Nuclear Chemistry

1
Nuclear Chemistry

• Stability
• And
• Radioactivity

2
A Brief Review

• The protons and neutrons are contained in the
  ___________, the electrons move around outside
  the nucleus.
• The number of ______________ determines the
  identity of the atom.
• During a ________________ reaction, there are no
  changes to the nucleus, so the atom retains its
  identity.

3
Nuclear Reactions

• Reactions which involve a change in an atoms
  nucleus are called _____________________________.
• In the late 1890s, scientists noticed that some
  elements spontaneously emit ________________ in a
  process called _______________________.

4
The Scientists of Nuclear Chemistry

• ________________________ 1895 discovered
  x-rays as high energy emissions that caused
  photographic plates to darken
• _______________________ around same time
  discovered uranium salts that also caused
  photographic plates to darken
• _______________________ around 1900
  established the origin of radioactivity and
  identified 2 new elements, polonium and radium

5
Nuclear Stability

• The stability of a nucleus can be shown by its
  ______________________ (n/p ratio)
• For atoms with _______ atomic numbers (lt20), the
  most stable nuclei are those with n/p ratios of
  11.
• For larger atoms, the most stable nuclei are
  those with n/p ratios within 1.51

6
Nuclear Stability and Radioactivity

• Nuclei that are unstable will undergo some sort
  of ____________________ in order to gain
  stability
• There are several different kinds of decay that
  are possible

7
Beta decay

• Some atoms are unstable because they have too
  high of an n/p ratio (i.e., too many neutrons
  compared to protons)
• These elements undergo _______________
• This does not happen often
• Decreases the number of neutrons and increases
  the number of protons (decreases the n/p ratio)
• In simplest terms, a proton and an electron are
  created from a neutron ? the electron is emitted
  and the proton remains behind.

8
Beta decay (contd)

• Carbon-14 has an n/p ratio of 1.331, which is
  too high
• It decays into ___________________ (7 protons, 7
  neutrons and an n/p ratio of 11)
• 146C ? 147N 0-1ß

9
Alpha Decay

• All nuclei with more than _____ protons are
  radioactive and decay spontaneously
• Both the number of neutrons and the number of
  protons must be reduced in order to make these
  radioisotopes stable
• _____________________ involves the emission of
  alpha particles, which happen to be the same as a
  helium nucleus (2 protons, 2 neutrons)

10
Alpha Decay (contd)

• Polonium-210 will spontaneously decay by alpha
  emission
• 21084Po ? 20682Pb 42He

11
Gamma Radiation

• ________________________ are high-energy
  radiation that possess no mass and are denoted by
  the symbol 00?
• Gamma radiation often occurs with alpha and beta
  radiation, and account for most of the energy
  lost during radioactive decay process
• They are not deflected by electric or magnetic
  fields and can basically travel through anything

12
Gamma Radiation (contd)

• Gamma rays accompany the alpha decay of
  uranium-238.
• 23892U ? 23490Th 42He 200?

13
Positron Emission

• A ________________ is a particle with the same
  mass as an electron, but opposite charge and is
  shown with the symbol 01ß
• During positron emission, a proton in the nucleus
  is converted into a neutron and a positron, and
  then the positron is emitted
• 11p ? 10n 01ß

14
Electron Capture

• _______________________ occurs when the nucleus
  of an atom draws in a surrounding electron
  (usually from the ______________ energy level)
• The electron combines with a proton to form a
  neutron
• 11p 0-1e ? 10n

15
Nuclear Fission

• Atoms with mass numbers greater than ______ tend
  to be less stable and will fragment into smaller
  atoms to increase their stability
• The splitting of a nucleus into fragments is
  called _______________________.
• The fission of a nucleus is accompanied by a very
  _____________ release of energy.

16
Nuclear Fusion

• Lighter atoms (less than mass number 60) may
  ______________ to form a single, more stable
  nucleus
• The combining of atomic nuclei is called
  ________________________.
• Nuclear fusion reactions are capable of releasing
  very large amounts of energy
• Example In the _________, hydrogen atoms fuse
  together to form helium atoms