Understanding Electrostatics: Principles and Applications

Posted on Mar 5, 2025 in Chemistry

Electrostatics

Early Observations

Thales observed that rubbing amber with cat fur attracted feathers. Gilbert manufactured the versorium.

Types of Electricity

Charles du Fay discovered that rubbing glass with silk electrified objects, and similar objects repelled each other. He deduced two types of electricity: resinous and vitreous.

In 1747, Franklin named the charge gained by rubbed bodies as positive and the charge lost as negative. Bodies with the same charge repel, while those with different charges attract.

Electroscope

The electroscope, invented by Nollet, detects charged bodies and electrifies them by contact or induction.

  • If a charged bar touches the electroscope, the plates acquire the same charge.
  • If the electroscope is charged by induction, a positive charge induces a negative charge on the sheet.

Electric Pendulum

In 1780, Coulomb created an electric pendulum consisting of an insulating ball hanging by a thread.

  • 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.
  • The charge can be discharged by touching the ball with your fingers.

Versorium

Gilbert’s versorium (1600) uses a metal needle that swivels when a charged body is brought near.

Atomic Structure

Electrons in atoms have a negative charge. In 1909, Millikan measured the mass and charge of the electron.

A proton has the same charge as an electron but is positive, and its mass is 1840 times that of the electron.

Atomic Models

Thomson’s Model

Thomson proposed that the atom is a mass of positive charge with electrons embedded within it, resulting in a neutral atom.

Rutherford’s Model

Rutherford proposed that the atom consists of a small nucleus containing positive charge and mass, with electrons revolving around it.

Bohr’s Model

Bohr suggested that electrons orbit the nucleus in specific orbits.

Current Model

The current model states that atoms have a nucleus and an orbital region where electrons are located.

Atomic Number and Mass Number

The atomic number (Z) indicates the number of protons.

The mass number (A) indicates the total number of protons and neutrons.

  • Number of Electrons = Number of Protons = Z
  • Number of Neutrons = A – Z

Isotopes

Isotopes are atoms with the same Z but different A.

Atomic Mass

The average atomic mass is calculated as: (mass of isotope 1 x % abundance 1 + mass of isotope 2 x % abundance 2) / 100 (in atomic mass units, u).

Ions

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

Radioactivity

  1. Radioactivity involves the loss or gain of particles.
  2. Nuclear fission is the splitting of a nucleus into smaller nuclei.
  3. Nuclear fusion is the joining of small nuclei to form a larger nucleus.

Types of Radiation

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

Nuclear Fission

Nuclear fission involves the splitting of large, radioactive isotopes (e.g., uranium) into smaller atoms.

Nuclear Fusion

Nuclear fusion involves the joining of very small atomic nuclei to form larger ones.

Applications of Radioactivity

  1. Power Generation: Used in nuclear power plants and batteries.
  2. Research and Experiments: Used to determine the age of archaeological findings, as chemical tracers, and in forensic investigations.
  3. Medicine: Used to diagnose diseases and treat some cancers.

Radioactive Waste

  • Dangerous
  • Extremely durable
  • Low to medium level waste ceases to be dangerous to humans after 300 years.
  • High level waste can take thousands of years to become harmless.