Chemistry

pH: measure of acidity and alkalinity pH pH quantifies how acidic or basic an aqueous solution is, defined by hydrogen ion activity. This article explains the scale, formulas, measurement methods, examples, history and pr…

Pharmaceutical chemistry (medicinal chemistry): an overview Pharmaceutical chemistry Pharmaceutical chemistry (medicinal chemistry) studies the chemical design, synthesis and properties of drugs, linking chemistry and pharmacology to discover and optimize therapeut…

Phase change (changes of state of matter) Phase change Transformation of matter between solid, liquid and gas driven by energy, temperature or pressure; includes melting, freezing, vaporization, condensation, sublimation and practical…

Phenol: properties, structure, production, uses and safety Phenol Phenol (C6H5OH) is an aromatic organic compound used as a chemical intermediate and historical antiseptic. This article summarizes its structure, production, main applications and…

Phlogiston theory: the historical chemical hypothesis of combustion Phlogiston theory Phlogiston theory was a pre‑modern chemical idea that combustion released a fire‑like substance called phlogiston. It shaped 17th–18th century chemistry until experiments and the o…

Phosgene (carbonyl chloride): properties, history and industrial uses Phosgene Phosgene (COCl2) is a colorless, toxic gas used industrially as a chemical building block. Noted for its haylike odor and delayed pulmonary injury, it was a major chemical weapon i…

Phosgene oxime (CX) Phosgene oxime Phosgene oxime (CX) is a synthetic nettle (urticating) chemical agent that causes rapid, severe skin and mucous membrane injury. It has no widespread civilian uses; exposure is pri…

Phosphate: chemistry, biological role, types, and uses Phosphate Phosphate (PO4^3−) is an oxyanion and the basis of many salts and esters; essential in biology and widely used in industry and agriculture. Covers structure, major forms, uses, and…

Phosphide — chemistry, structure, reactions and applications Phosphide Phosphide describes compounds containing phosphorus in a low (often −3) oxidation state, from the discrete P3− ion to covalent/metallic phosphides. Covers bonding, reactions (phosp…

Phosphine (PH3) — properties, production, uses, and safety Phosphine Phosphine (PH3), also called phosphane, is a colorless, flammable, and toxic phosphorus hydride gas. Overview of its properties, production, applications, and safety precautions.

Phosphite — inorganic anions and related compounds Phosphite Phosphite refers to the anions and salts derived from phosphorous acid (commonly the HPO3^2− ion). It contains phosphorus in the +3 oxidation state and appears in chemical, agricul…

Phosphonium: the phosphorus-centered cation and its derivatives Phosphonium Phosphonium refers to phosphorus-centered cations such as PH4+ and tetraorganophosphonium salts (R4P+). It is analogous to ammonium and important in organophosphorus chemistry, syn…

Phosphor (luminescent materials) Phosphor Materials that absorb energy and re-emit it as visible light. Phosphors are used in lamps, displays, LEDs, scintillators and glow-in-the-dark products and should not be confused wi…

Phosphoric acid (orthophosphoric acid) — properties, production, and uses Phosphoric acid An overview of phosphoric (orthophosphoric) acid: chemical identity, structure, common production methods, major industrial and food uses, safety considerations, and related compou…

Phosphorous acid (H3PO3): properties, structure, and uses Phosphorous acid Phosphorous acid, H3PO3, is a phosphorus(III) oxyacid used in synthesis and agriculture. This article summarizes its structure, chemical behavior, preparation, applications, and sa…

Phosphorus: element P, properties, allotropes, uses and impact Phosphorus Overview of phosphorus (P, atomic number 15, atomic weight ~30.97): its forms, chemistry, biological role, industrial uses, history, production and safety/environmental concerns.

Phosphorus pentafluoride (PF5) Phosphorus pentafluoride PF5 is a colorless, volatile phosphorus halide with a trigonal bipyramidal structure. It is a Lewis acid used in inorganic synthesis and notable for its dynamic (fluxional) bonding…

Phosphorus trichloride (PCl3): properties, production, uses, and safety Phosphorus trichloride Phosphorus trichloride (PCl3) is a colorless, reactive phosphorus halide used as an industrial intermediate for organophosphorus chemicals, produced by chlorinating elemental phosp…

Phosphorus(III) iodide (phosphorus triiodide) Phosphorus(III) iodide Phosphorus(III) iodide (PI3) is a covalent phosphorus halide used as an iodinating reagent in organic synthesis; it is reactive toward water and normally handled or generated under…

Phosphorus(III) oxide (phosphorus trioxide) Phosphorus(III) oxide An overview of phosphorus(III) oxide (P4O6, empirical P2O3): its structure, preparation, chemical behavior, uses, and safety considerations.

