NUCLEAR CHEMISTRY
Chapter 10
Chemical Rxn vs. Nuclear Rxn
• Chemical reactions involve valence ELECTRONS
• Nuclear reactions involve PROTONS and NEUTRONS
Chemical Energy
• Energy stored in the chemical bonds of a substance
• Chemical reactions involve the breaking of chemical
bonds in the reactants and the formation of chemical
bonds in the products
• During this process, energy is either released (exothermic) or
absorbed (endothermic)
Radioactivity
• The process in which an unstable atomic nucleus emits
charged particles and energy
• An atom that has an unstable nucleus is called a
Radioactive isotope, or Radioisotope
• Carbon-14 is an example of a radioisotope
• Radioisotopes spontaneously change in to other isotopes
over time
• This is called NUCLEAR DECAY and can result in the formation of
an entirely different element than the original element
Historical Figures Jigsaw
• What important discovery was made by Wilhelm Roentgen?
• What material did Antoine Becquerel work with in his own
investigations of X rays?
• What did Becquerel discover through his experiments?
• What two elements were discovered by Marie and Pierre
Curie?
• Why is Ernest Rutherford considered the father of nuclear
physics? List Rutherford's major achievements.
Radioactivity (The Good, The Bad)
• Safari Montage
Nuclear Force
• The attractive force that binds protons and neutrons
together in the nucleus
• Extremely weak at most distances, BUT over the very
short distances present in an atom’s nucleus, the nuclear
force is greater than the repulsive electrical force among
protons
• When the attractive nuclear force and the repulsive
electrical force are not balanced, the nucleus of the atom
is UNSTABLE
How does a nucleus become stable?
• Through radioactive (or nuclear) decay!
• Radiation is emitted from the unstable nucleus in the
form of fast-moving particles and energy
• This results in new nucleus and thus the identity of the
element changes
• Atoms that have an unstable nucleus are called
radioactive isotopes
Nuclear Radiation
• Charged particles and energy that are emitted from the
nuclei of a radioactive isotope
• Types
• Alpha Particles – Least penetrating, travel only a few centimeters
in air, can be stopped by clothes or a sheet of paper
• Beta Particles – More penetrating than alpha particles, pass
through paper, stopped by thin sheet of metal
• Gamma Radiation – Much more penetrating than alpha and beta
particles, need several centimeters of lead or several meters of
concrete to stop gamma radiation
Alpha Decay
• Alpha Particle
• Positively charged particle made up of two protons and two
neutrons
• Has a charge of +2
• QUESTION: If an alpha particle has two protons, which element
does is resemble?
Alpha Decay
• Alpha particles are represented by
• This type of nuclear reaction can be expressed as an
equation (write in the parts of the equation below):
Beta Particles
• An electron emitted by an unstable nucleus
• Has a mass number of (0) and a charge of (-1)
Beta Decay
• During Beta Decay, ONE neutron decays into ONE proton
and ONE electron
• The PROTON stays trapped in the nucleus and the ELECTRON is
released
• What does this mean?
• The product isotope has ONE proton more and one neutron fewer
than the reactant isotope, but the mass numbers are the same
because electrons have NO mass.
Gamma Radiation
• A penetrating ray of energy emitted by an unstable
nucleus
• Has no mass and no charge
• Travel through space at the speed of light
• Can easily pass through the human body
Ionizations
• The process of stripping, knocking off or otherwise
removing electrons from their orbital paths
• This creates free negatively-charged electrons and leaves
nuclei that have a positive charge
• These particles can interact with other materials to
produce changes in materials (like our body)
• If this happens in our cells, cellular damage may result
Nuclear Power
• How it Works
• Chernobyl Disaster
Sources of Radiation
• Background Radiation
• Nuclear radiation that occurs naturally in the environment
• Examples: Air, water, rocks, plants, animals, cosmic rays
• Cosmic rays
• Streams of charged particles from outer space
• Nuclear Radiation in the body
• Because particles and energy can ionize cells in the human body, they can
break apart the bonds holding DNA and proteins together
• If these molecules change, cells may no longer function how they are supposed to
• Radon Gas
• Emits alpha particles, can cause lung cancer
• Formed through a series of nuclear decays that begins with uranium-238 deep
underground
• Radon gas seeps upwards and can accumulate in basements that don’t have
proper ventilation
Geiger Counters
• Used to detect nuclear radiation
• Uses a gas-filled tube to measure ionizing radiation
• Nuclear radiation enters tube, the gas in the tube is
ionized and generates an electric current, which can be
measured
• More nuclear radiation = greater electrical current
Group Discussion
• What is nuclear decay?
• What is emitted from a radioactive isotope during
radioactive decay?
Half-life
• Nuclear Decay Rate
• Refers to how fast nuclear changes take place in a radioactive
substance
• Constant for a given radioactive isotope
• The length of time necessary for half of the atoms of a
sample material to decay
• Half of the atoms have decayed, half remain the same
• Range from fractions of a second to billions of years for
long-lived materials
Radiocarbon Dating
• http://www.youtube.com/watch?v=phZeE7Att_s
• The age of an object is determined by comparing the object’s
carbon-14 levels with carbon-14 levels in the atmosphere
• Used to date fossils up to 50,000 years old
• Why does this work?
• Plants absorb carbon dioxide from the atmosphere during
photosynthesis
• While alive, they maintain the same ratio of Carbon-14 to Carbon 12
as in the atmosphere
• Animals have the same ratio of C-14 to C-12 as the plants they eat
• Once a plant or animal dies, it no longer absorbs carbon and so the
remaining C-14 begins to decay