Atomic Structure and Nuclear Physics Fundamentals

Fundamental Atomic Definitions

• Atom: The smallest unit of a chemical element that retains its identity and properties, which cannot be split by chemical processes.
• Element: A substance composed of identical atoms.
• Compound: A substance made up of different atoms combined in a specific numerical relationship.

The Bohr Model of the Atom

Taking the Rutherford model as a starting point, Niels Bohr sought to incorporate the phenomena of gas absorption and emission, alongside the new theory of energy quantization developed by Max Planck. The atom is described as a miniature solar system with a nucleus at the center and electrons moving in well-defined orbits.

• Each orbit has an associated energy level; the further the orbit is from the nucleus, the higher its energy.
• Electrons do not radiate energy (light) while they remain in stable orbits.
• Electrons can jump between orbits. If an electron moves to a higher energy level, it absorbs energy equal to the difference between the orbits. If it moves to a lower energy level, it releases energy as radiation (light).

Bohr's greatest success was explaining the emission spectrum of hydrogen. The photon is emitted when an electron transitions between orbits, with the angular momentum radiated as h/2π.

Heisenberg's Uncertainty Principle

This principle states that it is impossible to determine certain pairs of physical variables, such as position and momentum, with arbitrary precision simultaneously. In other words, the greater the certainty in determining the position of a particle, the less certainty there is regarding its momentum.

The Atomic Nucleus

Dimensions and Composition

The majority of an atom's mass is concentrated in the nucleus, which consists of protons and neutrons (collectively known as nucleons). These are approximately 1836 and 1838 times heavier than an electron, respectively. While the volume of an atom is difficult to define due to the diffuse nature of electron clouds, it is estimated at 1.0586x10⁻¹⁰ m (twice the Bohr radius for hydrogen). The hydrogen nucleus is approximately 1x10⁻¹⁵ m, yet it accounts for nearly 100% of the atom's mass.

Radioactive Decay

Radioactive decay is the process by which a nucleus emits radiation, transforming into a different nucleus. Physicists analyze these emissions to understand the internal structure of atomic nuclei.

Nuclear Energy: Fission and Fusion

• Nuclear Fission: A process where a nucleus is struck by a neutron, causing it to split into two smaller nuclei.
• Nuclear Fusion: A process where two nuclei join together to form a more stable, heavier nucleus.
• Nuclear Power Plants: Industrial facilities that generate electricity using nuclear energy. They utilize fissile materials to produce heat through nuclear reactions, which is then converted into electricity via a conventional thermodynamic cycle.