atomic structure Flashcards
give an approximation for the radius of an atom
1 x 10^-10 metres
what are the three subatomic constituents of an atom?
-proton
-neutron
-electron
where is the most of the mass of an atom concentrated?
in the nucleus
approximately what proportion of the total radius of an atom is the radius of the nucleus?
1 / 10000
describe the arrangement of protons, neutrons and electrons in an atom
-the protons and neutrons are found in the atom’s nucleus
-the electrons are found in discrete energy levels around the nucleus
what type of charge does the nucleus of an atom have? why?
-positive charge
-nucleus contains protons and neutrons
-protons have positive charge
-neutrons have no charge
give two ways that an atom’s electron arrangement can be changed
-absorbing electromagnetic radiation
-emitting electromagnetic radiation
explain how an atom’s electron arrangement changes when it absorbs EM radiation
-electrons move further away from nucleus
-they move to a higher energy level
explain how an atom’s electron 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?
-number of protons is equal to number of electrons
-protons and electrons have equal and opposite charges so charge cancels
what do all forms of the same element have in common?
same number of protons
what is the name given to the number of protons in an atom?
atomic number
what is an atom’s mass number?
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 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 the 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’s 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 constituents 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?
-a 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
which type of radiation is most ionising?
alpha radiation
which type of radiation is least ionising?
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
-known as peer review
