Transcript Unit 3 – Atomic Structure

Unit 2 – Atomic
Structure & Nuclear
Chemistry
Part II – Nuclear Chemistry
Part II Key Terms
• Alpha decay – spontaneous decay of a nucleus that emits a helium nucleus and
energy
• Beta decay – spontaneous decay of a nucleus that emits an electron and energy
• Gamma decay – spontaneous decay of a nucleus that emits
• Isotope -Atoms of the same element with different numbers of neutrons
• Mass number -The total number of protons and neutrons in a nucleus
• Subatomic particles -The three kinds of particles that make up atoms: protons,
neutrons, and electrons.
• Nuclear fission - Splitting of the nucleus into smaller nuclei
• Nuclear fusion - Combining nuclei of light elements into a larger nucleus
• Nucleon - a constituent (proton or neutron) of an atomic nucleus
• Radioactive decay - Spontaneous release of radiation to produce a more stable
nucleus
• Radioactive isotope - An isotope (an atomic form of a chemical element) that is
unstable; the nucleus decays spontaneously, giving off detectable particles and
energy
Nuclear Reactions
 All nuclear reactions are based on Einstein’s Theory of
Relativity
 At speeds approaching the speed of light, energy and mass
are interchangeable
 E = mc2
Energy = mass x (speed of light)2
 Mass can be converted to energy and vice versa
Mass Defect
 There is a difference between the mass of an atom and the
various particles that make up the atom
 This difference is called the mass defect of the atom
 This mass defect is the binding energy of the atom
 In nuclear reactions, the binding energy is released as energy
(heat, light, or gamma radiation) and/or particles with
measureable mass
Types of Nuclear Reactions
• Fission – Splitting of the nucleus into smaller nuclei
• Fusion – Combining nuclei of light elements into a larger
nucleus
• Radioactive Decay – Spontaneous release of radiation to
produce a more stable nucleus
Fission
 Nucleus splits into smaller nuclei when struck by a neutron of
sufficient energy
 Tremendous release of energy
 When controlled can produce huge amounts of power in nuclear
reactors
 Naturally occurs in uranium and other ores in spontaneous fission
 Clean source of energy with no carbon footprint
 Produces radioactive nuclear waste with long term environmental
and health considerations
Fission Process
Fission and Nuclear Reactors
Fusion
 Lighter nuclei (such as hydrogen) combined to form heavier
nuclei
 Tremendous release of energy

2H
+
Deuterium

Tritium
3H
4He
+
1n
+ energy
Helium
(occurs naturally in water)
 Powers the sun and stars
 No practical application to produce usable energy at this time
Fusion Process
Radioactive Decay
• Spontaneous release of radiation by unstable nuclei in order to
increase stability
• Radiation can be either energy alone (gamma) or energy
accompanied by release of a particle (all of the other forms of
decay)
Forms of Radioactive Decay
 Alpha decay – release of alpha particle and energy
 Beta decay – release of beta particle and energy
 Gamma Emission – release of electromagnetic
radiation (energy)
 Positron Emission – release of a positron and energy
 Electron Capture – absorption of and electron and release of energy
 Neutron Emission – release of a free neutron and energy
Alpha Decay
 Typically found in heavier nuclei and the means to achieve stability
is to reduce mass
 Nuclei shed mass in the form of a helium nucleus to become more
stable
 Helium nucleus that is released is ionized and called and Alpha
Particle
Alpha Decay (cont.)
 Alpha Particle is positively charged (no electrons present)
 Alpha Particles are very massive, but travel slower (low penetrating
power)
 Can cause significant tissue damage if not shielded
 Shielding can be accomplished with clothing or paper
Alpha Decay Process
Beta Decay
 Common in nuclei of any size where instability is caused by the number
of neutrons
 Neutron decays into a proton and an electron
 Proton remains in the nucleus
 The electron leaves the atom and is called a Beta Particle
Beta Decay (cont.)
 Beta Particle is negatively charged
 Mass of the nucleus is unchanged
 Beta particles have very low mass but are travelling at very high
speed
 Beta particles can penetrate through the skin and cause deep tissue
damage
Beta Decay Process
Gamma Radiation
 Nucleus becomes more stable through the release of
electromagnetic energy
 No change in mass
 No change in the element
 The Gamma radiation can be reduced by shielding, but Gamma
radiation cannot be stopped
 Usually found with another type of decay, but not always
Radioactivity Decay Comparison
Radioactive
Decay Type
Mass
Charge
Penetrating
Power
Transmutation
Alpha
4 amu
Positive
Low
New Element
Formed
Beta
0 amu
Negative
High
New Element
Formed
Gamma
None
(no particle)
None
Extremely High
No
Nuclear Reaction
Mass Conservation
• All nuclear reactions must conserve the overall mass of the
particles involved in the reaction
• Two properties must be the same on both sides of a nuclear
equation
• Total Mass Number – the sum of the mass numbers of all
particles must be the same on both sides of the reaction
• Total Atomic Number – the sum of the atomic numbers of all
particles must be the same on both sides of the reaction