Atoms, composed of protons, neutrons, and electrons, form elements. The periodic table organizes elements by valence electrons and electron shells, dictating their chemical behavior. Metals, non-metals, and semimetals are categorized.

Atoms bond to form molecules and compounds. Covalent bonds involve electron sharing, influenced by electronegativity. Ionic bonds result from electron transfer, creating ions. Metallic bonds feature delocalized electrons in metals. Polarity in covalent bonds creates dipoles and intermolecular forces.

Matter exists as solids, liquids, and gases, defined by particle arrangement and energy. Temperature is the average kinetic energy, and entropy is disorder. Phase changes and plasma are also discussed.

Matter is categorized into pure substances and mixtures. Mixtures can be homogeneous or heterogeneous, including solutions, suspensions, and colloids. Chemical reactions involve synthesis, decomposition, and replacement, guided by stoichiometry and conservation of mass.

Acids donate protons, and bases accept them, forming conjugate pairs. pH measures acidity based on hydronium ion concentration. Redox reactions involve changes in oxidation numbers and electron transfer, with oxidation and reduction happening simultaneously.

Electrons are described by four quantum numbers (n, l, ml, ms) defining shells, subshells, orbitals, and spin. The Aufbau principle dictates electron configuration, determining valence electrons.