Dictionary of chemistry

• absolute zero (cryogenics) the lowest temperature theoretically attainable (at which the kinetic energy of atoms and molecules is minimal); 0 Kelvin or 273.15 centigrade or 459.67 Fahrenheit
• acid anhydrides organic compounds that react with water to form an acid
• acidic being or containing an acid; of a solution having an excess of hydrogen atoms (having a pH of less than 7);  being sour to the taste
• actinide series (chemistry) a series of 15 radioactive elements with increasing atomic numbers from actinium to lawrencium
• actinide any of a series of radioactive elements with atomic numbers 89 through 103
• activation energy the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur
• addition reaction a chemical reaction in which one molecule is added to another
• alcohol a liquor or brew containing alcohol as the active agent;  any of a series of volatile hydroxyl compounds that are made from hydrocarbons by distillation
• aldehyde any of a class of highly reactive chemical compounds; used in making resins and dyes and organic acids
• alkali metal any of the monovalent metals of group I of the periodic table (lithium or sodium or potassium or rubidium or cesium or francium)
• alkane a series of non aromatic saturated hydrocarbons with the general formula CnH(2n+2)
• alkene any unsaturated aliphatic hydrocarbon
• alkyl group any of a series of univalent groups of the general formula CnH2n+1 derived from aliphatic hydrocarbons
• alkyne a colorless flammable gas used chiefly in welding and in organic synthesis
• alpha particle a positively charged particle that is the nucleus of the helium atom; emitted from natural or radioactive isotopes
• alpha early testing stage of a software or hardware product; first in order of importance;   the 1st letter of the Greek alphabet;  the beginning of a series or sequence
• amide any organic compound containing the group CONH2
• amine a compound derived from ammonia by replacing hydrogen atoms by univalent hydrocarbon radicals
• amorphous without real or apparent crystalline form;  lacking the system or structure characteristic of living bodies;  having no definite form or distinct shape
• amphiprotic having characteristics of both an acid and a base and capable of reacting as either
• amphoteric having characteristics of both an acid and a base and capable of reacting as either
• amplitude greatness of magnitude;  the property of copious abundance;  (physics) the maximum displacement of a periodic wave
• angular momentum the product of the momentum of a rotating body and its distance from the axis of rotation
• anion a negatively charged ion
• anode a positively charged electrode by which electrons leave an electrical device;  the negatively charged terminal of a voltaic cell or storage battery that supplies current
• antimatter matter consisting of elementary particles that are the antiparticles of those making up normal matter
• aqueous solution a solution in water
• aromatic hydrocarbon a hydrocarbon that contains one or more benzene rings that are characteristic of the benzene series of organic compounds
• arrhenius Swedish chemist and chemist noted for his theory of chemical dissociation (1859 1927)
• atom (nontechnical usage) a tiny piece of anything;  (physics and chemistry) the smallest component of an element having the chemical properties of the element
• atomic mass unit unit of mass for expressing masses of atoms or molecules
• atomic mass (chemistry) the mass (in atomic mass units) of an isotope of an element
• atomic number the order of an element in Mendeleyev's table of the elements; equal to the number of protons in the nucleus or electrons in the neutral state of an atom of an element
• autumn the season when the leaves fall from the trees
• avogadro Italian physicist noted for his work on gases; proposed what has come to be called Avogadro's law (1776 1856)
• balanced total debits and credits are equal;  being in a state of proper balance or equilibrium
• barometer an instrument that measures atmospheric pressure
• bartlett juicy yellow pear;  United States publisher and editor who compiled a book of familiar quotations (1820 1905);  United States explorer who accompanied Peary's expedition to the North Pole and who led many other Arctic trips (1875 1946)
• becquerel French physicist who discovered that rays emitted by uranium salts affect photographic plates (1852 1908)
