Category: Chemistry Dictionary

Zinc : A metallic chemical element with atomic number 30 and symbol Zn.

Zwitterion : A chemical compound whose net charge is zero and hence is electrically neutral. But there are some positive and negative charges in it, due to the formal charge, owing to the partial charges of its constituent atoms.

Zone melting : A way to remove impurities from an element by melting it and slowly travel down an ingot (cast).

X-ray diffraction : a method for establishing structures of crystalline solids using single wavelength X-rays and looking at diffraction pattern.

X-ray photoelectron spectroscopy : A spectroscopic technique used to measure the composition of a material.

Yield : The quantifiable amount of product produced during a chemical reaction.

X-ray : A form of ionizing, electromagnetic radiation between gamma and UV rays in the electromagnetic spectrum.

Work-up : The series of manipulations required to isolate and purify the desired product or products of a chemical reaction.

Wet chemistry : Also bench chemistry or classical chemistry.

A form of analytical chemistry which uses classical laboratory methods such as simple observation and elementary chemical tests to study chemicals and chemical reactions, i.e. without the use of sophisticated instruments or automated or computerized analysis. It is often used in schools to teach the principles of chemistry to students.

Wave function : A mathematical function describing the position of an electron in a three-dimensional space.

Water : A polar inorganic compound with the chemical formula H₂O that is a tasteless, odorless, and generally colorless liquid at standard temperature and pressure, though it also occurs naturally as a solid  and a gas at the Earth’s surface. It is the most abundant substance on Earth and therefore an integral component of virtually all chemical and biological systems. Water is often described as the “universal solvent” for its inherent ability to dissolve many substances.

Watch glass : A circular, concave piece of glass commonly used in chemistry laboratories as a working surface for various purposes, such as evaporating liquids, holding solids while they are being weighed, heating small amounts of a substance, or as a cover for a beaker.

Volumetric analysis : See titration.

Volume : The quantity of three-dimensional space enclosed by a closed surface, or the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains. The SI unit for volume is the cubic metre (m³).

Voltmeter : An instrument that measures electrical cell potential.

Viscosity : A measure of the resistance of a liquid to flow.

Volatility : A material quality which describes how readily a substance vaporizes. At a given temperature and pressure, a substance with high volatility is more likely to exist as a gas, while a substance with low volatility is more likely to exist as a liquid or solid; equivalently, less volatile substances will more readily condense from a gaseous state than highly volatile ones.

Volt (V) : A derived unit of electric potential, electric potential difference, and electromotive force, defined as one joule of work per coulomb.

Vaporization : Also boiling.

The phase transition of a substance from a liquid to a gas.

Vapor pressure : Also equilibrium vapor pressure.

The pressure exerted by a vapor which is in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. It is commonly described as the tendency of particles to spontaneously escape from the liquid or solid state into the gaseous state and is used as an indication of a liquid’s evaporation rate.

Vapor : When a substance is below the critical temperature while in the gas phase.

Van der Waals force : One of the forces (attraction/repulsion) between molecules.

Valency : The combining capacity of an element.

Van ‘t Hoff factor : The ratio of moles of particles in solution to moles of solute dissolved.

Valence bond theory : A theory explaining the chemical bonding within molecules by discussing valencies, the number of chemical bonds formed by an atom.

Valence electron : Any of the outermost electrons of an atom, which are located in electron shells.

Vacuum flask : Also Dewar flask or thermos.

A storage vessel consisting of two flasks or other containers, placed one within the other and joined at the neck, and a space in between that is partially evacuated of air, creating a near-vacuum that significantly reduces the transfer of heat between the vessel’s interior and its ambient environment. Vacuum flasks can greatly lengthen the time over which their contents remain warmer or cooler than the ambient environment.

Unit factor : Statements used in converting between units.

Unified atomic mass unit (u) : Also Dalton (Da).

A unit of mass approximately equal to the mass of one proton or neutron. It is sometimes equated with the technically distinct and obsolete atomic mass unit and abbreviated amu.

Unit cell : The smallest repeating unit of a crystalline lattice.

Uncertainty principle : Knowing the location of a particle makes the momentum uncertain, while knowing the momentum of a particle makes the location uncertain.

Uncertainty : The notion that any measurement that involves estimation of any amount cannot be exactly reproducible.

UN number : A four-digit code used to note hazardous and flammable substances.

