Atomic Structure Fundamentals: Models, Particles, and Radioactivity

Atomic Structure: Models and Definitions

The Plum Pudding Model

The Plum Pudding Model considers the atom as a ball of positive charge with electrons (negative charge) embedded.

The Rutherford Model

Rutherford's Bombardment Experiment

Rutherford tested the Rutherford Model by bombarding metal foil atoms with alpha particles (projectiles harder than atoms).

Experimental Results

• Result 1: The majority of alpha particles passed through the foil undeflected.
• Result 2: Some of these particles suffered deviation.
• Result 3: Very few rebounded and turned back.

Interpretation and Consequences

The interpretation was that particles that crossed the foil showed that atoms are not solid, but contain much empty space.

The Consequences of the Rutherford Atomic Model are that the atom is composed of:

• A small nucleus with protons and neutrons, which concentrates virtually all the mass and has a small positive electric charge.
• A surrounding area (the electron shell or bark) in which electrons are in constant motion.

Fundamental Atomic Definitions

• The Atomic Number (Z): The number of protons in an atom, typical of each chemical element. The number of electrons is the same as that of protons in a neutral atom.
• The Mass Number (A): The sum of protons and neutrons in an atom.
• Ion: An atom with a missing or excess number of electrons. If an atom loses an electron, it becomes a positive ion or cation.
• The Electron Shell (Bark): Consists of all the electrons rotating around the atom, carrying a negative electric charge.

Atomic Components and Mass Calculation

A More Complex Atomic Model

An atom consists of electrons, protons, and neutrons. Protons and neutrons are in the nucleus, and electrons are in the shell.

Atomic Particles

• Protons: Particles that account for almost all the mass of the atom. They carry the same magnitude of charge as the electron, but positive, and are located in the core (nucleus).
• Neutrons: Particles with the same mass as the proton but without electric charge.

Mass Calculations

• The Atomic Mass Unit (AMU): Calculated relative to the carbon atom, used to determine the relative atomic masses of other elements.
• Molecular Mass: Calculated by adding the masses of the component atoms in a molecule.

Isotopes and Radioactivity

Isotopes and Alpha Particles

• Isotopes: Atoms of the same element that have the same atomic number (Z) but different mass numbers (A). They have the same number of protons but different numbers of neutrons.
• Alpha (α) Particles: Smaller than atoms, but very heavy, with a mass four times greater than the hydrogen atom and a double positive charge (twice the magnitude of an electron charge).

Radioactive Isotopes (Radioisotopes)

Radioactive elements have useful applications, including constituting a major source of electric power and serving as allies in medicine to cure certain illnesses of our body.

Why Are Some Isotopes Radioactive?

In the nuclei of radioactive isotopes (radioisotopes), changes (nuclear reactions) occur that consist of the expulsion of some particles from the nucleus.

Nuclear Radiation Safety and Types

Are Nuclear Radiations Dangerous? All nuclear radiations are dangerous and can break molecules.

Types of Radiation:

1. Radiation α (Alpha)
2. Radiation β (Beta)
3. Radiation γ (Gamma): This is the most dangerous type.

Utilization of Radioactivity in Medicine

• As Tracers: An injected dose of radioactive elements can be photographed to track processes within the body.
• Radiotherapy: Gamma radiation is used to kill cancerous cells.