Download 1035239Notes 4.4

Chemical Reactions
• Involves the change of one or more
substances into new substances
• Atoms are rearranged but their
identities do NOT change
• The reaction involves the atom’s
electrons only
Nuclear Reactions
• An atom of one element changes into
an atom of another element
• The identities of the atoms do change
• Involves a change in the atom’s nucleus
• Don’t occur that often in nature
because many atoms have already
decayed (undergone nuclear rxns) into
stable atoms during Earth’s long history
Radioactivity
• Some substances spontaneously emit
radiation – it requires no energy
• Occurs because an atom’s nucleus is unstable
or overcrowded
• The atom gains stability by losing energy or
emitting radiation (like a pencil tipping over)
• An atom continues to be radioactive and
undergoes decay until its nucleus becomes
stable
Radioactive Decay
• 3 main types of radiation are emitted during
radioactive decay (alpha, beta & gamma) –
all 3 have energy & 1 has mass
• The rays & particles emitted are known as
RADIATION
• The process of emitting them is radioactivity
or radioactive decay
Nuclear Stability
• The prime factor in achieving nuclear
stability is for an atom to have a
favorable neutron to proton ratio in its
nucleus
• Too high or too low leads to instability
and nuclear decay
Alpha Radiation
• Radiation made up of alpha particles
• Each particle has 2 p+ and 2 no, so has
a +2 charge and a mass of 4 amu
• Basically a helium atom without
electrons
• The biggest and slowest of the three
types, so it penetrates into matter the
least
Beta Radiation
• Consists of the fast moving electrons
called beta particles
• Has no mass but has a -1 charge
• Smaller with more energy than alpha
particles, so penetrate further
• A beta particle breaks off of a neutron
and leaves behind a proton
Gamma Radiation
• It’s high energy radiation that has no mass,
and no electrical charge
• Highest energy of the 3, so penetrates the
most & potentially the most damaging
• Accounts for most of the energy lost during
radioactive decay
• Emission of gamma rays alone does not
result in a new atom but usually
accompanies beta & alpha radiation
Nuclear Equation
• An equation that shows what happens
during a nuclear reaction
• Both the mass number and atomic
number is conserved
• Examples:
Polonium-210 undergoes alpha decay
Nuclear Equation
• Both the mass number and atomic
number is conserved
• Examples:
Thorium-234 undergoes beta decay
Nuclear Equation
• Both the mass number and atomic
number is conserved
• Examples:
Uranium-234 undergoes alpha decay
Nuclear Equation
• Both the mass number and atomic
number is conserved
• Examples:
Bismuth-214 undergoes beta decay
Nuclear Equation
• Both the mass number and atomic
number is conserved
• Examples:
Uranium-238 undergoes alpha decay
accompanied by 2 gamma rays
Did you know?
• Radon exists only as a by-product of the
radioactive decay of uranium-238.
• Radon will further decay into radioactive
isotopes of polonium, bismuth and lead.
• All 3 of these isotopes are heavy metals that
are difficult to remove from the human body.
• It’s estimated 10,000 to 20,000 lung cancer
deaths per year are caused by exposure to
radon.
• Radon is usually found in soil or building
materials.