Features of the Atom and Coulomb's Law

Features of the Atom

• Atoms have two types of electrical charges.
• Like charges repel each other, opposite charges attract.
• Coulomb's Law describes the force between charges. The force is directly proportional to the product of their magnitudes and inversely proportional to the square of the separation distance.

Coulomb's Law

• Formulated by Charles Coulomb.
• The coulomb (C) is the unit of electrical charge, named in his honor.

Other Electrical Discoveries

• Luigi Galvani explored electricity from chemical changes.
• Count Alessandro Volta invented the wet battery, leading to studies of electrolysis.
• Electrolysis involves passing an electric current through an electrolyte, causing chemical reactions.
• Electrolytes are substances that produce an electrically conductive solution in a polar solvent like water.
• Sir Humphry Davy and Michael Faraday studied the electrical decomposition of compounds.
• Faraday's law quantifies electrolytic effects.
• George Stoney proposed the name "electrine" for the unit electrical charge.

The Electron

• William Crookes discovered cathode rays, a stream of particles from the negative electrode in a vacuum tube.
• Cathode rays are negatively charged particles.
• Julius Plucker, Johann Hittorf, and others showed cathode rays have the following properties:
  • Emitted from the cathode in an evacuated tube.
  • Travel in straight lines.
  • Cast shadows.
  • Cause fluorescence in materials they strike.
  • Are attracted to positively charged objects.
• Sir Joseph John Thomson determined the velocity and the ratio of electric charge (e) to mass (m) for cathode rays.
• Cathode rays are now called electrons, which are negatively charged particles found in all atoms.
• Thomson's discovery revolutionized atomic structure understanding.

The Electron (Cont.)

• Eugene Goldstein discovered canal rays, positively charged particles that pass through holes in the cathode.
• Canal rays are now known as protons, which have a positive charge.

Thomson's Plum Pudding Model

• Proposed by J.J. Thomson in 1904.
• Electrons are embedded within a positively charged "pudding" or "muffin".

Natural Radioactivity

• Wilhelm Roentgen discovered X-rays in 1895, which challenged the idea of an indestructible atom.
• Antoine Becquerel and Marie Curie observed radioactivity in 1890s, where some atoms spontaneously break down and emit rays.
• Uranium materials emit Becquerel rays.
• Pierre and Marie Curie isolated polonium and radium, which are radioactive substances.
• Marie Curie won a second Nobel Prize for this work.

Natural Radioactivity (Cont.)

• Ernest Rutherford unraveled the nature of Becquerel rays, identifying alpha, beta, and gamma rays.
• Alpha rays are positively charged particles.
• Beta rays are negatively charged particles.
• Gamma rays are uncharged particles (high-energy electromagnetic radiation).

Nuclear Model

• Rutherford's experiment (gold foil experiment) showed that atoms are mostly empty space with a dense, positively charged nucleus.
• Alpha particles were directed at a thin gold foil and most passed through, some were deflected, and a few bounced back.
• Positively charged electrons are located outside the nucleus.

Rutherford's Nuclear Model (Cont.)

• Rutherford calculated the relative size of the nucleus and electron space.
• The nucleus is much smaller than the atom itself.

The Nucleus

• Rutherford's experiment led to the investigation of the nucleus.
• The number of positive charges in the nucleus increases progressively for each element consecutively.
• This means the nuclear charge is fundamental to an element's identity.

Atomic Number

• Atomic number (Z) is the number of protons in an atom's nucleus.
• In a neutral atom, the number of protons equals the number of electrons.
• Z = number of electrons

Neutron

• James Chadwick discovered the neutron in 1932.
• Neutrons have a mass similar to protons but no electrical charge.

Atomic Structure Summary

• Protons, neutrons, and electrons are fundamental particles that make up atoms.
• Mass number (A) is the sum of protons and neutrons.
• A = protons + neutrons (for neutral atoms).

Representing Atoms

• Chemical symbols often include a superscript (mass number) and a subscript (atomic number).
• Example: ¹²₆C (mass number 12, atomic number 6).

Isotopes

• Isotopes are atoms of the same element with different atomic masses.
• They have the same atomic number (Z) but different mass numbers (A).
• Example: Hydrogen isotopes (protium, deuterium, tritium).

This quiz covers key concepts related to the features of atoms, including electrical charges and Coulomb's Law. You'll also learn about important figures in the field of electricity and their contributions, such as Galvani and Volta. Test your understanding of electrolytes and the principles of electrolysis in this comprehensive quiz.