Physics Definition and Atom History CH1

Definition of Physics

• Physics deals with the fundamental properties and motion of matter.
• Matter is all physical substances around us that have mass and occupy space.
• The universe is composed of matter and energy.

History of the Atom (Greek Atom)

• Ancient Greek scientists believed matter was composed of four elements: earth, water, air, and fire.
• These elements combined in various proportions and were modified by wet, dry, hot, and cold essences.
• The concept of "atom" meaning indivisible, was used to describe the smallest part of these elements.
• Each type of atom was represented by a specific symbol.

Dalton's Atom

• In 1808, John Dalton proposed a model based on experiments.
• Elements are classified according to integral values of atomic mass.
• An element consists of identical atoms that react chemically in the same way.
• For example, all oxygen atoms are alike.

Thomson's Atom

• In the late 1890s, J.J. Thomson discovered electrons as an integral part of atoms.
• He visualized the atom as a "plum pudding" model, where electrons (plums) are embedded within a positively charged mass (pudding).
• The number of electrons balances the positive charge, making the atom electrically neutral.

Rutherford's Atom

• Rutherford's model suggested an atom is mostly empty space with electrons orbiting a small, dense, positively charged nucleus.

Bohr's Atom

• In 1913, Niels Bohr refined Rutherford's model.
• Bohr's model likened the atom to a miniature solar system, with electrons revolving in prescribed orbits or energy levels.
• For simplicity, Bohr's model, while not perfectly accurate, represents the structure effectively.
• This model was later refined by quantum chromodynamics (QCD)

The Atom (Structure)

• Atoms have two main components: a nucleus and orbiting electrons.
• The nucleus contains protons and neutrons (called nucleons).
• Neutrons have no electrical charge, while protons carry a positive charge.
• Electrons have a negative charge.
• Electrons are arranged in energy levels or shells.

Atomic Particles

• Protons: Larger and heavier than electrons, have a positive charge (+), and are located in the nucleus.
• Neutrons: Large and heavy, similar to protons but have no electrical charge, found in the nucleus.
• Electrons: Tiny and light, carry a negative charge (-), orbit the nucleus in shells.

Electron Binding Energy

• Energy required to remove an electron from an atom.
• Inner-shell electrons have higher binding energy than outer-shell electrons.
• Energetic particles can knock out inner-shell electrons only if their energy equals or exceeds the electron binding energy.

Shells

• Each atomic shell has a principal quantum number, starting with 1 for the K-shell, 2 for the L-shell and so forth.
• Electrons in a given shell can have a certain maximum capacity, based on the 2n^2 rule.
• The electron distribution is: 2, 8, 18, 32, 21, 9, and 2 in successive shells.

Electromagnetic Radiation

• Electrons transitioning between energy shells emit electromagnetic radiation.
• This radiation is quantized (exists in discrete energy packets called photons).
• Electromagnetic radiation is a transverse wave, where the electric and magnetic fields vibrate perpendicular to the direction of the wave motion.

Atomic Properties

• Atoms are electrically neutral in normal state (number of electrons = number of protons).
• The atomic number corresponds to the number of protons.
• Isotopes have the same number of protons but different numbers of neutrons.
• The mass number is the sum of protons plus neutrons.

Summary of Atomic Structure

• Atoms have a dense, positively charged nucleus where most of the mass is concentrated.
• The atom is essentially empty space, occupied mostly by electrons orbiting the nucleus.
• Shells determine probable electron locations based on quantized energy levels.

Additional notes

• Diagrams and figures are important visual aids for understanding the concepts.
• Practice calculations related to atomic numbers, mass numbers, isotopes etc.

Explore the foundational concepts of physics, including the properties and motion of matter. Delve into the historical development of atomic theory from Ancient Greece to Dalton and Thomson's models. This quiz covers significant milestones in our understanding of the atomic structure.