Phosphorus(V) chloride (phosphorus pentachloride) Phosphorus(V) chloride Phosphorus(V) chloride (PCl5) is a chlorinating reagent and inorganic phosphorus compound. It shows molecular and ionic structures, hydrolyzes vigorously, and is used in organic an…

Phosphorus(V) oxide (phosphorus pentoxide) Phosphorus(V) oxide Phosphorus(V) oxide (P4O10), commonly called phosphorus pentoxide, is a white hygroscopic solid used mainly as a powerful dehydrating agent and intermediate in phosphorus chemistry…

Photochemistry: the science of light-driven chemical change Photochemistry Photochemistry examines chemical reactions initiated or altered by light, covering principles, mechanisms, history, biological and atmospheric roles, and practical applications in…

Photodissociation (photolysis): how light breaks chemical bonds Photodissociation Photodissociation (photolysis) is the process by which photons break chemical bonds in molecules. This article explains mechanisms, wavelengths, examples, atmospheric roles, and pr…

Physical change — alterations in form or state of matter Physical change A physical change alters a substance's form, shape, or state without creating a new substance; examples include melting, freezing, dissolving, crystallization and mechanical deform…

Physical chemistry: fundamentals, methods, history, and applications Physical chemistry Physical chemistry applies physical principles to chemical systems, explaining energy, matter, and dynamics across scales with thermodynamics, kinetics, quantum theory and statisti…

Pi bond (π bond) Pi bond A pi (π) bond is a covalent bond formed by side-by-side overlap of p orbitals; typical in double and triple bonds, it restricts rotation and enables conjugation, aromaticity and ch…

Pigment: natural and synthetic substances that provide color Pigment Overview of pigments: particulate colorants used in art and industry, natural and synthetic sources, their properties and production, historical development, applications, and safe…

Pipette: laboratory instruments for measuring and transferring liquids Pipette A pipette is a laboratory tool for accurately measuring and transferring defined liquid volumes. Types range from simple droppers to precision adjustable micropipettes used in rese…

Platinum (chemical element and metal) Platinum Platinum is a dense, silvery-white precious metal (Pt, atomic number 78) valued for its chemical stability, catalytic activity and use in jewelry, industry and automotive emissions…

Plutonium Plutonium is a dense, radioactive actinide metal (symbol Pu, atomic number 94) with several isotopes used in nuclear fuel, weapons, and radioisotope power sources; it is chemically…

Pnictogen (Group 15) — nitrogen, phosphorus, arsenic, antimony, bismuth, moscovium Pnictogen Pnictogens (Group 15) are elements with five valence electrons, from gaseous nitrogen to heavy bismuth and synthetic moscovium. They display diverse chemistry, important compounds,…

Poison gas: properties, types, history, industrial uses, and safety Poison gas Overview of toxic gases: definitions, main categories and mechanisms, historical use as weapons, industrial roles, health effects, and safety measures for prevention and response.

Polar bond A polar bond is a covalent bond in which electrons are shared unequally, producing partial charges and an electrical dipole that affects molecular shape, interactions and propertie…

Polonium (element Po) Polonium Polonium (Po, atomic number 84) is a rare, highly radioactive metalloid discovered by Marie and Pierre Curie; it has few commercial uses and is notable for its toxicity and special…

Polybutadiene: properties, production, and major uses Polybutadiene Polybutadiene is a synthetic rubber made from 1,3-butadiene. Known for wear resistance and elasticity, it is used chiefly in tires and as an impact modifier for plastics and in spe…

Polycarbonate: properties, uses, history and safety considerations Polycarbonate Polycarbonate is a strong, lightweight transparent thermoplastic used for lenses, electronics housings, glazing and discs; this article covers its properties, production, applicati…

Polychlorinated Biphenyls (PCBs): chemistry, uses, risks and regulation Polychlorinated biphenyl Polychlorinated biphenyls (PCBs) are persistent, chlorinated industrial chemicals once used in electrical equipment and fluids. They bioaccumulate, pose health risks, and are now t…

Polyene: conjugated unsaturated hydrocarbons — structure, properties and uses Polyene Polyene molecules contain chains of alternating single and double carbon–carbon bonds. This article explains their structure, electronic effects, natural examples, reactivity, synt…

Polymer: definition, structure, history and applications Polymer An accessible overview of polymers: what they are, how they form, major natural and synthetic types, production methods, common uses, and key distinctions including environmental a…

Polymer chemistry: principles, classes, properties and applications Polymer chemistry Overview of polymer chemistry: macromolecules, synthesis and structure, major natural and synthetic classes, characterization, thermal and solution behavior, and modern challenges…

Polymerization — formation, mechanisms, and applications of polymers Polymerization Polymerization is the chemical process by which small molecules (monomers) link to form large chain-like or network macromolecules (polymers). Covers mechanisms, types, properties,…

Polymorphism (materials science): crystal forms, types, and significance Polymorphism (materials science) Polymorphism is the ability of a crystalline solid to adopt two or more crystal structures. This article explains types, mechanisms, characterization methods, practical consequence…

Polystyrene Polystyrene is an aromatic polymer made from the monomer styrene. It is a widely used thermoplastic found in solid and foamed forms for packaging, insulation, consumer goods and mo…

Polytetrafluoroethylene (PTFE): properties, history, and uses Polytetrafluoroethylene Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer noted for chemical inertness, low friction and water/oil repellence. Developed in the 20th century, it is used from cook…

Polyurethane: chemistry, types, uses, and important distinctions Polyurethane Comprehensive overview of polyurethane (PU/PUR): its chemistry and manufacture, material varieties and properties, principal uses, brief history, and safety and recycling considera…

Polyvinyl chloride (PVC): properties, production, uses and concerns Polyvinyl chloride Polyvinyl chloride (PVC) is a versatile thermoplastic made by polymerizing vinyl chloride. This article covers its chemistry, types, manufacturing, common applications, and environ…

Post-transition metals Post-transition metal Post-transition metals (poor metals) are p-block elements to the right of the transition metals; they are generally softer, often more electronegative, have lower melting points, a…