Atoms and Isotopes

1
Atoms and Isotopes

• What are atoms, isotopes, and radioactive decay?

2
Atoms and Subatomic Particles

• Atoms are the smallest unit of a chemical element
  that has all the chemical properties of that
  element.
• Made up of
• Protons positive charge
• Neutronsno charge
• Electronsnegative charge

3
The Periodic Table of the Elements
4
Reading Atomic Notations

• Z is the atomic (proton) number
• N is the neutron number
• A is the mass number (NZ)
• X is the chemical element symbol

5
Isotopes

• Atoms of one element may have different number of
  neutrons the different possible versions of each
  element are called isotopes.
• Isotopes of one element all have the same number
  of protons (atomic number, Z) but different
  numbers of neutrons (thus different atomic
  weights, A).
• Every element has several isotopes
• All isotopes are shown on the chart of the
  nuclides.

6
Radioactive Decay

• Unstable atoms will spontaneously transform until
  they reach a stable configuration.
• These transformations are accompanied by releases
  of energy.

7
Radioactive Decay

• This energy, given off in waves from an atom, is
  known as radiation.
• Substances that give off radiation are called
  radioactive.
• The process of isotopes emitting particles and
  energy to become more stable is called
  radioactive decay.

8
Radioactive Decay

• Main types of radioactive decay
• Alpha emission
• Beta emission
• Positron emission
• Gamma emission

9
Radioactive Decay

• Alpha emission (a)
• Nucleus emits an alpha particletwo protons and
  two neutrons
• Equivalent to a helium nucleus (He).
• Alpha Decay Animation http//ie.lbl.gov/education/
  glossary/AnimatedDecays/AlphaDecay.html

10
Radioactive Decay

• Beta Emission (ß)
• Nucleus emits an electron, and a neutron is
  converted to a proton.
• Beta Decay Animations http//ie.lbl.gov/education
  /glossary/AnimatedDecays/Beta-Decay.html

11
Radioactive Decay

• Positron Emission
• Nucleus emits a positron (identical to an
  electron in mass, but has a positive charge)
• Positron is formed when a proton converts to a
  neutron.

12
Radioactive Decay

• Gamma emission (?)
• Nuclei seeking lower energy states emit
  electromagnetic radiation, which is in the gamma
  ray region of the electromagnetic spectrum.
• Rays are emitted in conjunction with another type
  of decay (alpha or beta).
• Gamma Decay http//ie.lbl.gov/education/glossary/A
  nimatedDecays/GammaDecay.html
• Additional animations http//ie.lbl.gov/education
  /glossary/Glossary.htm

13
Radioactive Decay Chains
14
Half Life

• The amount of time it takes for half of the atoms
  of a given isotope to decay to another form is
  known as its half-life.
• The value can be from fractions of a second to
  billions of years.

15
Half Life

• Half-life values are constant.
• There is no way to speed up or slow down this
  natural process.
• Cannot predict when a specific atom will decay.
• Can predict the number of atoms that will decay
  in a certain time period.

16
Half Life of Uranium-235