• beta particle a high speed electron or positron emitted in the decay of a radioactive isotope
• beta preliminary or testing stage of a software or hardware product;  second in order of importance;   the 2nd letter of the Greek alphabet;  beets
• binary compound chemical compound composed of only two elements
• bismuth a heavy brittle diamagnetic trivalent metallic element (resembles arsenic and antimony chemically); usually recovered as a by product from ores of other metals
• blackbody a hypothetical object capable of absorbing all the electromagnetic radiation falling on it
• boltzmann Austrian physicist who contributed to the kinetic theory of gases (1844 1906)
• bomb calorimeter strong sealed vessel for measuring heat of combustion
• borate a salt or ester of boric acid
• born brought into existence;  being talented through inherited qualities;   British nuclear physicist (born in Germany) honored for his contributions to quantum mechanics (1882 1970)
• boyle Irish chemist who established that air has weight and whose definitions of chemical elements and chemical reactions helped to dissociate chemistry from alchemy (1627 1691);  United States writer (1902 1992)
• bragg Confederate general during the American Civil War who was defeated by Grant in the battle of Chattanooga (1817 1876)
• buret measuring instrument consisting of a graduated glass tube with a tap at the bottom; used for titration
• calorimeter a measuring instrument that determines quantities of heat
• calorimetry measurement of quantities of heat
• capillary action a phenomenon associated with surface tension and resulting in the elevation or depression of liquids in capillaries
• carbonate a salt or ester of carbonic acid (containing the anion CO3);  verb treat with carbon dioxide;  turn into a carbonate
• carbonyl group the bivalent radical CO
• carboxylic acid an organic acid characterized by one or more carboxyl groups
• carnot French physicist who founded thermodynamics (1796 1832)
• catalyst something that causes an important event to happen;  (chemistry) a substance that initiates or accelerates a chemical reaction without itself being affected
• cathode ray a beam of electrons emitted by the cathode of an electrical discharge tube
• cathode a negatively charged electrode that is the source of electrons entering an electrical device;  the positively charged terminal of a voltaic cell or storage battery that supplies current
• cation a positively charged ion
• celsius Swedish astronomer who devised the centigrade thermometer (1701 1744)
• chain reaction a series of chemical reactions in which the product of one is a reactant in the next;  a self sustaining nuclear reaction; a series of nuclear fissions in which neutrons released by splitting one atom leads to the splitting of others
• chelate having or resembling chelae or claws;  relating to or characterized by chelation;   a heterocyclic compound having a metal ion attached by coordinate bonds to at least two nonmetal ions;  verb form a chelate, in chemistry
• chemical change (chemistry) any process determined by the atomic and molecular composition and structure of the substances involved
• chemical property a property used to characterize materials in reactions that change their identity
• chemistry the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions;  the way two individuals relate to each other
• chemotherapy the use of chemical agents to treat or control disease (or mental illness)
• ci a unit of radioactivity equal to the amount of a radioactive isotope that decays at the rate of 37,000,000,000 disintegrations per second
• coefficient a constant number that serves as a measure of some property or characteristic
• colloid a mixture with properties between those of a solution and fine suspension
• control rod a steel or aluminum rod that can be moved up or down to control the rate of the nuclear reaction
• coordination compound a compound described in terms of the central atom to which other atoms are bound or coordinated
• corrosion erosion by chemical action;  a state of deterioration in metals caused by oxidation or chemical action
• covalent bond a chemical bond that involves sharing a pair of electrons between atoms in a molecule
• crenation one of a series of rounded projections (or the notches between them) formed by curves along an edge (as the edge of a leaf or piece of cloth or the margin of a shell or a shriveled red blood cell observed in a hypertonic solution etc.)
