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Chemistry glossary, chemistry dictionary, definition of chemistry terms, meanings of chemistry terms, chemistry notes, chemistry guesspapers, chemistry free

analyte
An analyte is the sample constituent whose concentration is sought in a chemical analysis
anode.  Compare with cathode
The electrode at which oxidation occurs in a cell. Anions migrate to the anode.
aqueous.  (aq) aqueous solution.
A substance dissolved in water.
balanced equation. balanced.
A description of a chemical reaction that gives the chemical formulas of the reactants and the products of the reaction, with coefficients introduced so that the number of each type of atom and the total charge is unchanged by the reaction. For example, a balanced equation for the reaction of sodium metal (Na(s)) with chlorine gas (Cl2(g)) to form table salt (NaCl(s)) would be 2 Na(s) + Cl2(g) = 2 NaCl(s), NOT Na(s) + Cl2(g) = NaCl(s).
Brösted acid. Compare with acid.
A material that gives up hydrogen ions in a chemical reaction.
Brösted base. Compare with base
A material that accepts hydrogen ions in a chemical reaction.
catalyst. catalyze; catalysis.
A substance that increases the rate of a chemical reaction, without being consumed or produced by the reaction. Catalysts speed both the forward and reverse reactions, without changing the position of equilibrium. Enzymes are catalysts for many biochemical reactions.
cation. Compare with anion.
A cation is a positively charged ion. Metals typically form cations.
chemical change. reaction; chemical reaction. Compare with physical change.
A chemical change is a dissociation, recombination, or rearrangement of atoms.
chemical equation.
A compact notation for describing a chemical change. The formulas of the reactantsare added together on the left hand side of the equation; the formulas of the products are added together on the right side. Coefficients are inserted before the formulas to ensure that the equation is balanced. The phase in which each substance is found is usually indicated in parentheses after each formula. For example, 2 H2(g) + O2(g) = 2 H2O(g) indicates that 2 moles of hydrogen gas combine with one mole of oxygen gas to produce two moles of steam.
combination reaction.
A reaction in which two or more substances are chemically bonded together to produce a product. For example, 2 Na(s) + Cl2(g)  2 NaCl(s) is a combination reaction.
combustion. combustion reaction.
A chemical reaction between a fuel and an oxidizing agent  that produces heat (and usually, light). For example, the combustion of methane is represented as CH4(g) + 2 O2(g) = CO2(g) + 2 H2O().
complete ionic equation. total ionic equation. Compare with net ionic equation.
A balanced equation that describes a reaction occurring in solution, in which all strong electrolytes are written as dissociated ions.
compound  Compare with element and mixture.
A compound is a material formed from elements chemically combined in definite proportions by mass. For example, water is formed from chemically bound hydrogen and oxygen. Any pure water sample contains 2 g of hydrogen for every 16 g of oxygen.
decomposition. decompose; decomposable; decomposition reaction. Compare with synthesis.
A reaction in which a compound is broken down into simpler compounds or elements. Compounds sometimes decompose if heated strongly or if subjected to a strong electric current (electrolysis).
Displacement. displacement reaction; replacement reaction; replacement.
A reaction in which a fragment of one reactant is replaced by another reactant (or by a fragent of another reactant). Displacement reactions have the same number of products as reactants, and are described by equations of the form A + BC  AB + C (single displacement) or AB + CD  AC + BD (double displacement).
double displacement. double displacement reaction; double replacement; double replacement reaction; double exchange; exchange; metathesis.
A double displacement or metathesis is a reaction in which two reactants trade fragments:
AB + CD = AC + BD
Most commonly, the fragments are ions, e. g.
AgNO3(aq) + NaCl(aq) = AgCl(s) + NaNO3(aq)
electrolyte.  
A substance that dissociates fully or partially into ions when dissolved in a solvent, producing a solution that conducts electricity. See strong electrolyte, weak electrolyte.
endpoint. end point. Compare with equivalence point.
The experimental estimate of the equivalence point in a titration.
equivalence point. Compare with end point.
The equivalence point is the point in a titration when enough titrant has been added to react completely with the analyte.
formation. formation reaction.
A reaction that forms one mole of a compound from its elements in their most stable forms. For example, the formation reaction for water is H2(g) + ½O2  H2O().
indicator.
A substance that undergoes an sharp, easily observable change when conditions in its solutions change. See, for example, acid-base indicator and redox indicator.
insoluble. insolubility. Compare with soluble.
Refers to a substance that does not dissolve in a solvent to any significant degree. Compounds with solubilities of less than 1 g per liter of water are often referred to as 'insoluble', even though they do dissolve to a small extent.
ionic dissociation. ionize; ionization.
When ionic substances dissolve, their ions are surrounded by solvent molecules and separated from each other. This phenomena is also called ionization.
ionic equation. complete ionic equation . Compare with net ionic equation and molecular equation.
An ionic equation is a balanced chemical equation in which strong electrolytes are written as dissociated ions. For example, Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) = AgCl(s) + Na+(aq) + NO3-(aq) is an ionic equation; AgNO3(aq) + NaCl(aq) = AgCl(s) + NaNO3(aq) is not.
limiting reactant. limiting reagent.
The reactant that limits the amount of product produced in a chemical reaction. For example, mixing one mole of H2(g) with one mole of O2 produces one mole of steam (H2O(g)), with half a mole of O2(g) remaining. The hydrogen gas limits the amount of steam produced in this case.
molecular equation. Compare with ionic equation
A molecular equation is a balanced chemical equation in which ionic compounds are written as neutral formulas rather than as ions. For example, AgNO3(aq) + NaCl(aq) = AgCl(s) +NaNO3(aq) is a molecular equation; Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) = AgCl(s) + Na+(aq) + NO3-(aq) is not.
net ionic equation. Compare with net ionic equation and molecular equation.
A net ionic equation is an ionic equation with all DEFINE[spectator ions">spectator ions eliminated. For example, Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) = AgCl(s) + Na+(aq) + NO3-(aq) is an ionic equation; the net ionic equation would be Ag+(aq) + Cl-(aq) = AgCl(s) because the sodium and nitrate ions are spectators (they appear on both sides of the ionic equation.
neutral.
