atomic structure - nuclear chemistry Flashcards
(27 cards)
can nuclei change during reactions?
yes
most reactions leave nuclei unchanged e.g. covalent/ionic bond formation
but some can cause nuclear rearrangements e.g. radioactivity/nuclear fission/fusion
what makes up the nucleus?
protons + neutrons, bound together strongly by nuclear force
what kind of force is nuclear strong force?
it has a short range and drops to 0 just beyond the edge of the nucleus, ~ 2.5fm
at <0.7fm it becomes repulsive between nucleons
proton definition
a subatomic particle with a +ve charge, which provides the attractive electrostatic central force that bind the atomic electrons
atomic number definition
number of protons in a nucleus, this is fixed for an element
these define the entire charge of the nucleus and therefore its chemical identity/the properties of an element
neutrons definition
subatomic particles with a neutral charge - these only affect the mass of the nucleus
isotope definition
variants of an atom/element with the same number of protons but a different number of neutrons - many are often unstable, and rare
what is the role of neutrons in the nucleus?
neutrons reduce electrostatic repulsion within the nucleus
alpha particle definition
a He nucleus , charge +2
beta particle definition
an electron
gamma photon definition
electromagnetic radiation from the nucleus
why do atoms give off radiation?
radiation is given off by radioactive elements as a result of nuclear decay
what are the 3 types of ionising radiation
alpha (most ionising)
beta
gamma (least ionising)
explain the trend in ionising radiation
alpha is the most ionising, as it emits alpha particles which have large mass and large 2+ charge, whereas gamma is the least ionising as it emits gamma photons which have small mass and no charge
half life definition
the rate of radioactive decay
what is alpha decay?
when a He nucleus (alpha particle) is emitted from an atom - this changes the atom into a new element
how does E=mc^2 relate to alpha radiation?
if the decay is an alpha particle, the lost nuclear mass in converted to energy - this relationship is described through this equation
how penetrating is alpha radiation?
not very penetrating, can be stopped by paper as alpha particles are quite large
what is beta decay?
the emission of an electron from a nucleus - this occurs when a neutron is converted into a proton + an electron - this increases atomic no. by 1 changing element, although mass no. stays the same
how penetrating is beta decay?
moderately penetrating, can be stopped by a block of wood or a thin sheet of metal
what is gamma decay?
when nuclei produced by alpha or beta radiation are in meta stable excited states, it can emit a very high frequency gamma photon which will return it to ground state
how penetrating is gamma radiation?
very penetrating, requires a few inches of lead or several feet of concrete to be stopped as gamma photons are so small and so fast
transuranic element definition
elements with proton number > 92 - not naturally occurring, only synthetically made
what makes some elements radioactive?
when plotting neutron number (y) against proton number (x), there is a band of stability - elements which lie below this band of stability are prone to nuclear decay - includes all transuranic elements
