P4 : atomic structure
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give an approximation for the radius of an atom
1 x 10^-10
what are the 3 subatomic constituents of an atom
• proton • neutron • electron
where is 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
1/10,000
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 -the nucleus contains protons and neutrons -protons have a 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 changed when it absorbs EM radiation
-electrons more further away from the 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
-the number of protons is equal to the 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
they all have the 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
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 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 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