chem complete review

Democritus

Theorized that all matter is made of tiny, indivisible particles called atoms.

John Dalton

Proposed Dalton’s Atomic Theory — each element is made of identical atoms; atoms combine in fixed ratios to form compounds.

J.J. Thomson

Discovered the electron using the cathode-ray experiment; proposed the “plum pudding” model of the atom.

Ernest Rutherford

Conducted the gold-foil experiment and discovered the nucleus; showed that an atom is mostly empty space with a small, dense, positively charged center.

Niels Bohr

Proposed that electrons orbit the nucleus in specific energy levels and can jump between levels by absorbing or releasing energy.

James Chadwick

Discovered the neutron, a neutral particle with mass similar to that of a proton.

Erwin Schrödinger

Developed the quantum mechanical model; electrons move in regions of probability called orbitals (electron cloud model).

Dalton’s Postulates

All matter is composed of atoms; atoms of the same element are identical; atoms combine in whole-number ratios; chemical reactions rearrange atoms.

Rutherford’s Nuclear Model

Atom has a dense, positive nucleus; electrons move in empty space around it.

Bohr’s Model

Electrons orbit the nucleus in fixed energy levels (shells).

Modern Quantum Model

Electrons exist in orbitals within energy levels; position cannot be precisely known.

Electromagnetic Spectrum

The range of all types of electromagnetic radiation, from radio waves to gamma rays.

Energy–Frequency Relationship

E = hν — energy increases as frequency increases.

Wavelength–Frequency Relationship

c = λν — wavelength decreases as frequency increases.

Photon

A particle of light energy emitted when an electron moves to a lower energy level.

Atomic Emission Spectrum

The set of specific wavelengths emitted by electrons falling to lower energy levels; unique for each element.

Average Atomic Mass

Weighted average of all isotopes of an element

Protons

Positively charged particles in the nucleus; atomic number equals number of protons.

Neutrons

Neutral particles in the nucleus; mass number minus atomic number.

Electrons

Negatively charged particles surrounding the nucleus; equal to protons in a neutral atom.

Electron Configuration

Arrangement of electrons in energy levels, sublevels, and orbitals.

Energy Levels

Regions around the nucleus where electrons are likely found (n = 1, 2, 3…).

Sublevels

s, p, d, f — describe the shape of orbitals.

Valence Electrons

Electrons in the outermost energy level that determine chemical reactivity.

Orbital Diagram

Shows the distribution of electrons using arrows in boxes representing orbitals.

Kinetic Molecular Theory

Describes motion of particles — all matter is made of constantly moving particles; temperature measures average kinetic energy.

Change in Atomic Models Over Time

Atom models evolved from solid spheres → plum pudding → nuclear → planetary → quantum mechanical model.

Periods

Horizontal rows; indicate the number of energy levels.

Groups/Families

Vertical columns; elements have similar valence electron configurations and properties.

Atomic Number Trend

Increases left to right and top to bottom.

Valence Electron Trend

Increases across a period.

Metal vs. Nonmetal

Metals on the left (conductive, malleable); nonmetals on the right (brittle, poor conductors).