• crick English biochemist who (with Watson in 1953) helped discover the helical structure of DNA (1916 2004);  a painful muscle spasm especially in the neck or back (`rick' and `wrick' are British); verb twist (a body part) into a strained position
• critical mass the minimum mass of fissionable material that can sustain a chain reaction;  the minimum amount (of something) required to start or maintain a venture
• critical point a crisis situation or point in time when a critical decision must be made
• cubic centimeter a metric unit of volume equal to one thousandth of a liter
• cubic meter a metric unit of volume or capacity equal to 1000 liters
• d the 4th letter of the Roman alphabet;  a fat soluble vitamin that prevents rickets
• da an official prosecutor for a judicial district
• dalton English chemist and physicist who formulated atomic theory and the law of partial pressures; gave the first description of red green color blindness (1766 1844)
• davy English chemist who was a pioneer in electrochemistry and who used it to isolate elements sodium and potassium and barium and boron and calcium and magnesium and chlorine (1778 1829)
• de broglie French nuclear physicist who generalized the wave particle duality by proposing that particles of matter exhibit wavelike properties (1892 1987)
• density the amount per unit size;  the spatial property of being crowded together
• diamagnetic relating to or exhibiting diamagnetism; slightly repelled by a magnet
• diamagnetism phenomenon exhibited by materials like copper or bismuth that become magnetized in a magnetic field with a polarity opposite to the magnetic force; unlike iron they are slightly repelled by a magnet
• diffraction when light passes sharp edges or goes through narrow slits the rays are deflected and produce fringes of light and dark bands
• dilution weakening (reducing the concentration) by the addition of water or a thinner;  a diluted solution
• dipole moment the moment of a dipole
• dispersed phase (of colloids) a substance in the colloidal state
• dispersion medium (of colloids) a substance in which another is colloidally dispersed
• double bond a covalent bond in which two pairs of electrons are shared between two atoms
• dry cell a small Leclanche cell containing no free liquid; the electrolyte is a paste and the negative zinc pole forms the container of the cell; used in flashlights, portable radios, etc.
• ea the Babylonian god of wisdom; son of Apsu and father of Marduk; counterpart of the Sumerian Enki; as one of the supreme triad including Anu and Bel he was assigned control of the watery element
• effusion flow under pressure;  an unrestrained expression of emotion
• electrolysis removing superfluous or unwanted hair by passing an electric current through the hair root;  (chemistry) a chemical decomposition reaction produced by passing an electric current through a solution containing ions
• electrolyte a solution that conducts electricity
• electrolytic cell a cell containing an electrolyte in which an applied voltage causes a reaction to occur that would not occur otherwise (such as the breakdown of water into hydrogen and oxygen)
• electromagnetic radiation radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge
• electromagnetic spectrum the entire frequency range of electromagnetic waves
• electron volt a unit of energy equal to the work done by an electron accelerated through a potential difference of 1 volt
• electron an elementary particle with negative charge
• electronegativity (chemistry) the tendency of an atom or radical to attract electrons in the formation of an ionic bond
• elements violent or severe weather (viewed as caused by the action of the four elements)
• empirical formula a chemical formula showing the ratio of elements in a compound rather than the total number of atoms
• emulsion a light sensitive coating on paper or film; consists of fine grains of silver bromide suspended in a gelatin;  (chemistry) a colloid in which both phases are liquids
• end point a place where something ends or is complete;  the final point in a process
• enthalpy (thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure
• entropy (thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work;  (communication theory) a numerical measure of the uncertainty of an outcome
• equilibrium constant (chemistry) the ratio of concentrations when equilibrium is reached in a reversible reaction (when the rate of the forward reaction equals the rate of the reverse reaction)
• ester formed by reaction between an acid and an alcohol with elimination of water
• ev a unit of energy equal to the work done by an electron accelerated through a potential difference of 1 volt
• ex out of fashion;   the 24th letter of the Roman alphabet; a woman who was formerly a particular man's wife;  a man who was formerly a certain woman's husband
• fahrenheit German physicist who invented the mercury thermometer and developed the scale of temperature that bears his name (1686 1736)
• faraday the English physicist and chemist who discovered electromagnetic induction (1791 1867)
• fcc an independent government agency that regulates interstate and international communications by radio and television and wire and cable and satellite
• first law of thermodynamics the fundamental principle of physics that the total energy of an isolated system is constant despite internal changes
