Atomic Structure: Models, Particles, and Quantum Theory

Fundamental Particles

Electron: It has a mass equal to 9.1 × 10⁻²⁸ grams (0.00055 amu) and an electric charge of 1.6 × 10⁻¹⁹ coulombs.

Proton: It has a mass of 1.67 × 10⁻²⁶ grams (1.00732 amu) and an electric charge of 1.6 × 10⁻¹⁹ coulombs.

Radioactivity and Radiation Types

• Alpha rays: These are made up of particles with a positive electric charge that move at a speed between 16,000 and 32,000 km/s; they are not very penetrating.
• Beta rays: These are formed by electrons with a negative electric charge that move at high speed and are more penetrating than alpha rays.
• Gamma rays: These are not particles but high-frequency electromagnetic radiation that moves at very high speed; they show no electrical charge and have great penetrating power.

The Rutherford Model

Rutherford proposed the following model:

1. The atom consists of a central nucleus with a positive charge, surrounded by negative electrons.
2. The core is very small relative to the total diameter of the atom but contains most of the atomic mass.
3. The electrons orbit the nucleus without colliding with it, at varying distances not exceeding a certain diameter.
4. The number of electrons is sufficient to compensate for the positive charge of the nucleus, so the atom as a whole is neutral.
5. The electrons have a negligible mass relative to the total mass of the atom.

The Bohr Model

The interpretation of atomic spectra allowed Bohr to propose that electrons orbit the nucleus in defined orbits or energy levels.

Atomic and Mass Numbers

The Atomic Number: Each chemical element has a given number of protons in the nucleus, which is peculiar and characteristic.

The Mass Number: This equals the sum of the number of protons and neutrons that an atom has at its core.

Isotopes and Ions

Isotopes: These are atoms that have an equal number of protons but a different number of neutrons.

Ion: An ion is any electrically charged particle resulting from the loss or gain of electrons. Positive ions are called cations and negative ions are called anions.

Energy Sub-levels and Quantum Mechanics

Energy Sub-levels

With the exception of the first energy level, others are composed of several sub-levels closely clustered together. The sublevels are designated by the letters s, p, d, and f. Each supports a maximum level of electrons, and each sublevel has a limit to the number of electrons that it can hold.

Wave-Particle Duality

De Broglie stated that very small particles moving at high speed (such as electrons) have the ability to behave sometimes like material corpuscles and sometimes like wave phenomena.

Quantum Numbers

These indicate the location and properties of electrons. Each electron is characterized by four quantum numbers: the principal quantum number, the azimuthal (side) quantum number, the magnetic quantum number, and the spin quantum number.

Pauli Exclusion Principle

In a single atom, no two electrons can have all four quantum numbers equal; they must differ, at least in the value of one of their quantum numbers.