1. having no net electrical charge. Atoms are electrically neutral; ions are not. 2. A solution containing equal concentrations of H+ and OH-.
neutralization reaction. neutralization; acid-base reaction.
A chemical change in which one compound aquires H+ from another. The compound that receives the hydrogen ion is the base; the compound that surrenders it is an acid.
nonelectrolyte.
A nonelectrolyte is a substance which does not ionize in solution.
percent yield. percentage yield. Compare with theoretical yield and actual yield.
Percent yield equals experimental yield divided by theoretical yield times 100%.
polar molecule. polar. Compare with covalent compound, ionic compound and polar bond.
An asymmetric molecule containing polar bonds. H2O, NH3, and HCl are examples of polar molecules. Non-examples are CO2, CCl4, and BCl3 which contain polar bonds but are nonpolar because they have symmetric shapes. Alkanes are usually asymmetric but are nonpolar because they contain no polar bonds. Polar molecules are electric dipoles and they attract each other via dipole-dipole forces.
precipitate. () ppt.
An insoluble substance that has been formed from substances dissolved in a solution. For example, mixing silver nitrate and sodium chloride solutions produces a precipitate, insoluble silver chloride (along with soluble sodium nitrate.
precipitation.
Precipitation is the conversion of a dissolved substance into insoluble form by chemical or physical means.
product. Compare with reactant.
A substance that is produced during a chemical change.
reactant. Compare with product.
A substance that is consumed during a chemical change.
rearrangement reaction. isomerization; isomerize.
A reaction in which a reactant and product are isomers of each other. Chemical bonds within the reactant are broken and reformed to produce the product.
redox reaction. electrochemical reaction; oxidation-reduction reaction; redox.
A reaction that involves transfer of electrons from one substance to another. Redox reactions always involve a change in oxidation number for at least two elements in the reactants.
saturated solution. Compare with supersaturated solution.
A solution which does not dissolve any more solute. When a saturated solution is placed in contact with additional solute, solute neither dissolves nor is deposited from a saturated solution.
solubility. solubilities; equilibrium solubility; solubleness.
The solubility of a substance is its concentration in a saturated solution. Substances with solubilities much less than 1 g/100 mL of solvent are usually considered insoluble. The solubility is sometimes called "equilibrium solubility" because the rates at which solute dissolves and is deposited out of solution are equal at this concentration.
spectator ion.
A spectator ion is an ion that appears as both a reactant and a product in an ionic equation. For example, in the ionic equation
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) = AgCl(s) + Na+(aq) + NO3-(aq)
the sodium and nitrate ions are spectator ions.
standard solution.
A solution of precisely known concentration.
stoichiometry.
1. Ratios of atoms in a compound. 2. Ratios of moles of compounds in a reaction. 3. A branch of chemistry that quantitatively relates amounts of elements and compounds involved in chemical reactions, based on the law of conservation of mass and the law of definite proportions.
strong acid. Compare with weak acid.
A strong acid is an acid that completely dissociates into hydrogen ions and anions in solution. Strong acids are strong electrolytes. There are only six common strong acids: HCl (hydrochloric acid), HBr (hydrobromic acid), HI (hydroiodic acid), H2SO4 (sulfuric acid), HClO4 (perchloric acid), and HNO3 (nitric acid).
strong base.
A strong base is an base that completely dissociates into ions in solution. Strong bases are strong electrolytes. The most common strong bases are alkali metal and alkaline earth metal hydroxides.
strong electrolyte. Compare with weak electrolyte.
A strong electrolyte is a solute that completely dissociates into ions in solution. Solutions of strong electrolytes conduct electricity. Most soluble ionic compounds are strong electrolytes.
supersaturated solution. supersaturated.
A supersaturated solution has concentration of solute that is higher than its solubility. A crystal of solute dropped into a supersaturated solution grows; excess solute is deposited out of the solution until the concentration falls to the equilibrium solubility.
Synthesis. synthesize; synthetic reaction. Compare with decomposition.
Formation of a complex product from simpler reactants. For example, water can be synthesized from oxygen and hydrogen gas: H2(g) + ½O2(g)  H2O().
theoretical yield. maximum yield; stoichiometric yield. Compare with actual yield and percent yield.
The amount of product obtained when all of the limiting reagent reacts.
titrant.
The substance that quantitatively reacts with the analyte in a titration. The titrant is usually a standard solution added carefully to the analyte until the reaction is complete. The amount of analyte is calculated from the volume of titrant required for complete reaction.
titration curve.
A plot that summarizes data collected in a titration. A linear titration curve plots moles of analyte (or, some quantity proportional to moles of analyte) on the Y axis, and the volume of titrant added on the X axis. Nonlinear plots use the log of the concentration of the analyte instead. Nonlinear titration curves are often used for neutralization titrations (pH vs. mL NaOH solution). Logs are used to exaggerate the rate of change of concentration on the plot, so that the endpoint can be determined from the point of maximal slope.
titration.
A procedure for determining the amount of some unknown substance (the analyte) by quantitative reaction with a measured volume of a solution of precisely known concentration (the titrant).
weak acid. Compare with strong acid.
An acid that only partially dissociates into hydrogen ions and anions in solution. Weak acids are weak electrolytes. Recognize weak acids by learning the six common strong acids; any acid that doesn't appear on the list of strong acids is usually a weak acid.
weak base. Compare with strong base.
A base that only partially dissociates into ions in solution. Weak bases are weak electrolytes. Ammonia is an example of a weak base; the reaction NH3(aq) + H2O(l) = NH4_+(aq) + OH-(aq) is reversible.
weak electrolyte. Compare with strong electrolyte.
A weak electrolyte is a solute that incompletely dissociates into ions in solution. For example, acetic acid partially dissociates into acetate ions and hydrogen ions, so that an acetic acid solution contains both molecules and ions. A solution of a weak electrolyte can conduct electricity, but usually not as well as a strong electrolyte because there are fewer ions to carry the charge from one electrode to the other.
yield. experimental yield; actual yield. Compare with theoretical yield and percent yield.
The amount of product actually obtained in a chemical reaction.

