Understanding Electrostatics: Principles, Models, and Applications

Posted on Mar 19, 2025 in Chemistry

Electrostatics: An Introduction

Electrostatics is the study of electric charges at rest. This field explores the phenomena associated with stationary electric charges and their interactions.

Early Discoveries

The history of electrostatics dates back to ancient times:

  • Thales of Miletus: Observed that rubbing amber with cat fur attracted feathers.
  • William Gilbert: Manufactured the versorium, a device to detect electric charge.
  • Charles du Fay: Noted that rubbing glass with silk electrified objects, leading to attraction and repulsion. He deduced two types of electricity: resinous and vitreous.
  • Benjamin Franklin: In 1747, named the charge acquired by rubbed bodies as positive and the charge lost as negative.

Key principle: Bodies with the same charge sign repel each other, while those with opposite signs attract.

Electroscope

Invented by Nollet, the electroscope detects charged bodies and electrifies them through contact or induction.

  • If a charged bar touches the electroscope, the plates acquire the same charge.
  • If the electroscope is charged by induction, the plates have opposite charges to the inducing object.

Electric Pendulum

In 1780, Coulomb used an electric pendulum, consisting of an insulating ball hanging by a thread, to study electrostatic forces.

  • If a charged rod touches the ball, the ball becomes charged.
  • If a rod with the opposite charge is brought near, the ball is attracted.
  • If a rod with the same charge is brought near, the ball is repelled.
  • Discharge the ball by touching it with your fingers.

Gilbert’s Versorium

Around 1600, Gilbert’s versorium featured a metal needle that swiveled when brought near a charged object.

Atomic Structure and Charge

Electrons in atoms carry a negative charge.

  • Robert Millikan (1909): Measured the mass and charge of the electron.
  • Protons: Particles with the same charge magnitude as electrons but positive. Their mass is approximately 1840 times that of an electron.

Atomic Models

  • Thomson’s Model: Proposed that the atom is a positively charged mass with electrons embedded within it to maintain neutrality.
  • Rutherford’s Model: Suggested that the atom consists of a small, dense, positively charged nucleus surrounded by orbiting electrons.
  • Bohr’s Model: Refined the model by stating that electrons orbit the nucleus in specific energy levels or orbits.
  • Modern Model: Atoms have a nucleus and an orbital region where electrons are located.

Atomic Number and Mass Number

  • Atomic Number (Z): Indicates the number of protons.
  • Mass Number (A): Indicates the total number of protons and neutrons.
  • In a neutral atom: Number of Electrons = Number of Protons = Z
  • Number of Neutrons = A – Z

Isotopes

Isotopes are atoms with the same atomic number (Z) but different mass numbers (A).

Atomic Mass

The average atomic mass of an element is calculated as:

Maverage = (Mass of Isotope 1 × % Abundance 1 + Mass of Isotope 2 × % Abundance 2) / 100 (in atomic mass units, u)

Ions

  • Cation: An atom that loses electrons becomes a positive ion (cation).
  • Anion: An atom that gains electrons becomes a negative ion (anion).

Radioactivity

Radioactivity involves:

  1. The loss or gain of particles.
  2. The rupture of the nucleus to form smaller nuclei (nuclear fission).
  3. The union of small nuclei to form a larger nucleus (nuclear fusion).

Types of Radiation

  • Alpha Particles: Composed of 2 protons and 2 neutrons, carry a positive charge, and have low penetrating power.
  • Beta Particles: Consist of electrons, carry a negative charge, and have moderate penetrating power.
  • Gamma Rays: Neutral radiation with high penetrating power.

Nuclear Fission

The nuclei of radioactive isotopes, such as uranium, break apart to form smaller nuclei.

Nuclear Fusion

Very small atomic nuclei combine to form larger ones.

Applications of Radioactivity

  1. Power Generation: Used in nuclear power plants and batteries.
  2. Research and Experiments: Determines the age of archaeological findings, chemical tracers, and forensic investigations.
  3. Medicine: Diagnoses diseases and treats certain cancers.

Radioactive Waste

  • Dangerous
  • Extremely durable
  • Low to medium level waste ceases to be dangerous to humans after 300 years.
  • High-level waste can remain harmful for thousands of years.