Radioactivity
Isotopes and the Atomic theory
Radioactivity
• The release of high-energy particles and rays
of energy from a substance caused by changes
in the nuclei of the atom
Uses
• Medical diagnostic equipment and treatment,
• Electricity
Natural Background Radiation
• Fast moving particles or waves that are found
in the natural environment
Radiation
• High-energy rays and particles emitted by
radioactive sources
– eg,. Microwave, radio waves, X-rays, Gamma rays
Isotopes and Mass Number
Isotopes: Atoms that have the same number of
protons but different number of neutrons
Eg. Na with 12 neutrons or Na with 11 neutrons
How do we determine if an atom is an
isotope
• We must be able to calculate the number of
neutrons
Remember atomic mass = protons + neutrons
neutrons = atomic mass – atomic number
Representing isotopes
You will need to write a standard atomic symbol:
• Symbol (K)
• Atomic number (19)
• Atomic mass (39)
Eg
39K
19
Writing out names of isotopes
• Write out atom name then a dash and then
the atomic mass given (may be different then
one on the periodic table)
Eg Carbon-12, or Carbon-14
Assignment
Questions 1-4