Radioactivity The Nucleus Isotopes Radioactivity Three kinds of emission Nuclear Processes

Rutherford’s Experiment

Results of the Experiment Most of the particles were undeviated Some particles were deviated at angles less than 90⁰ Only a few particles were deviated at angles more than 90⁰

Meaning of Results Atom is mostly empty space Most of its mass is concentrated at the nucleus The nucleus is very small

The Atom The nucleus Protons Neutrons The number of protons = number of electrons = atomic number, Z While the number of protons + neutrons = atomic mass, A

Isotopes Have the same atomic number but different atomic mass A.k.a. nuclide

Radionuclide Some isotopes Are unstable Too many nucleons Too much energy Have spontaneous nuclear decay Emit energetic particles or rays The phenomenon of their decay is known as radioactivity

Nature of Radioactivity

Nature of Radioactivity Random There is a constant probability of decay of the nucleus of an atom Spontaneous Decay is not affected by environmental factors like temperature and pressure.

Graph of Radioactive Decay Count rate is decreasing with time Random Fluctuations in the graph Graph is not a smooth curve