• fissile capable of being split or cleft or divided in the direction of the grain;  capable of undergoing nuclear fission
• fission a nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy; reproduction of some unicellular organisms by division of the cell into two more or less equal parts
• fissionable capable of undergoing nuclear fission
• free radical an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule than has lost an electron and will stabilize itself by stealing an electron from a nearby molecule
• freezing point the temperature below which a liquid turns into a solid
• freezing the withdrawal of heat to change something from a liquid to a solid
• frequency the number of observations in a given statistical category;  the ratio of the number of observations in a statistical category to the total number of observations;  the number of occurrences within a given time period
• fuel cell cell that produces electricity by oxidation of fuel (hydrogen and oxygen or zinc and air); for use in electric cars
• fuller a workman who fulls (cleans and thickens) freshly woven cloth for a living;  United States architect who invented the geodesic dome (1895 1983);  United States jurist and chief justice of the United States Supreme Court (1833 1910)
• galvanization either the work of covering with metal by the use of a galvanic current or the coating of iron with zinc to protect it from rusting;  stimulation that arouses a person to lively action; stimulation with a galvanic current
• gamma ray electromagnetic radiation emitted during radioactive decay and having an extremely short wavelength
• gay lussac French chemist and physicist who first isolated boron and who formulated the law describing the behavior of gases under constant pressure (1778 1850)
• geiger counter counter tube that detects ionizing radiations
• geiger German physicist who developed the Geiger counter (1882 1945)
• gel a colloid in a more solid form than a sol;  a thin translucent membrane used over stage lights for color effects;  verb become a gel;  apply a styling gel to
• gibbs United States chemist (1839 1903)
• gravimetric analysis quantitative analysis by weight
• ground state (physics) the lowest energy state of an atom or other particle
• haber process an industrial process for producing ammonia from nitrogen and hydrogen by combining them under high pressure in the present of an iron catalyst
• half life the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
• halide a salt of any halogen acid
• halogen any of five related nonmetallic elements (fluorine or chlorine or bromine or iodine or astatine) that are all monovalent and readily form negative ions
• hemolysis lysis of erythrocytes with the release of hemoglobin
• huygens Dutch physicist who first formulated the wave theory of light (1629 1695)
• hybridization (genetics) the act of mixing different species or varieties of animals or plants and thus to produce hybrids
• hydrate any compound that contains water of crystallization; verb cause to be hydrated; add water or moisture to;  become hydrated and combine with water;  supply water or liquid to in order to maintain a healthy balance
• hydrocarbon an organic compound containing only carbon and hydrogen
• hydrogen carbonate a salt of carbonic acid (containing the anion HCO3) in which one hydrogen atom has been replaced; an acid carbonate
• hydrogenation a chemical process that adds hydrogen atoms to an unsaturated oil
• hydroxide a chemical compound containing the hydroxyl group;  a compound of an oxide with water
• hypertonic (of a solution) having a higher osmotic pressure than a comparison solution;  (of living tissue) in a state of abnormally high tension
• hypotonic (of a solution) having a lower osmotic pressure than a comparison solution;  (of living tissue) lacking normal tone or tension
• hz the unit of frequency; one hertz has a periodic interval of one second
• i the 9th letter of the Roman alphabet;  a nonmetallic element belonging to the halogens; used especially in medicine and photography and in dyes; occurs naturally only in combination in small quantities (as in sea water or rocks)
• ideal gas a hypothetical gas with molecules of negligible size that exert no intermolecular forces
• immiscible (chemistry, physics) incapable of mixing
• inert gas any of the chemically inert gaseous elements of the helium group in the periodic table
• insoluble without hope of solution;  (of a substance) incapable of being dissolved;  admitting of no solution or explanation
• ion a particle that is electrically charged (positive or negative); an atom or molecule or group that has lost or gained one or more electrons
• ionic bond a chemical bond in which one atom loses an electron to form a positive ion and the other atom gains to electron to form a negative ion
• ionizing radiation high energy radiation capable of producing ionization in substances through which it passes
• isomorphous having similar appearance but genetically different
• j the 10th letter of the Roman alphabet;  a unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second
• ka unknown god; an epithet of Prajapati and Brahma
• kb a unit of information equal to one thousand (1024) bytes
• kelvin British physicist who invented the Kelvin scale of temperature and pioneered undersea telegraphy (1824 1907);  the basic unit of thermodynamic temperature adopted under the Systeme International d'Unites
