Atomic Structure and Subatomic Particles Quiz

Atomic Structure

• Atoms are composed of a positively charged nucleus surrounded by negatively charged electrons.
• The nucleus contains protons (positive charge) and neutrons (neutral charge).
• Electrons have negligible mass compared to protons and neutrons.
• The typical radius of an atom is 1 × 10⁻¹⁰ meters.
• The radius of the nucleus is significantly smaller, approximately 10,000 times smaller than the atom's radius.

Subatomic Particles

• Proton: Relative mass of 1, relative charge of +1.
• Neutron: Relative mass of 1, relative charge of 0.
• Electron: Relative mass of 0 (or 0.0005), relative charge of -1.

Isotopes

• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
• They have the same atomic number (number of protons) but different mass numbers (sum of protons and neutrons).
• Examples include Carbon-12, Carbon-13, and Carbon-14.

Electron Arrangement

• Electrons exist in different energy levels, or shells, around the nucleus.
• Electron arrangements in atoms may change with the interaction of electromagnetic radiation.
• The number of electrons is equal to the number of protons in a neutral atom.

Atoms and Electromagnetic Radiation

• When electrons transition from higher to lower energy levels, they emit electromagnetic radiation.
• When electrons transition from lower to higher energy levels, they absorb electromagnetic radiation.
• Electrons can completely leave the atom if they absorb sufficient energy, leading to the formation of a positively charged ion.

Atomic Models

• Dalton's Model: Atoms are indivisible spheres.
• Thomson's Model (Plum Pudding): Atoms have a positive sphere with negatively charged electrons embedded.
• Rutherford's Model: Most of the atom is empty space, with a dense, positive nucleus at the center and electrons orbiting it.
• Bohr's Model: Electrons exist in specific energy levels (orbits) around the nucleus.

Radioactive Decay

• Radioactive decay is the spontaneous process where unstable atomic nuclei emit radiation as they transform into more stable forms.
• Activity is the rate at which radioactive nuclei decay.
• Count rate is the rate at which particles are detected.
• Decay can be measured in Becquerels (Bq).

Types of Radioactive Decay

• Alpha decay: Emission of an alpha particle (helium nucleus).

• Beta decay: Emission of a beta particle (electron or positron).

• Gamma decay: Emission of a gamma ray.

• Each type of decay affects the mass and/or charge of the nucleus differently.

Half-Life

• Half-life is the time required for half of the radioactive nuclei in a sample to decay.
• Half-lives are constant and used to predict the rate of decay in large samples of radioactive material.
• Half-lives can range from fractions of a second to billions of years depending on the isotope.

Contamination vs. Irradiation

• Contamination involves the presence of radioactive material on an object, meaning the material is radioactive.
• Irradiation involves the exposure of an object to radiation but does not make it radioactive.

Background Radiation

• Background radiation is weak radiation from natural sources such as cosmic rays and rocks.
• Measurement of radiation dose is in Sieverts (Sv).

Nuclear Fission

• In nuclear fission, a large, unstable nucleus is split into smaller nuclei, releasing energy.
• A neutron triggers the initial splitting process and produces more neutrons, leading to a chain reaction (e.g. nuclear bomb).
• Fission is useful for generating energy in power plants.

Nuclear Fusion

• In nuclear fusion, small nuclei combine to form a larger, more stable nucleus, releasing enormous amounts of energy.
• The source of energy from the sun is fusion.
• Fusion is a potentially more efficient energy source than fission, but practical methods for controlling fusion reactions are not yet developed.

Uses of Radioactive Substances

• Tracers (like Technetium-99m): Used in medicine to follow the passage of substances through the body.
• Chemotherapy: Uses gamma rays to damage cancer cells.