an alpha particle through air?
a few centimetres (normally in the range of 2-10cm)
what will stop beta radiation from passing through a point
- thin sheet of aluminium
- several metres of air
what will stop gamma radiation from passing through a point
- several centimetres of lead
- a few metres of concrete
what type of radiation is the most ionising?
alpha radiation
least ionising type of radiation
gamma radiation
state any changes to mass or charge that occur due to the emission of a gamma ray
both mass and charge remain unchanged
describe the nature of radioactive decay
- random
- which nuclei decays and when is determined only by chance
- it is impossible to predict which nuclei will decay and when
define the half-life of a radioactive isotope
- the time it takes for the number of unstable nuclei in a substance to halve
- the time it takes for the count rate from a sample to fall to half its initial level
what is radioactive contamination?
the presence of unwanted radioactive nuclei on other materials
what is irradiation?
- the process of exposing a material to nuclear radiation
- the material does not become radioactive
why is It important for the results of studies on the effects of radiation to be published and shared with other scientists?
- to allow the findings to be independently checked
- this is known as peer review
give 4 sources of background radiation?
- rocks
- cosmic rays from space
- nuclear weapon testing
- nuclear accidents
how should background radiation be dealt with in calculations?
the background count should be subtracted from any readings before half-life calculations were attempted.
what is the unit used to measure radiation dosage?
sieverts (Sv)
how many millisieverts equal 1 sievert?
1000 millisieverts = 1 sievert
why might the radiation dosage that different people experiment differ?
- some occupations involve working with radiation
- background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing
what factors determines how dangerous a particular radioactive isotope is?
the half-life of the isotope
why are isotopes with long half-lives particularly harmful?
- they remain radioactive for much longer periods of time
- they must be stored in specific ways to avoid humans and the environmental from being exposed to radiation for too long.
state two uses of nuclear radiation in the field of medicine?
- examining of internal organs
- controlling and destroying unwanted tissue
how is radiation used in sterilisation?
gamma emitters are used to kill bacteria/parasites on equipment
explain the process of radiotherapy
- gamma emitters direct gamma rays at the cancerous cells
- the cancerous cells absorb the radiation and are killed
how are medical tracers chosen
they should have a short half-life and decay into a stable isotope which can be excreted
they should only release gamma radiation since it is weakly ionising and can be easily pass through tissue without damaging.
what is nuclear fission
the spitting of a large, unstable nuclei to form smaller more stable nuclei (the emission of spare neutrons)
give an example of a fissionable isotope?
uranium -235
what usually needs to happen to include fission
- the unstable nuclei must absorb a neutron
- spontaneous fission (where no neutron absorption occurs) is rare
what is emitted in a fission reaction, besides two smaller nuclei
- two or three neutrons
- gamma rays
- energy
what form of energy do all fission products have?
kinetic energy
what takes place during a chain reaction in a nuclear reactor?
- an unstable nucleus absorbs a neutron
- the nucleus undergoes fission and releases 2 or 3 further neutrons
- these induce more fission, which results in a chain reaction
what is the consequences of an uncontrolled chain reaction?
the rate of fission events become to high and result in the production of too much energy
this can lead to a nuclear explosion
what are the three main components of the core of a nuclear reactor?
- fuel rods
- control rods
- moderator
what is the role of the moderator in a nuclear reactor?
to slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission.
how is the chain reactor in a fission reactor kept under control?
control rods are positioned between fuel rods
the rate of fission is controlled by moving these rods up and down
the lower the rods are inserted, the slower the rate of fission
what term is used to describe nuclei in which fission can be induced through the absorption of neutrons
fissile nuclei
what is nuclear fusion?
the joining of two light nuclei to produce a heavier nuclei and release energy
name two isotopes of hydrogen which are commonly used in nuclear fusion
deuterium and tritium
which releases more energy:
nuclear fission or nuclear fusion?
nuclear fusion
explain the difficulty of generating energy through nuclear fusion?
fusion requires very high temperatures which in itself requires large quantities of energy and also requires casting which can withstand said high temperatures
explain why nuclear fusion is currently not a viable way to produce energy on earth
with current equipment and techniques the energy required is greater than the energy produced, resulting in overall energy loss