Tyndall effect : The effect of light scattering by colloidal or suspended particles.

Triple point : The place where temperature and pressure of three phases are the same. Water has a special phase diagram.

Triple bond : A bond that involves the covalent sharing of three pairs of electrons (for example, the diatomic nitrogen molecule, N₂, is composed of two nitrogen atoms linked by a triple bond).

Transition metal : An element whose atoms naturally occur with incompletely filled “d” sub-shells. These elements are grouped as the so-called d-block elements in the periodic table.

Transuranic element : Any element with an atomic number greater than 92 (i.e. occurring after uranium in the periodic table). None of the transuranic elements are stable in natural conditions.

Titration : Also titrimetry or volumetric analysis.

A laboratory method of quantitative chemical analysis that is used to determine the concentration of an identified analyte. The procedure involves preparing a particular reagent as a standard solution of known concentration and volume (called the titrant or titrator) and allowing it to react with a solution of the analyte (called the titrand) to determine the latter’s concentration.

Torr : A unit for measuring pressure, equivalent to 133.322 Pa or 1.3158×10⁻³ atm.

Thermometer : An instrument used to measure temperature.

Thermodynamic stability : The condition of a system being in its lowest energy state with its environment (equilibrium).

Thermodynamics : The study of the effects of changing temperature, volume or pressure (or work, heat, and energy) on a macroscopic scale.

Thermochemistry : The study of the absorption or release of heat during a chemical reaction.

Theoretical yield : See yield.

Thermal conductivity : The property of a material that allows it to conduct thermal energy or heat (a quantity often denoted by k {\displaystyle k} ).

Suspension : A heterogeneous mixture that contains solid particles which are sufficiently large for sedimentation to occur, by which such particles separate from and settle out of the fluid over time if left undisturbed. In a suspension, the solute does not dissolve but remains dispersed or suspended throughout the fluid solvent only transiently and with mechanical agitation. Contrast colloid and solution.

Temperature : A proportional measure of the average kinetic energy of the random motions of the constituent microscopic particles of a system. The SI base unit for temperature is the kelvin.

Substance : See chemical substance.

Sublimation : The phase transition of a substance from a solid to a limewater fuel or gas without an apparent intervening transition to a liquid in the process.

Structural isomer : Also constitutional isomer.

Subatomic particle : Any particle that is smaller than an atom. Examples include protons, neutrons, and electrons.

Stereoisomer : Also spatial isomer.

An isomer which possesses an identical chemical composition but which differs in the spatial arrangement of its atoms.

Stoichiometry : The calculation of quantities of reactants and products in chemical reactions. Stoichiometry is based on the law of conservation of mass and the observation that quantities of reactants and products typically exist in ratios of positive integers, implying that if the amounts of the separate reactants are known, then the amounts of the products can be calculated.

Standard conditions of temperature and pressure (STP) : A standardisation of ambient temperature and pressure used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation STP or SATP.

State of matter : The condition of matter existing in a distinct, homogeneous, macroscopic form. Solid, liquid, gas, and plasma are the four traditional states of matter and the most well-known. See also phase.

Spectroscopy : The study of radiation and matter, such as X-ray absorption and emission spectroscopy.

Spectrometry : See mass spectrometry.

Solution : A homogeneous mixture made up of multiple substances generally referred to as solutes and solvents

Solvation : See dissolution.

Solute : The part of a solution that is dissolved into the solvent. For example, sodium chloride (NaCl) is the solute in a solution of saline water.

Solubility : The property of a solid, liquid, or gaseous solute to dissolve in a solid, liquid, or gaseous solvent. It is typically expressed as the proportion of solute dissolved in the solvent in a saturated solution

Solid : One of the four fundamental states of matter, characterized by relatively low-energy particles packed closely together in rigid structures with definite shape and volume. See Young’s modulus.

Sol : A suspension of solid particles in a liquid. Artificial examples include sol-gels.

Side chain : A chemical substituent group that is attached to the core part or “backbone” of a larger molecule, especially an oligomeric or polymeric hydrocarbon chain that branches off of the longer primary chain of a macromolecule, as used in biochemistry and organic chemistry.

Single bond : A bond that involves the sharing of one pair of electrons.

Schrödinger equation : A quantum state equation which represents the behaviour of an electron around an atom.

Salt bridge : A device used to connect reduction with oxidation half-cells in an electrochemical cell.

