Download 14-2 Notes Atomic number

14-2 Notes
Atomic number-number of protons in the nucleus of
an atom
Uranium is heaviest naturally occurring element=92
protons
Isotopes-atoms of the same element that have
different numbers of neutrons
Mass of the protons and neutrons make up the
nuclear mass of the atom
Carbon-12, Carbon-13, Carbon-14
If proton # = neutron # then it is a stable atom
Mass number = proton # + neutron #
Strong nuclear force--holds protons together in the
nucleus
Atomic nuclei are stable when proton number is = to
neutron number
(esp. true in larger nuclei—Pu, U)
When the nucleus releases particles to become more
stable, energy is given off. This is called radioactive
decay. (release of particles and energy)
Transmutation--changing of one atom into another
because of release of protons
Alpha particle—2 protons and 2 neutrons
Americium-241 releases energy and particles called
nuclear radiation (in smoke detectors- when
electricity is disrupted the alarm sounds)
A neutron can become unstable and turn into a proton
and electron--beta decay
H-3 (isotopes) goes through beta decay and 1 neutron
turns into a proton, and electron. This causes it to be
an isotope of He.
Radioactive decay is random.
Half-life—amount of time it takes for half of the
nucleus of an atom to decay
Carbon-14 has a half-life of 5730 yrs. Starting with
100 g of carbon-14, how much would be left after
17,190 yrs?
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Radioactive decay of unstable atoms is unaffected by
weather, pressure, magnetic or electrical fields, or
chemical reactions
C-14 (carbon-14) is used to determine the age of once
living things (half life =5730 yrs)
U-238 (uranium-238) is used in determining the age
of rocks (half life=4.5 billion years)
Nuclear waste is buried in Carlsbad, NM. 655 m
underground
Alpha and beta particles are smashed into other
elements that can absorb them and form new
elements
Tracer elements are used to diagnose disease and
study environmental conditions
These isotopes have very short half-lives so
organisms are not subjected to much radiation.
I-131 is used to diagnose thyroid problems
Radon-222 has a half-life of 3.8 days. Starting with
50 g of radon-222, how much would be left after 19
days?