Chapter 33: Radioactivity

1

• Chapter 33 Radioactivity
• Atomic Structure pg. 637-8 fig. 33.5 33.7 33.8
  
• The atomic nucleus composed of _____________ and
  __________
• Protons (__ charge) neutrons (___ charge).
• Nucleons (p and nos) nearly _______ times more
  massive than electrons.
• In a neutrally charged atom there is an
  __________ number of protons and electrons (the
  magnitude of the charge of electrons and protons
  is the same but opposite in __________).
• Positively charged protons hold negatively
  charged electrons in their ___________.
• When an atom gains or loses electrons it becomes
  an ________ (if more p than e- it is a
• ___ charged cation, if more e- than p than a
  ___ charged anion).
• Chemical properties of an element determined by
  the numbers of __________.
• (_________number-identifies the element).
  
• Numbers of nos has no effect on the electron
  orbits (wont effect the chemistry of the
  element).
• no act as a ___________ to hold the nucleus
  together (adds to the nuclear _________
  force/force holding nuclear particles together)
  to overcome repulsive forces of ps for each
  other.
• The greater the number of ps in a nucleus, the
  greater the number of nos required to hold the
  nucleus together (for light elements there can be
  nearly _________ numbers of nos and ps / very
  heavy elements there are many _________ nos than
  ps).
• Unpaired no decays into a p and an e- (an e- is
  a ____ particle).
• For a nuclear reaction, mass of products is
  ______ than mass of reactants. Mass converted
  to energy (E mc2).
• All elements above the atomic of _____ are
  radioactive (too many nos required to hold the
  nucleus together, unpaired nos decay).

neutrons protons
no
2000
equal
sign
orbits
ion

-
protons
atomic
strong
cement
equal
more
ß
less
83
2

• 3 distinct modes of decay pg. 635-6 fig. 33.3
  33.4
• Alpha ( a ) decay-a ________ nucleus (42 He2).
• Beta ( ß ) decay- an ______________ (0-1e) .
• Gamma ( ? ) highest _________ (shortest ?) EM
  radiation.
• Alpha least penetrating Gamma most penetrating.
• Radioactive Isotopes pg. 638
• Elemental isotopes have _________ numbers of
  ps but different numbers of _________
• (isotopes of same element have different mass
  numbers).
• Symbols of elements are written as follows mass
  atomic Element for example 146C
• Atomic mass a _____________ average of all the
  isotopes of an element
• Isotopes will vary in their degree of
  __________________.
• Half-Life pg. 641-2 fig. 33.9
• Radioactive elements decay at different
  _________.
• Half-life ________ required for ½ of a substance
  to decay.
• Example If you have 40 g of sample and the
  half-life is 2 years, how much of the 40 g will
  remain after 2 years? ____ g after 6 years?
  ____ g
• Transmutation of Elements pg. 645-6 fig. 33.4
• Transmutation New nucleus formed from a
  nuclear change.
• Transmutations represented by chemical equations
  (the sum of the mass and atomic s of reactants
  is _________ to products)

helium
electron
energy
equal
neutrons
weighted
radioactivity
rates
time
20
5
equal
3

• Nucleus composed of p and no
• Nucleon (p or n0 nearly 2000 times more massive
  than e-)
• Atomic number ( of p) identifies an element
• p and e- have the same magnitude of charge
  (opposite sign)
• When elements lose e-s they become cations (gain
  anions)
• Neutron plays no role in the chemistry of
  elements
• but acts as a cement to hold nucleus
  together
• The force holding nuclear particles (p and no)
  together is the nuclear strong force (only acts
  over extremely short distances)
• For light elements there are nearly s of no
  and p
• The more protons in a nucleus, the larger the
  neutron to proton ratio required to hold nucleus
  together
• no not paired with p will decay into a p and an
  e-
• (this will decrease the no to p ratio)
• For nuclear reactions mass ?
  energy
• (Emc2)

4

• All elements above atomic of 83 or more are
• 3 modes of decay
• Alpha Decay(a - a Helium nucleus 42He, least
  penetrating)
• Beta Decay (ß - an electron o-1e)
• Gamma Decay (? - short ? EM radiation, most
  penetration)

5

• Radioactive Isotopes- same of p different of
  no
• (some more than others)
• Half-Life a way to measure rate of radioactive
  decay
• (time required for half of a sample to decay)
• Transmutation-A nucleus changing into another
  nucleus
• 23892U ? 23490Th 42He 23490Th ? 23491Pa 0-1e
• (the sum of the mass and atomic are conserved
  on each side of the yields arrow)

6

• Artificial Transmutation pg.647-648
• In 1919, Ernest Rutherford bombarded nitrogen
  nuclei with ________ particles from a piece of
  radioactive ore and found traces of oxygen and
  hydrogen were produced.
• 147N 42He ? 178O 11H
• After Rutherfords work, many bombarded elements
  with radioactive particles (later with high speed
  particles in atom-smashing particle
  _______________________).
• Elements beyond _____ of periodic table formed
  by transmutation.
• Carbon Dating pg. 651-652 fig. 33.18
• The earths atmosphere continually bombarded with
  _________ rays (mainly high energy protons).
  Result of bombardments is the transmutation of
  many atoms. Atmospheric protons capture stray
  electrons to become _______________ in the upper
  atmosphere. Neutrons have _____ charge (can
  travel long distances with no interactions with
  other matter).
• The neutrons can __________ with nitrogen
  molecules in lower atmosphere to convert 14N to
  14C
• (14C is a radioactive nuclide). 147N 10n ?
  146C 11H
• Most carbon on earth is 12C a small percentage is
  14C (contained atmospheric CO2).
• Plants take in CO2, living things eat plants, so
  all living things contain some 14C.
• Carbon-14 (a ____ emitter) decays into nitrogen.
  146C ? 147N 0-1e
• When a living thing dies, it stops taking in 14C
  (which will decay at a known rate called _______
  life).
• If analyzed later, the amount of 14C in dead
  material carbon-14 will ___________.
• Compare amount of 14C in a current piece of
  material to the old material of the same size.
  The ratio can be used to ________ the material
  (used to date trees, wooden artifacts, skeletons
  etc).
• Assumptions are made which can yield large
  sources of error.
• Atmosphere remains ____________ in its
  production of 14C (not true due to the changing
  magnetic field of the earth and changing cosmic
  activity of the earth or no microorganisms on the
  materials to add to or take away from the amount
  of 14C).

alpha
accelerators
92
cosmic
no
neutrons
collide
ß
half
decrease
date
constant
7

• Radioactive Tracers pg.649 fig. 33.15
• Radioactive __________ (radioactive isotopes)
  incorporated into compounds can give location of
  the compound over time.
• Once in an organism or material, a detector
  (Geiger counter, scintillation counter, or other
  radioactive probe) can determine the amount of
  that isotope present in different locations.
• Tracers used to study metabolic pathways, blood
  circulation or the amount of a certain fertilizer
  taken up by a plant.
• Automobile engineers test wear (using different
  kind of motor oils) of pistons (make piston wall
  _______________ ). When piston wall wears away
  the radiotracer is gone (gives off no radiation
  from that point on).
• Tracers used to determine location of pipe
  _____________.
• Effects of Radiation on Humans Read pg. 653-655

tracers
radioactive
leaks