AP Chem unit 4: Atomic Structure

Democritus

First to theorize that all matter was composed of indivisible particles called "atomos."

Aristotle

Disagreed with Democritus, arguing matter was continuous; his views dominated science for centuries.

Joseph Priestley

Prepared pure oxygen; discovered carbon dioxide and nitrous oxide; called oxygen "dephlogisticated air."

Antoine Lavoisier

Disproved phlogiston theory; proved combustion involves oxygen; formulated the Law of Conservation of Mass.

Joseph Proust

Formulated the Law of Definite Composition (compounds always have the same proportion of elements).

John Dalton

Proposed the Atomic Theory of Matter; Law of Multiple Proportions.

J.J. Thomson

Discovered the electron using the cathode ray tube; determined the electron's charge-to-mass ratio; proposed the "plum pudding" model.

William Crookes

Developed the Cathode Ray Tube (Crookes' Tube).

Robert Millikan

Determined the exact charge and mass of an electron using the Oil-Drop Experiment.

Eugen Goldstein

Discovered the proton using a modified cathode ray tube.

Henri Becquerel

Discovered radioactivity by observing uranium's effect on photographic plates.

William Roentgen

Discovered X-rays.

Ernest Rutherford

Conducted the gold foil experiment; discovered the nucleus; proposed the nuclear model of the atom; identified and named alpha, beta, and gamma radiation.

Ernest Marsden

Rutherford's graduate student who actually conducted the gold foil experiment.

Neils Bohr

Proposed the planetary model of the atom; explained atomic line spectra; suggested electrons exist in specific energy levels.

Johann Balmer

Developed an equation to calculate the wavelengths of visible light emitted by hydrogen.

Johannes Rydberg

His constant (R_H) is used in equations to calculate the energy of electrons in hydrogen.

Max Planck

Proposed Quantum Theory; energy is emitted or absorbed in discrete packets called "quanta."

Albert Einstein

Explained the Photoelectric Effect; proposed that light consists of particles called "photons"; E = hν.

Louis de Broglie

Proposed that all matter has wave-like properties (wave-particle duality).

James Chadwick

Discovered the neutron.

Law of Conservation of Mass

Matter cannot be created or destroyed in a chemical reaction.

Law of Definite Composition

A compound always contains the same elements in the same proportions by mass.

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

Dalton's Atomic Theory

1) Elements made of atoms. 2) Atoms of same element identical. 3) Atoms of different elements differ. 4) Compounds form in whole-number ratios. 5) Atoms are rearranged in reactions.

Plum Pudding Model

J.J. Thomson's model; atom is a sphere of positive charge with electrons embedded within it.

Nuclear Model

Rutherford's model; atom has a tiny, dense, positive nucleus surrounded by electrons.

Planetary Model

Bohr's model; electrons orbit the nucleus in specific, fixed energy levels.

Alpha Particle (α)

Helium nucleus (2 protons, 2 neutrons); charge +2; low penetrating power.

Beta Particle (β)

High-speed electron; charge -1; moderate penetrating power.

Gamma Radiation (γ)

High-energy electromagnetic radiation; no charge; high penetrating power.

Strong Nuclear Force

The force that holds protons and neutrons together in the nucleus ("neutron glue").

Radioactivity

The process by which unstable atoms (with atomic number > 82) emit radiation to become more stable.

Cathode Rays

Streams of electrons originating from the cathode in a cathode ray tube.

Photoelectric Effect

Phenomenon where electrons are ejected from a metal surface when light of a sufficient frequency shines on it.

Photon

A particle of light; a quantum of electromagnetic energy.

Quantum Theory

Energy is absorbed and emitted in discrete amounts (quanta), not continuously.

Line Spectrum

The unique set of discrete wavelengths of light emitted by an excited element.

Continuous Spectrum

The uninterrupted band of all wavelengths of light.

Energy Level (n)

A specific, quantized energy state that an electron can occupy in an atom.

Ground State

The lowest energy state of an electron in an atom.

Excited State

A higher energy state of an electron in an atom.

Electromagnetic Radiation

A form of energy that exhibits wave-like behavior; includes radio, microwave, IR, visible, UV, X-ray, and gamma rays.

Wavelength (λ)

The distance between two consecutive peaks on a wave.

Frequency (ν)

The number of waves that pass a point per second (units: Hz or s⁻¹).

Speed of Light (c)

3.00 x 10^8 m/s; constant for all electromagnetic radiation in a vacuum.

c = λν

The wave equation; relates the speed of light to its wavelength and frequency.

E = hν

The energy of a photon; h is Planck's constant (6.624 x 10^-34 J·s).

λ = h / (m*v)

The de Broglie equation; calculates the wavelength of any particle with mass.

E = R_H * (1/n²)

Calculates the energy of an electron at a specific energy level (n) in a hydrogen atom.

Rydberg Constant (R_H)

2.180 x 10^-18 J

Elight = RH * (1/nf² - 1/ni²)

Calculates the energy of a photon emitted when an electron falls from a higher (ni) to a lower (nf) energy level in hydrogen.

Maximum Electrons in an Energy Level

2n² (where n is the energy level number)