• ketone any of a class of organic compounds having a carbonyl group linked to a carbon atom in each of two hydrocarbon radicals
• kg one thousand grams; the basic unit of mass adopted under the Systeme International d'Unites
• kilogram one thousand grams; the basic unit of mass adopted under the Systeme International d'Unites
• kinetic energy the mechanical energy that a body has by virtue of its motion
• kw a unit of power equal to 1000 watts
• lanthanide series the rare earth elements with atomic numbers 57 through 71; having properties similar to lanthanum
• lanthanide any element of the lanthanide series (atomic numbers 57 through 71)
• lavoisier French chemist known as the father of modern chemistry; discovered oxygen and disproved the theory of phlogiston (1743 1794)
• law of conservation of matter a fundamental principle of classical physics that matter cannot be created or destroyed in an isolated system
• ligand an atom or molecule or radical or ion that forms a complex around a central atom
• line spectrum a spectrum in which energy is concentrated at particular wavelengths; produced by excited atoms and ions as they fall back to a lower energy level
• liter a metric unit of capacity equal to the volume of 1 kilogram of pure water at 4 degrees centigrade and 760 mm of mercury (or approximately 1.76 pints)
• london the capital and largest city of England; located on the Thames in southeastern England; financial and industrial and cultural center;  United States writer of novels based on experiences in the Klondike gold rush (1876 1916)
• m the 13th letter of the Roman alphabet;  concentration measured by the number of moles of solute per liter of solution;  the basic unit of length adopted under the Systeme International d'Unites (approximately 1.094 yards)
• magic number the atomic number of an extra stable strongly bound atomic nucleus: 2, 8, 20, 28, 50, 82 or 126
• manometer a pressure gauge for comparing pressures of a gas
• mass defect the amount by which the mass of an atomic nucleus is less than the sum of the masses of its constituent particles
• mass number the sum of the number of neutrons and protons in an atomic nucleus
• melting point the temperature below which a liquid turns into a solid
• melting becoming liquid;   the process whereby heat changes something from a solid to a liquid
• mendeleev Russian chemist who developed a periodic table of the chemical elements and predicted the discovery of several new elements (1834 1907)
• metalloid of or being a nonmetallic element that has some of the properties of metal
• millicurie a unit of radioactivity equal to one thousandth of a curie
• millikan United States physicist who isolated the electron and measured its charge (1868 1953)
• milliliter a metric unit of volume equal to one thousandth of a liter
• miscible (chemistry, physics) capable of being mixed
• ml a metric unit of volume equal to one thousandth of a liter
• molality concentration measured by the number of moles of solute per kilogram of solvent
• molarity concentration measured by the number of moles of solute per liter of solution
• molecular formula a chemical formula based on analysis and molecular weight
• molecule (physics and chemistry) the simplest structural unit of an element or compound;  (nontechnical usage) a tiny piece of anything
• na a silvery soft waxy metallic element of the alkali metal group; occurs abundantly in natural compounds (especially in salt water); burns with a yellow flame and reacts violently in water; occurs in sea water and in the mineral halite (rock salt)
• neutralization reaction a chemical reaction in which an acid and a base interact with the formation of a salt; with strong acids and bases the essential reaction is the combination of hydrogen ions with hydroxyl ions to form water
• neutron an elementary particle with 0 charge and mass about equal to a proton; enters into the structure of the atomic nucleus
• nitrate any compound containing the nitrate group (such as a salt or ester of nitric acid);  verb treat with nitric acid, so as to change an organic compound into a nitrate
• nitrogen fixation the assimilation of atmospheric nitrogen by soil bacteria and its release for plant use on the death of the bacteria
• noble gas any of the chemically inert gaseous elements of the helium group in the periodic table
• nomenclature a system of words used to name things in a particular discipline
• nonmetal not containing or resembling or characteristic of a metal;   a chemical element lacking typical metallic properties
• nuclear chemistry the chemistry of radioactive substances
• nuclear fuel fuel (such as uranium) that can be used in nuclear reactors as a source of electricity
• nuclear reaction (physics) a process that alters the energy or structure or composition of atomic nuclei
• nuclear reactor (physics) any of several kinds of apparatus that maintain and control a nuclear reaction for the production of energy or artificial elements
• nucleon a constituent (proton or neutron) of an atomic nucleus
• oct the month following September and preceding November
• or a room in a hospital equipped for the performance of surgical operations;  a state in northwestern United States on the Pacific
• organic compound any compound of carbon and another element or a radical
• osmosis diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal
