Understanding Atomic Theory: Dalton to Nuclear Fusion

Posted on Apr 1, 2025 in Chemistry

Understanding Atomic Theory

· Dalton’s Atomic Theory: Matter is composed of indivisible and indestructible particles called atoms. Each chemical element consists of identical atoms, distinct from those of other elements. Chemical compounds form through the union of atoms from different elements in fixed ratios.

· Chemical Element: A substance that cannot be broken down into simpler substances, consisting of only one type of atom (refer to the Periodic Table).

· Compound: A substance that can be broken down into simpler substances, composed of atoms from more than one element (e.g., Water, Sodium Chloride).

· Electrolysis and New Theories: Experiments suggested that atoms possess an internal structure with an electrical nature.

Subatomic Models

· Thomson’s Plum Pudding Model: Thomson discovered the electron, a subatomic particle with a negative charge. Key observations included:

  • Two types of electric charges exist: positive (+) and negative (-).
  • Opposite charges attract, while like charges repel.
  • Electric charge can be transferred between objects.
  • The strength of attraction or repulsion increases as the distance between charges decreases.

· Plum Pudding Model: Electrons, being small particles with negative charges, are distributed within a sphere of positive charge, resulting in an electrically neutral atom.

· Rutherford’s Model: Proposed the existence of protons and neutrons in addition to electrons. Protons carry a positive charge equal in magnitude to the electron’s negative charge and possess a significantly larger mass. Neutrons are electrically neutral and have a mass nearly identical to that of protons. Rutherford’s model suggested:

  • Atoms consist of protons, neutrons, and electrons.
  • The number of protons and electrons in an atom is equal, making the atom electrically neutral.
  • Protons and neutrons reside in a small, central nucleus, while electrons orbit this nucleus in a larger space called the electron cloud.

Atomic Structure

· Atomic Number (Z): The number of protons in an atom’s nucleus, defining the element (e.g., Carbon = 6).

· Mass Number (A): The total number of protons and neutrons in an atom’s nucleus (N = A – Z).

· Isotopes: Atoms with the same atomic number but different mass numbers.

Radioactivity

· Radioactivity: The phenomenon of unstable nuclei disintegrating.

Types of Radiation:

  • Alpha (α): Composed of helium nuclei (two protons and two neutrons).
  • Beta (β-): High-speed electrons.
  • Gamma (γ): Electromagnetic radiation similar to light or X-rays, but with higher energy.

Half-Life: Each radioisotope decays at a specific rate, characterized by its half-life – the time required for half of the initial nuclei to disintegrate. A shorter half-life indicates greater radioisotope instability.

Applications of Radioisotopes:

  • Diagnostic Imaging: Radiographs for medical diagnosis.
  • Cancer Treatment: High-energy radiation to destroy cancer cells.

Nuclear Reactions

· Nuclear Fission: The splitting of an atom’s nucleus when bombarded with neutrons, releasing energy and additional neutrons.

· Nuclear Fusion: The combination of small nuclei to form larger nuclei, releasing a significant amount of energy (e.g., hydrogen atoms fusing to form helium atoms).