Atomic structure Flashcards
what model is used to describe the atom in radiography
the Bohr (planetary) model
what is shown in this model:
electrons (-ve_ orbit the nucleus (+ve) at discrete energy levels often called shells
inside the nucleus there are
protons (+ve charge) and neutrons (zero electric charge)
therefore the overall charge of the nucleus is
positive
electrons have a…
negative charge
electron shells are often referred to as
k, l, m, n
depending on their distance (energy level) from the nucleus
what is meant by the term ‘principal quantum number’ or ‘n’
their electron shell
e.g. K is 1, L is 2, M is 3 etc
an electron shell cannot contain
more than 2n^2 electrons (where n is the principal quantum number)
the outer shell cannot contain more than
8 electrons
describe the symbol, location, mass and electric charge of: a proton
symbol= p
location=nucleus
mass=1.00
electric charge=+1
describe the symbol, location, mass and electric charge of: neutron
symbol=n
location=nucleus
mass=1.00
electric charge=0
describe the symbol, location, mass and electric charge of: an electron
symbol=e
location=orbiting the nucleus
mass= 1/1840
electric charge=-1
what is the atomic number and where would you find it in relation to the element’s symbol
the number of protons in the nucleus
found below the element’s symbol
what is the atomic mass number and where you find it in relation to the element’s symbol
total number of protons and neutrons in the nucleus
found above the element’s symbol
what are isotopes
varieties of an element (also have the same atomic number) which have a different number of neutrons in their nucleus (and hence have a different mass number) Their physical and chemical properties may be different.
what are radioisotopes
isotopes that have an unstable nuclei
what the electron binding energy
amount of energy which must be absorbed by the electron to completely remove it from the atom.
It differs from shell to shell and element to element
How does electron binding energy change as you go from the inner shell to the outer most shell
electrons in the inner shell have a higher electron binding energy than those in the outer shells, because they are closer to the positive charge of the protons in the nucleus and are more strongly attracted to it
what is the unit for electron binding energies
kiloelectronvolts (keV)
what happens during ionisation
when an electron in a shell has absorbed sufficient energy to overcome its binding energy, e.g. by irradiating it with x-rays, then the electron can escape from the atom, leaving behind a charge imbalance and a vacancy in its shell.
before ionisation the atom is electrically neutral, afterwards…
the atom is positively charged an is referred to as a positive ion. there is now a ‘vacancy’ in one of its shells
after ionisation, an electron moves in from the next shell to fill the vacancy, what does it emit?
a photon of electromagnetic radiation (emr), whose energy is equal to the difference in binding energies of the shells involved
what is excitation
when an electron absorbs an amount of energy that is less than its binding energy. it is unable to be ejected from the atom, but can only be raised to a higher energy level, this is called excitation.
what happens to atoms in an excited state
they are unstable and quickly return to the lower energy state with th emission of excess energy in the form of a photon of electromagnetic radiation, of energy equal to the difference in binding energy of the 2 shells involved in the transition
what is the nuclear binding energy
the energy expended in keeping the nucleus together
when is a nucleus said to be stable
when the binding energy is sufficient to keep the nucleus together
what influences nuclear stability
the relative number of protons and neutrons
nuclides with a large number of neutrons tend to be
unstable
what happens when the nucleus becomes unstable
this is the basis of the phenomenon of radioactivity
what is radioactivity
the emission of excess energy from the nucleus of an atom as it attempts to adopt a more stable state
