Atomic Theory & Quantum Mechanics

Atomic Theory Evolution

• Aristotle (350 BC) believed all matter was composed of four elements: air, water, earth, and fire and that matter was continuous.
• Democritus (400 BC) suggested the concept of atoms as indivisible particles, but lacked experimental backing.
• Dalton's Atomic Theory (early 1800s) stated matter consists of indivisible atoms.
• Atoms of a given element are identical, while atoms of different elements vary.
• Atoms combine in simple, whole-number ratios to form compounds.
• Dalton's model portrayed atoms as featureless solid spheres and explained the Law of Conservation of Mass, Definite Composition, and Multiple Proportions.
• Dalton's model did not include isotopes or subatomic particles.
• J.J. Thomson (1897) discovered the electron (e⁻) using the cathode ray tube (CRT).
• Thomson proposed the plum pudding model, with electrons within a positive sphere.
• Ernest Rutherford (1911) discovered the nucleus through the gold foil experiment.
• The nucleus is a small, dense, positively charged center, with the atom mostly empty space.
• Rutherford proposed the nuclear model, where electrons orbit the nucleus.
• Eugene Goldstein identified protons (p⁺) using a modified CRT.
• James Chadwick (1932) discovered the neutron (n), explaining mass discrepancies in atoms.
• Bohr's model: Electrons orbit the nucleus in specific energy levels.

Subatomic Particles

• Protons: Located in the nucleus, have a +1 charge, and a mass of approximately 1 u.
• Electrons: Located in orbitals, have a -1 charge, and a mass of approximately 1/2000 u.
• Neutrons: Located in the nucleus, have a 0 charge, and a mass of approximately 1 u.

Introduction to Chemistry

• Chemistry is the study of matter, its properties, and reactions.
• Matter has mass and volume.
• Light, heat, and sound are forms of energy, not matter.
• Matter's ability to absorb or emit energy is crucial.
• Energy travels as waves.
• The electromagnetic spectrum categorizes radiation types by wavelength or frequency.
• Visible light interacts the most with matter and enables human vision.
• The highest point on a wave is the crest.
• The maximum displacement of a wave, indicating intensity, is the Amplitude.
• A node is the point of zero displacement in a wave.
• The lowest point on a wave is the trough.
• Wavelength: The distance between two successive points on a wave.
• Frequency: The number of waves or cycles that occur in a given time frame, measured in Hertz.
• Wave equations include formulas such as v=fx and c=fx, where c is the speed of light (approximately 3.00x10^{8} m/s).
• Blackbody radiation is when heated solids emit energy in a pattern: dull red to blinding white.

UV Catastrophe

• Scientists observed amplitude dropped to zero in the UV spectrum, contrary to expectations.
• The UV catastrophe was the first evidence of light not acting like a wave.

Wave-Particle Duality

• Max Planck proposed light is emitted in discrete "bursts" called quanta, explaining the UV Catastrophe, and supported the wave-particle duality theory.
• The photoelectric effect: Light on metal can create an electric current if it has enough energy, depends on the color of light, not just intensity.
• Einstein explained light as photons that collide with atoms, causing movement.
• Light demonstrates both wave and particle characteristics.
• Light's observed nature differs based on the experiment.
• Niels Bohr used spectroscopy to address issues in Rutherford's model.
• Flame tests in the early 1900s showed elements produce unique flame colors.

Emission Spectrum

• An emission spectrum is created when light from an element is split, showing distinct color lines.
• Electrons orbit the nucleus at specific distances called stationary states or energy levels.
• Electrons exist only at certain energy levels, with 7 confirmed levels.
• Electrons absorb energy to move to a higher energy level (excited state).
• When electrons return to the ground state from the excited stated, they emit energy as light.
• Each element has a unique spectrum due to the number of protons.
• More protons result in a stronger attraction to electrons, altering energy level distances and energy required for transitions.
• Spectra confirm elements present.
• The maximum number of electrons in an energy level is given by the formula: 2n^2.
• In hydrogen, transitions from higher energy levels to n=2 produce 4 lines and is called the Balmer Series.
• Transitions from higher energy levels to n=1 create 5 lines in the UV Range and is called the Lyman Series.
• Transitions from higher energy levels to n=3 produce 3 lines in the Infrared Range and is called the Paschen Series.
• The Balmer-Rydberg Equation relates to spectral lines
• The Rydberg constant is $1.097 \times 10^7 $

Explore the relationship between wavelength and frequency of electromagnetic radiation, the UV catastrophe, Max Planck's explanation of blackbody radiation, and the photoelectric effect. Also includes Bohr's model of the atom, emission spectrum, and electron transitions.