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7.1 Atomic Theory and Radioactive Decay
 Natural background radiation exists all around us.
 ____________________ is the release of high energy particles or waves.
- When atoms lose high energy particles and waves, ________________ can be formed.
– Radiation is useful (medical scans & cancer treatment) but it damages DNA in cells.
The Electromagnetic Spectrum
Isotopes
 are different atoms of the same element, with a different number of __________ in the nucleus.
– changing the # of ____________ changes the _____________ number
 Remember: mass # = ________________________________
– isotopes still have the same __________________________________
Atomic Mass (the decimal #’s)
 Atomic mass = ___________________________________________________.
Representing Isotopes
 Isotopes are written using standard atomic notation.
– Chemical symbol + atomic number + mass number.
– Potassium has three isotopes,
Radioactive Decay
 Can result in new __________ forming.
– Radioactivity results from having an _____________ ____________.
– Radioactive decay = when nuclei break apart + release ___________ from the nucleus as
__________________.
 Radioactive decay continues until a _________ element forms.
 An element may have only certain isotopes that are radioactive called
____________________
Uranium goes through many decay steps before it becomes stable.
 Rutherford identified three types of radiation using an electric field.
– Positive _____________________ were attracted to the negative plate.
– Negative ____________________ were attracted to the positive plate.
– Neutral _____________________ did not move towards any plate.
A) Alpha Radiation:
 is a stream of alpha particles, (shown as )
– _______________________
– the most massive of the 3 types and are the equal to a Helium nucleus.
– Alpha particles are represented by the symbols:
 2 protons and 2 neutrons make a mass number of 4
 it has a charge of 2+ because of the protons
Alpha particles are ____________ and penetrate materials much less than the other forms of radiation. A sheet
of paper will stop an alpha particle.
 The release of alpha particles is called _____________ _____________.
 Example: the alpha decay of Radium – 226

B) Beta Radiation:
 A Beta particle, ________ is a _________ ____________ _______________.
– _____________ charged, and are _________ massive than alpha particles.
– Beta particles are represented by the symbols :



electrons are very tiny, so beta particles are assigned a mass of __.
one electron gives a beta particle has a charge of ___________.
Beta decay occurs when a neutron changes into a _________ + an ___________.
 The proton stays in the ___________, and the electron is _____________.
Example: The beta decay of iodine - 131
 It takes a thin sheet of aluminum foil to stop a beta particle.
C) Gamma Radiation:
 Gamma radiation, ___, is a ray of _________ energy, short-wavelength radiation.
– has ____ charge and _____ mass.
– is the _____________ energy form of electromagnetic radiation.
– It takes thick blocks of lead or concrete to stop gamma rays.
– Gamma decay results from ____________ being released from a high-energy
________________.
 Often, other kinds of radioactive decay will also release gamma radiation.
– Uranium-238 decays into an alpha particle and also releases gamma rays.
Nuclear Equations:
 are written like chemical equations, but represent ___________ in the ___________ of atoms.
– Chemical equations represent changes in the position of atoms, not changes to the atoms
themselves.
 Remember:
– The sum of the ________ ___________ on each side of the equation should equal.
– The sum of the __________ on each side of the equation should equal.