• osmotic pressure (physical chemistry) the pressure exerted by a solution necessary to prevent osmosis into that solution when it is separated from the pure solvent by a semipermeable membrane
• overlap the property of partial coincidence in time;  a representation of common ground between theories or phenomena; a flap that lies over another part;  verb coincide partially or wholly; extend over and cover a part of
• oxidant a substance that oxidizes another substance
• oxidation number the degree of oxidation of an atom or ion or molecule; for simple atoms or ions the oxidation number is equal to the ionic charge
• oxidation reduction a reversible chemical reaction in which one reaction is an oxidation and the reverse is a reduction
• oxidation the process of oxidizing; the addition of oxygen to a compound with a loss of electrons; always occurs accompanied by reduction
• oxidizing agent a substance that oxidizes another substance
• oxyacid any acid that contains oxygen
• paramagnetism materials like aluminum or platinum become magnetized in a magnetic field but it disappears when the field is removed
• particle accelerator a scientific instrument that increases the kinetic energy of charged particles
• particle a function word that can be used in English to form phrasal verbs;  a body having finite mass and internal structure but negligible dimensions;  (nontechnical usage) a tiny piece of anything
• pauli exclusion principle no two electrons or protons or neutrons in a given system can be in states characterized by the same set of quantum numbers
• pauling United States chemist who studied the nature of chemical bonding (1901 1994)
• periodic law (chemistry) the principle that chemical properties of the elements are periodic functions of their atomic numbers
• periodic table a tabular arrangement of the chemical elements according to atomic number as based on the periodic law
• photon a quantum of electromagnetic radiation; an elementary particle that is its own antiparticle
• photosynthesis synthesis of compounds with the aid of radiant energy (especially in plants)
• physical change a change from one state (solid or liquid or gas) to another without a change in chemical composition
• physical property a property used to characterize physical objects
• polymorph an organism that can assume more than one adult form as in the castes of ants or termites
• positron an elementary particle with positive charge; interaction of a positron and an electron results in annihilation
• potential energy the mechanical energy that a body has by virtue of its position; stored energy
• pounds per square inch a unit of pressure
• precision the quality of being reproducible in amount or performance
• primary cell an electric cell that generates an electromotive force by an irreversible conversion of chemical to electrical energy; cannot be recharged
• proton a stable particle with positive charge equal to the negative charge of an electron
• psi the 23rd letter of the Greek alphabet;  a unit of pressure
• q the 17th letter of the Roman alphabet
• quantitative analysis chemical analysis to determine the amounts of each element in the substance
• quantization the act of dividing into quanta or expressing in terms of quantum theory
• quantum mechanics the branch of quantum physics that accounts for matter at the atomic level; an extension of statistical mechanics based on quantum theory (especially the Pauli exclusion principle)
• radiation therapy (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance
• radioactive decay the spontaneous disintegration of a radioactive substance along with the emission of ionizing radiation
• radioactivity the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
• radiocarbon dating a chemical analysis used to determine the age of organic materials based on their content of the radioisotope carbon 14; believed to be reliable up to 40,000 years
• radioisotope a radioactive isotope of an element; produced either naturally or artificially
• reactant a chemical substance that is present at the start of a chemical reaction
• redox a reversible chemical reaction in which one reaction is an oxidation and the reverse is a reduction
• reducing agent a substance capable of bringing about the reduction of another substance as it itself is oxidized; used in photography to lessen the density of a negative or print by oxidizing some of the slackened silver
• reductant a substance capable of bringing about the reduction of another substance as it itself is oxidized; used in photography to lessen the density of a negative or print by oxidizing some of the slackened silver
• reduction the act of reducing complexity;  any process in which electrons are added to an atom or ion (as by removing oxygen or adding hydrogen); always occurs accompanied by oxidation of the reducing agent;  the act of decreasing or reducing something
• reversible process any process in which a system can be made to pass through the same states in the reverse order when the process is reversed
• rounding (mathematics) a miscalculation that results from rounding off numbers to a convenient number of decimals
• rydberg a wave number characteristic of the wave spectrum of each element
• schematic represented in simplified or symbolic form;  diagram of an electrical or mechanical system
• scientific method a method of investigation involving observation and theory to test scientific hypotheses