Saline solution : A common term for a solution of sodium chloride (NaCl) dissolved in water (H₂O).

S-block : The collective name for the elements in Groups 1 and 2 of the periodic table (the alkali and alkaline metals), as well as hydrogen and helium.

Salt : Any ionic compound composed of one or more anions and one or more cations.

Reagent : Also another name for a reactant.

A test substance that is added to a system in order to bring about a chemical reaction, or to see whether a reaction occurs.

Retort : A laboratory apparatus used for the distillation or dry distillation of chemical substances, traditionally consisting of a spherical vessel with a long, downward-pointing neck that conducts the condensed vapors produced by distillation into a separate collection vessel.

Reactivity series : Also activity series.

An empirical, calculated, and structurally analytical progression of a series of metals, arranged by their general reactivity from highest to lowest and used to summarize information about their reactions with acids and water and the methods used to extract them from ores.

Reactive intermediate : Also simply called an intermediate.

Reaction rate : The speed at which reactants are converted into products in a chemical reaction.

Reaction mechanism : The step-by-step sequence of elementary reactions by which a larger chemical reaction or overall change occurs. A complete mechanism must describe and explain which bonds are broken and which are formed (and in what order), as well as all reactants, products, and catalysts involved; the amounts of each; all intermediates, activated complexes, and transition states; and the stereochemistry of each chemical species. Because the detailed processes of a complex reaction are not observable in most cases, a reaction mechanism is often a theoretical conjecture based on thermodynamic feasibility and what little support can be gained from experiment.

Reactant : Sometimes used interchangeably with reagent.

Any substance that is consumed in the course of a chemical reaction.

Rate equation : Also rate law.

Radioactive decay : The process of an unstable atomic nucleus losing energy by emitting radiation.

Raoult’s law : A law of thermodynamics which states that the partial pressure of each gaseous component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its molar fraction in the mixture.

Radiation : Energy released in the form of waves or subatomic particles when there is a change from high-energy to low-energy states.

Racemate : An equimolar mixture of a pair of enantiomers which does not exhibit optical activity. The chemical name or formula of a racemate is distinguished from those of the enantiomers by the prefix (±)- or by the symbols RS and SR.

Quantum : pl. quanta

Quark : An elementary particle and a fundamental constituent of matter.

Quantum mechanics : The study of how atoms, molecules, subatomic particles, etc. behave and are structured.

Pure substance : See chemical substance.

Pyrolysis : The thermal decomposition of materials at elevated temperatures in an inert atmosphere such as a vacuum gas.

Proton : A subatomic particle with a positive electric charge that is found in the nucleus of an atom. Often denoted with the symbol H⁺.

Protonation : The addition of a proton (H⁺) to an atom, molecule, or ion.

Polyatomic ion : A molecule composed of two or more covalently bonded atoms which collectively bear a net electric charge and therefore act as an ion.

Pressure : The force applied perpendicular to the surface of an object per unit area. The SI unit for pressure is the pascal (Pa), though many other units of pressure are also commonly used in chemistry.

Photon : A carrier of electromagnetic radiation of all wavelengths (such as gamma rays and radio waves).

Precipitate : The formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid.

Potential energy : The stored energy in a body or in a system due to its position in a force field or due to its configuration.

Oxidation state : Also oxidation number.

1.  The degree of oxidation of an individual atom in a chemical compound, measured as the decrease in the number of electrons relative to the atom’s naturally occurring elemental state.2.  The hypothetical electric charge (positive, negative, or zero) that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component.

Periodic table of the elements: Also simply called the periodic table.

A tabular arrangement of the chemical elements organized by their atomic number, electron configuration, and other chemical properties, whose adopted structure shows periodic trends and is used by chemists to derive relationships between various elements as well as predict the properties and behaviors of undiscovered or newly synthesized elements. The first periodic table of the elements was published by Russian chemist Dmitri Mendeleev in 1869.

Period : A horizontal row of the periodic table of the elements and the elements that share it. Contrast group.

Plasma : One of the four fundamental states of matter, in which very high-energy particles are partially or fully ionized to the point that they display unique properties and behaviors unlike those of the other three states. Plasma does not exist freely on the Earth’s surface under natural conditions.

Pipette : Also spelled pipet.

A laboratory tool commonly used in chemistry, biology, and medicine to transfer and dispense a precisely measured volume of liquid.