Atomic Theory and Models

History of the Atom

• The plum pudding model described an atom as a sphere of positive charge with negatively charged particles (electrons) dispersed throughout.
• The modern atomic model depicts a nucleus at the atom's center, containing protons and neutrons, and most of the atom's mass. Electrons orbit the nucleus at different energy levels.

Rutherford's Alpha Scattering Experiment

• Alpha particles were directed at a thin gold foil.
• Most alpha particles passed straight through the foil.
• Some particles were deflected at small angles.
• A small fraction of alpha particles were deflected back towards the source.
• This experiment disproved the plum pudding model.
• The results indicated the atom is primarily empty space with a small, dense, positively charged nucleus.

Isotopes

• Isotopes are varieties of the same element having the same number of protons but differing numbers of neutrons.
• The varying number of neutrons alters the mass number of the isotope.
• The charge remains the same because neutrons have no charge.

Ions

• Ions are atoms lacking a balance of protons and electrons, having different numbers of negatively charged electrons.
• The number of protons remains consistent with the neutral atom, determining the atomic number and the element.
• The differing number of electrons changes the overall charge of the ion.
• The mass of an atom remains largely unchanged due to the negligible mass of electrons.

Radiation

• Alpha radiation is released from the nucleus when an alpha particle (consisting of two protons and two neutrons) is emitted.
• Alpha radiation is highly ionizing, travels a short distance in air (a few centimeters), and is stopped by a sheet of paper. Alpha radiation is used in smoke detectors.
• Beta radiation is emitted from the nucleus when a high-speed electron (beta particle) is released.
• Beta radiation is moderately ionizing, travels further in air (a few meters), and is stopped by aluminum. Beta radiation is utilized in material thickness gauges.
• Gamma radiation involves the emission of electromagnetic waves (gamma rays) from the nucleus, and are not particles.
• Gamma radiation is weakly ionizing, travels long distances in air (up to several kilometers), and is absorbed by lead or thick concrete. Gamma radiation is used for sterilization of medical equipment.

Alpha Radiation

• It is highly ionizing, leading to significant cellular damage.
• Its range in air is relatively short (a few centimeters), easily stopped by paper.
• Alpha radiation is used in smoke detectors.

Beta Radiation

• It is moderately ionizing.
• Beta particles travel further in air (a few meters) and are stopped by aluminum.
• Beta radiation is used in material thickness gauges.

Gamma Radiation

• It is weakly ionizing.
• Gamma rays have a very long range in air (up to several kilometers) and are absorbed primarily by lead or thick concrete.
• Gamma radiation is used in sterilizing medical equipment.

Half-Life

• Half-life is the time required for half of the radioactive nuclei in a sample to decay.
• Radioactive decay is a random process.
• Activity refers to the rate of radioactive decay and is measured in Becquerels (Bq).

Radiation Risks

• Irradiation is exposure to radiation.
• Irradiation is minimized by keeping radioactive sources in lead-lined containers.
• Beta and gamma radiation present greater irradiation risks due to their ability to penetrate skin.
• Contamination involves radioactive particles on objects or surfaces.
• Contamination prevention includes personal protective equipment (PPE) like gloves or protective suits.
• Alpha radiation presents a greater contamination risk due to its high ionizing potential.