History of the Atom

Study Notes

History of the Atom

The plum pudding model describes an atom as a positively charged sphere, containing negatively charged particles embedded throughout.
The current model depicts the atom with a nucleus at its center, containing protons and neutrons, and negatively charged electrons orbiting the nucleus at different energy levels.
The majority of an atom is empty space.
Most particles passed straight through the gold foil. Some were deflected slightly, while a very few were deflected back significantly.
The nucleus is mainly made of protons and neutrons, with a relative mass of 1 compared to the electron.

Ernest Rutherford's Alpha Scattering Experiment

The alpha scattering experiment was conducted to investigate the structure of the atom.
Alpha particles were emitted from a source and directed towards a thin sheet of gold foil.
The results of the experiment led to the conclusion that atoms are mostly empty space.
The experiment also suggested the presence of a small, dense, positively charged nucleus.
The experiment disproved the Plum Pudding Model.

Isotopes and Ions

Isotopes are atoms of the same element with the same number of protons but a different number of neutrons.
The mass number will change depending on the number of neutrons, but the atomic number (number of protons) will remain the same.
Ions are atoms with the same number of protons but a different number of electrons.
The mass number of an ion does not change because the mass of an electron is negligible.
Gaining or losing electrons causes a change in charge.

Radiation

Alpha radiation is the emission of an alpha particle from the nucleus.
Alpha particles are strongly ionizing, meaning they can damage cells and materials.
Alpha radiation has a short range in air and can be stopped by a sheet of paper.
Beta radiation is the emission of a high-speed electron from the nucleus.
Beta particles are moderately ionizing and have a longer range in air than alpha particles.
Beta radiation can be stopped by a sheet of aluminum.
Gamma radiation is the emission of electromagnetic waves from the nucleus.
Gamma rays are weakly ionizing and travel far distances in air.
Gamma radiation can be stopped by thick layers of lead or concrete.

Half-Life

Half-life is the time taken for the number of radioactive nuclei in a sample to decrease by half.
Radioactive decay is a random process, meaning it is impossible to predict which nucleus will decay next.
The rate at which a radioactive source decays is called its activity.
The half-life of a radioactive substance varies depending on the element.

Radiation Risks

Irradiation is exposure to radiation.
Irradiation can be reduced by keeping sources of radiation in lead-lined boxes.
Beta and gamma radiation pose the greatest risk of irradiation because they can penetrate the skin.
Contamination occurs when radioactive particles get onto objects, surfaces, or living organisms.
Contamination can be prevented by wearing appropriate personal protective equipment (PPE), such as gloves and special suits.
Alpha radiation poses the biggest risk of contamination due to its strong ionizing ability within a localized area.

Description

Explore the evolution of atomic theory from the plum pudding model to Rutherford's alpha scattering experiment. Understand how these discoveries shaped our current understanding of the atom's structure and the concept of empty space within it.