Transcript Unit 2 Part 2: Nuclear Chemistry

Unit 2 Part 2: Nuclear Chemistry
1st, 3rd, and 4th Periods
Nuclear Chemistry
• Nuclear chemistry is the study of
the structure of atomic nuclei
and the changes they undergo.
• Why would the nucleus want to
undergo a change?
• TO BECOME MORE STABLE &
HAVE LESS ENERGY!!!
Radioactivity – The Beginning
• In 1896, Antoine Becquerel and his
graduate students, Marie and Pierre
Curie, discover radioactivity
• They used Uranium salts which were
placed next to film plates. When opened,
the plates were found to be developed.
•The Curies showed that uranium
gave off rays that caused the plates
to become exposed
•Rays were called radioactivity
•The three won a Nobel Prize for
their work
Relation to Dalton
•This work was a deathblow to the
theory of an indivisible atom
•Radioactive isotopes have
unstable nuclei that overtime
transform to a stable nonradioactive nucleus
Radioactive Decay
•Radioactive Decay-process in which
an unstable nucleus loses energy by
emitting radiation
•Three types of radiation are
produced: alpha, beta and gamma
particles
Alpha Radiation ()
•Helium nuclei emitted from a radioactive
source
•Alpha particles- two protons and two
neutrons; double positive charge
•Written as 42He
Safety Concerns
•Because of large mass and charge,
these are not very penetrating
•Can be stopped by a sheet of paper
or even dead skin cells
•Harmful if ingested
Alpha Particle
•Loss of alpha particle lowers atomic
number by two and mass number by
four
•Ex: Uranium-238 decays to Thorium234 and an alpha particle
• 238 92U  234 90Th + 42He
Beta Radiation (  )
•Formed by the decomposition of a
neutron of an atom
1
1
0
• 0n  1H + –1e
•Beta particles- fast moving electrons
Safety Concerns
•Contain half the charge and are much
lighter than alpha particle
•Much more penetrating
•Can be stopped by aluminum foil or
thin pieces of wood
Beta Particles
•Written as 0–1e or 0–1 
•The proton stays in the nucleus and
the electron is ejected from the
atom
•Ex: Carbon-14 decays to Nitrogen-14
and a beta particle
14
14
0
• 6C  7N + –1e
Gamma Radiation (  )
•Electromagnetic (EM) Radiation
•Visible light is also EM radiation,
but at a much lower energy
•Often emitted by the nuclei of
disintegrating radioactive atoms
along with alpha and beta radiation
Gamma Rays
•No mass and no electrical charge
•Does not alter atomic number or the
mass number of an atom
•This type of radiation only releases
energy from the nucleus
•Symbol:  (gamma)
X-Rays
•X-Rays are NOT emitted during
radioactive decay
•Produced when excited electrons in
certain metals lose their energy
• Except for their origins, gamma and xrays are essentially the same
• Both rays pass easily through paper,
wood, and the human body
• Can be mostly stopped by several meters
of concrete or several centimeters of lead
Nuclear Equations
• Other Particles:
•Positron: a positively charged
electron; 0+1e or 0+1
•Neutron: 10n0
•Proton: 11p+ or 11H+