Fundamentals of Atomic Theory and Nuclear Physics

Atomic Theory

• All matter consists of atoms.
• Atoms of the same element are identical to each other and different from those of other elements.
• Atoms of different elements can combine to form compounds.

Atomic Models

1. Dalton's Atomic Model

Dalton proposed that atoms were indivisible and possessed specific properties.

2. Plum Pudding Model

Thomson discovered the electron, a particle with an electric charge. He proposed that atoms consisted of negative electrons distributed within a sphere of positive charge, rendering the atom electrically neutral.

3. Rutherford Model

Following the discovery of subatomic particles, Rutherford proposed that atoms are composed of protons, neutrons, and electrons. The number of protons and electrons is equal, ensuring electrical neutrality. The mass of protons and neutrons is significant, while the mass of electrons is negligible. Atoms consist of a nucleus containing protons and neutrons, with electrons orbiting around it.

4. Bohr Model

Bohr proposed that electrons are distributed in specific layers or shells around the nucleus, with each layer holding a fixed number of electrons.

Elements

Elements are substances that cannot be decomposed into simpler substances because they consist of a single type of atom.

• Atomic Number (Z): Remains constant.
• Mass Number (A): Can vary.
• Isotopes: Atoms of the same element with different numbers of neutrons.
• Ions: Atoms that have gained or lost electrons, resulting in an electric charge.

Cation

An atom that is positively charged because it has lost electrons.

Anion

An atom that is negatively charged because it has gained electrons.

Radioactivity

In 1896, French physicist A.H. Becquerel discovered that certain compounds emitted radiation capable of exposing photographic plates. Further study revealed that some atoms are unstable and can transform into others. Later, Pierre and Marie Curie discovered radioactive chemical elements. Radioactive substances have unstable nuclei that sporadically break down, releasing energy in the form of particles:

• Alpha particles: Nuclei that are unable to penetrate paper.
• Beta particles: Electrons that can pass through paper but are stopped by aluminum.
• Gamma rays: Waves that pass through paper and aluminum but are stopped by lead.

Nuclear energy is the radiation contained within the core of the atom, representing an enormous amount of energy.