• scintillation counter counter tube in which light flashes when exposed to ionizing radiation
• second law of thermodynamics a law stating that mechanical work can be derived from a body only when that body interacts with another at a lower temperature; any spontaneous process results in an increase of entropy
• secondary cell a cell that can be recharged
• semipermeable membrane a membrane (as a cell membrane) that allows some molecule to pass through but not others
• silicate a salt or ester derived from silicic acid
• soddy English chemist whose work on radioactive disintegration led to the discovery of isotopes (1877 1956);  a house built of sod or adobe laid in horizontal courses
• solomon (Old Testament) son of David and king of Israel noted for his wisdom (10th century BC)
• soluble (of a substance) capable of being dissolved in some solvent (usually water);  susceptible of solution or of being solved or explained
• solute the dissolved substance in a solution; the component of a solution that changes its state
• solvation a chemical process in which solvent molecules and molecules or ions of the solute combine to form a compound
• solvent capable of meeting financial obligations;   a liquid substance capable of dissolving other substances;  a statement that solves a problem or explains how to solve the problem
• space lattice a 3 dimensional geometric arrangement of the atoms or molecules or ions composing a crystal
• standing wave a wave (as a sound wave in a chamber or an electromagnetic wave in a transmission line) in which the ratio of its instantaneous amplitude at one point to that at any other point does not vary with time
• stoichiometry (chemistry) the relation between the quantities of substances that take part in a reaction or form a compound (typically a ratio of whole integers)
• stp standard temperature and pressure
• structural formula an expanded molecular formula showing the arrangement of atoms within the molecule
• sublimation (psychology) modifying the natural expression of an impulse or instinct (especially a sexual one) to one that is socially acceptable;  (chemistry) a change directly from the solid to the gaseous state without becoming liquid
• sulfate a salt or ester of sulphuric acid;  verb convert into a sulfate
• superoxide the univalent anion O2 ;  a metallic oxide containing the univalent anion O2
• supersaturated being more concentrated than normally possible and therefore not in equilibrium
• surface tension a phenomenon at the surface of a liquid caused by intermolecular forces
• surroundings the area in which something exists or lives; the environmental condition
• temperature the degree of hotness or coldness of a body or environment (corresponding to its molecular activity);  the somatic sensation of cold or heat
• thermochemistry the branch of chemistry that studies the relation between chemical action and the amount of heat absorbed or generated
• third law of thermodynamics law stating that the entropy of a substance approaches zero as its temperature approaches absolute zero
• tl a soft grey malleable metallic element that resembles tin but discolors on exposure to air; it is highly toxic and is used in rodent and insect poisons; occurs in zinc blende and some iron ores
• torr a unit of pressure equal to 0.001316 atmosphere; named after Torricelli
• transmutation an act that changes the form or character or substance of something;  (physics) the change of one chemical element into another (as by nuclear decay or radioactive bombardment);  a qualitative change
• tyndall effect the phenomenon in which light is scattered by very small particles in its path; it makes a beam of light visible; the scattered light is mainly blue
• uncertainty being unsettled or in doubt or dependent on chance;  the state of being unsure of something
• unit cell the smallest group of atoms or molecules whose repetition at regular intervals in three dimensions produces the lattices of a crystal
• unsaturated (of color) not chromatically pure; diluted;  used of a compound (especially of carbon) containing atoms sharing more than one valence bond;  not saturated; capable of dissolving more of a substance at a given temperature
• vacancy being unoccupied;  an empty area or space
• vapor pressure the pressure exerted by a vapor; often understood to mean saturated vapor pressure (the vapor pressure of a vapor in contact with its liquid form)
• vaporization annihilation by vaporizing something;  the process of becoming a vapor
• vector a variable quantity that can be resolved into components;  any agent (person or animal or microorganism) that carries and transmits a disease;  a straight line segment whose length is magnitude and whose orientation in space is direction
• viscosity resistance of a liquid to sheer forces (and hence to flow)
• voltaic pertaining to or producing electric current by chemical action;   a group of Niger Congo languages spoken primarily in southeastern Mali and northern Ghana
• wavelength the distance (measured in the direction of propagation) between two points in the same phase in consecutive cycles of a wave;  a shared orientation leading to mutual understanding
• wilkins English biochemist who helped discover the structure of DNA (born in 1916);  Australian who was the first to explore the Arctic by airplane (1888 1958);  United States civil rights leader (1901 1981)

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