ATOMIC STRUCTURE Flashcards
describe the basic structure of an atom
nucleus containing protons and neutrons, around which electrons orbit in fixed energy levels
describe the plum pudding model of the atom
sphere of positive charge with negative electrons embedded in it
why do all atoms have no overall charge
equal numbers of positive protons and negative electrons
how small is the nucleus compared to the whole atom
10 000 times smaller
how can an electron move up an energy level
absorb sufficient electromagnetic radiation
what is ionisation
process which adds or removes electrons from an atom
what is formed if an atom loses an electron
positive ion
how does an atom become a negative ion
gains electrons
what is the atomic number of an element
number of protons in one atom of the element
what is the mass number of an element
number of protons and neutrons
which particle do atoms of the same element always have the same number of
protons
what are isotopes
atoms of the same element with the same number of protons but a different number of neutrons
what were the two main conclusions form the alpha particle scattering experiment
- most of the mass of an atom is concentrated in the nucleus
- nucleus is positively charged
what are the three types of nuclear radiation
alpha, beta and gamma
what is gamma radiation
electromagnetic radiation from the nucleus
what type of nuclear radiation is the most ionising
alpha
what is the range in air of alpha, beta and gamma radiation
a few cm, 1m and unlimited
which materials stop alpha, beta and gamma radiaiton
sheet of paper, thin aluminium sheet and thick concrete
which type of nuclear radiation does not cause a change in the structure of the nucleus when it is emitted
gamma
what is radioactive activity
the rate at which a source of unstable nuclei decays
what unit is used to measure the activity of a radioactive source
becquerel
what is count rate
number of decays each second
what is meant by the half life of a radioactive source
time taken for half the unstable nuclei to decay or time taken for the count rate to halve
what is irradiation
exposing an object to nuclear radiation
what is radioactive contamination
unwanted presence of substances containing radioactive atoms on or in other materials
where does background radiation come from
rocks, cosmic rays, nuclear weapons
why are gamma emitting sources used for medical tracers and imaging
pass through the body without causing damage to cells
what is nuclear fusion
when two light nuclei join to make a heavier one
what is nuclear fission
the splitting of a large and unstable nucleus into two smaller nuclei
how does nuclear fission occur
an unstable nucleus absorbs a neutron, it splits into two smaller nuclei, and emits two or three neutrons plus gamma rays
