Atomic Theory and Models Quiz

Atomic Theory

• Democritus hypothesized that matter could be divided into smaller and smaller pieces until a point where it could no longer be divided. He called this indivisible piece an atom.
• John Dalton proposed that all matter is composed of atoms.
• Atoms of the same element are identical in size, mass, and chemical properties.
• Atoms of different elements are different.
• Atoms cannot be subdivided, created or destroyed.
• Atoms combine in whole number ratios to form compounds.

J.J. Thomson

• Discovered negatively charged particles (electrons)
• Proposed the plum pudding model, describing atoms as a sphere of positive charge with negatively charged electrons embedded within it.

Ernest Rutherford

• Conducted the gold foil experiment.
• Discovered a dense, positively charged nucleus at the center of the atom.
• Proposed the nuclear model of the atom, with electrons orbiting the nucleus.
• Suggested the existence of the neutron, a neutral particle in the nucleus that contributes to the mass of the atom.

Rutherford's Experimental Design

• Alpha particles (positively charged) are directed at a thin gold foil.
• Most alpha particles passed straight through, suggesting that atoms are mostly empty space.
• Some alpha particles were deflected, indicating a dense, positively charged nucleus. Alpha particles were deflected by a positive nucleus.

Max Planck

• Observed that excited gases under low pressure emit light at specific wavelengths (line spectra), indicating that energy is emitted in discrete quantities.
• Introduced the concept of quanta, the smallest packet of energy that can be absorbed or emitted.

Niels Bohr

• Proposed the planetary model of the atom, with electrons orbiting the nucleus in specific, allowed energy levels.
• Electrons can only exist in specific energy levels (quantized energy).

Albert Einstein

• Explained the photoelectric effect, suggesting that light behaves as a stream of particles (photons).
• Each photon has a specific energy, and if this energy is high enough, it can cause an electron to jump to a higher energy level.

Louis de Broglie

• Proposed that electrons, like light, possess both wave-like and particle-like properties (wave-particle duality).

Erwin Schrödinger

• Developed a model where electrons are described by probability distributions (orbitals) rather than precise paths.
• Electrons are found in regions of space called orbitals, where the probability of finding them is highest.
• The concept of precisely determining an electron's location and momentum is impossible (Uncertainty Principle). The position or momentum of an electron cannot be precisely determined simultaneously (Uncertainty Principle).

Homework Assignment

• Read pages 143-146.
• Answer questions 1-3, 10 on page 147.
• Read pages 148-151.
• Answer questions 1, 3 on page 152.