Chemistry

Helium is a colorless, odorless, inert element with atomic number 2. It is the second-lightest and second-most abundant element in the universe.

Henri Kagan is a French chemist whose research established influential methods and principles in asymmetric catalysis and the use of samarium reagents in organic synthesis.

Henry Cavendish was a British experimental scientist known for characterizing hydrogen, investigating water’s composition, and determining Earth’s mean density.

Host–guest chemistry studies how molecular hosts selectively bind guest species through complementary structures and noncovalent interactions.

A hydrocarbon is a compound composed exclusively of carbon and hydrogen, encompassing major fuels and important raw materials for chemical manufacturing.

Hydrogen is the lightest chemical element, the most abundant element in the universe, and an important industrial feedstock and energy carrier.

A hydrogen bond is a directional attractive interaction involving a bonded hydrogen atom, important in water, biological structures, and molecular assembly.

Hydrolysis is a reaction involving water that cleaves chemical bonds or changes the acid–base behavior of dissolved ions.

The hydrophobic effect is the solvent-mediated tendency of nonpolar molecules or surfaces to associate in water, influencing molecular assembly and biological structure.

Infrared spectroscopy analyzes how matter interacts with infrared radiation to identify substances, investigate molecular vibrations, and measure composition.

An ion is an atom or bonded group of atoms with a net electric charge, involved in chemical bonding, electrical conduction, and biological processes.

Ionization energy is the minimum energy required to remove an electron from an isolated atom, molecule, or ion in a specified state.

Isomerism is the relationship between chemical species with the same molecular formula but different atomic connectivity or spatial arrangement.

Isotopes are forms of the same chemical element that have equal numbers of protons but different numbers of neutrons.

English chemist, physicist, and meteorologist who developed a quantitative atomic theory and the law of partial pressures.

A Lewis structure represents valence electrons, covalent bonds, lone pairs, and formal charges in a molecule or ion.

A ligand is an atom, ion, or molecule that binds to a central atom or molecular target, forming a coordination entity or biological complex.

Limonene is a naturally occurring monoterpene hydrocarbon abundant in citrus peel oils and used in flavorings, fragrances, and solvents.

Linus Pauling was an American chemist and peace activist whose research explained chemical bonding and protein structure and earned him two unshared Nobel Prizes.

Magnesium (Mg, atomic number 12) is a light alkaline-earth metal essential to photosynthesis and cell energy, and widely used in alloys and industry.

Mass spectrometry identifies and quantifies substances by measuring the mass-to-charge ratios and abundances of gas-phase ions.

Methane is the simplest hydrocarbon, a major component of natural gas, and a greenhouse gas produced by biological and geological processes.

Molality expresses the amount of a dissolved substance per kilogram of solvent, providing a mass-based measure of solution composition.

Molar concentration expresses the amount of a specified constituent per unit volume of a solution or mixture.

Molar mass is the mass per unit amount of substance, linking measurable sample masses to quantities of specified chemical entities.

The mole is the SI unit of amount of substance, defined by an exact number of specified elementary entities.

Mole fraction is the amount of one constituent divided by the total amount of all constituents in a mixture.

Molecular orbital theory describes molecular electronic structure using orbitals that can extend across several atoms, explaining bonding, magnetism, and aspects of chemical reactivity.

Molecular recognition is the selective association of molecules through complementary structures and noncovalent interactions.

A molecule is an electrically neutral group of two or more bound atoms, characterized by its composition, structure, and electronic properties.

A monosaccharide is a single carbohydrate unit that serves as a metabolic substrate and a building block of larger carbohydrates.

The Nernst equation relates equilibrium electrochemical potentials to temperature and chemical activities, connecting reaction thermodynamics with cell voltages and ionic equilibrium across membranes.

Nitrogen is the chemical element with atomic number 7, the main constituent of Earth’s atmosphere and an essential component of living organisms.

Nitrogen fixation converts molecular nitrogen into chemically combined forms, supplying essential nutrients through biological, atmospheric, and industrial processes.

The Nobel Prize in Chemistry is an international award established by Alfred Nobel’s will to recognize important chemical discoveries and improvements.

Orbital hybridization describes atomic orbitals as linear combinations that help represent directional bonding and molecular geometry.

Organic chemistry studies the structures, properties, reactions, and synthesis of carbon compounds.

Oxidation state is a formal electron-counting value assigned to an atom to describe its degree of oxidation and track redox changes.

A chemical reaction in which oxidation states change through coupled oxidation and reduction processes.

Oxygen is the chemical element with atomic number 8, a major constituent of air, water, and rocks, and an essential participant in aerobic respiration and combustion.

A peptide bond is an amide linkage joining amino acid residues, forming the backbone of peptides and proteins and constraining their molecular structure.

The periodic table organizes chemical elements by atomic number, revealing recurring patterns in their electronic structures and physical and chemical properties.

pH is a logarithmic measure of hydrogen-ion activity used to describe the acidity or basicity of a solution.

A phosphodiester bond is a phosphate-based covalent linkage that forms the backbone of DNA and RNA and occurs in other biological molecules.

Physical chemistry uses physical laws, mathematical models, and experimental measurements to explain chemical structure, properties, equilibrium, and change.

A pi bond is a covalent bonding interaction with a nodal plane containing the bond axis, commonly formed by sideways overlap of atomic orbitals.

Potassium is a reactive metallic element essential to cellular function and widely used in fertilizers and industrial chemicals.

Powder diffraction characterizes crystalline materials by measuring radiation scattered from many differently oriented crystallites, revealing phase composition, crystal structure, and microstructural properties.

A reaction mechanism describes how reactants become products through elementary chemical events, including bond changes, intermediates, transition states, and the factors governing reaction rates.

The reaction quotient measures a reaction mixture’s composition and, when compared with the equilibrium constant, indicates its thermodynamically favored direction of change.

Relative atomic mass is the dimensionless ratio of an element’s average atomic mass in a specified sample to one twelfth of the mass of a carbon-12 atom.

Resonance describes delocalized chemical bonding through multiple contributing structures that collectively represent a single electronic state.

Reticular chemistry designs and constructs crystalline frameworks by connecting molecular building blocks through strong bonds, enabling systematic control of structure, pores, and chemical functionality.

Ribose is a five-carbon sugar whose D form supplies the sugar component of RNA and numerous biologically important nucleotides.

A sigma bond is a covalent bonding interaction characterized by orbital overlap along the internuclear axis and no nodal plane containing that axis.

Silicon is chemical element 14, a major constituent of Earth’s crust and a semiconductor used in electronics and solar cells.

A solvent is a substance that serves as the dissolving medium of a solution, with properties that influence solubility, chemical reactions, separation processes, and environmental impacts.

A standard state is a conventionally defined reference condition used to express thermodynamic properties, activities, and chemical equilibrium constants.

Stereochemistry studies the three-dimensional arrangement of atoms in chemical species and how that arrangement affects their properties, reactions, and interactions.

Stoichiometry describes the quantitative relationships between reactants and products in chemical reactions.