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acetate.  (CH3COO-, C2H3O2-) acetate ion.
1. an ion formed by removing the acidic hydrogen of acetic acid, HC2H3O2. 2. a compound derived by replacing the acidic hydrogen in acetic acid. 3. A fiber made of cellulose acetate.

acetic acid  (CH3COOH, HC2H3O2) ethanoic acid; vinegar acid; methanecarboxylic acid.
A simple organic acid that gives vinegar its characteristic odor and flavor. Glacial acetic acid is pure acetic acid.

acid. ([Lat. acidus, sour]) Compare with base.
1. a compound which releases hydrogen ions (H+) in solution (Arrhenius). 2. a compound containing detachable hydrogen ions (Bronsted-Lowry). 3. a compound that can accept a pair of electrons from a base (Lewis)..

addition compound. complex compound. Compare with hydrate.
An addition compound contains two or more simpler compounds that can be packed in a definite ratio into a crystal. A dot is used to separate the compounds in the formula. For example, ZnSO4·7 H2O is an addition compound of zinc sulfate and water. This represents a compound, and not a mixture, because there is a definite 1:7 ratio of zinc sulfate to water in the compound. Hydrates are a common type of addition compound.

alkaline earth. 
An oxide of an alkaline earth metal, which produces an alkaline solution in reaction with water.

alkane. paraffin. Compare with hydrocarbon and alkene.
A series of organic compounds with general formula CnH2n+2. Alkane names end with -ane. Examples are propane (with n=3) and octane (with n=8).

ammonia.  (NH3) Compare with ammonium
Pure NH3 is a colorless gas with a sharp, characteristic odor. It is easily liquified by pressure, and is very soluble in water. Ammonia acts as a weak base. Aqueous solutions of ammonia are (incorrectly) referred to as "ammonium hydroxide".

ammonium ion.  (NH4+) ammonium.
NH4+ is a cation formed by neutralization of ammonia, which acts as a weak base.

anhydrous. anhydrous compound; anhydride. Compare with hydrate.
A compound with all water removed, especially water of hydration. For example, strongly heating copper(II) sulfate pentahydrate (CuSO4·5H2O) produces anhydrous copper(II) sulfate (CuSO4).

anion.  Compare with cation.
An anion is a negatively charged ion. Nonmetals typically form anions.

base. alkali; alkaline; basic. Compare with acid.
1. a compound that reacts with an acid to form a salt. 2. a compound that produces hydroxide ions in aqueous solution (Arrhenius). 3. a molecule or ion that captures hydrogen ions.(Bronsted-Lowry). 4. a molecule or ion that donates an electron pair to form a chemical bond.(Lewis).

binary compound.  Compare with compound.
A compound that contains two different elements. NaCl is a binary compound; NaClO is not.

Brösted acid. Compare with acid.
A material that gives up hydrogen ions in a chemical reaction.

Brösted base. Compare with base.
A material that accepts hydrogen ions in a chemical reaction.

cation.  Compare with anion.
A cation is a positively charged ion. Metals typically form cations.

chemical bond. bond; bonding; chemical bonding.
A chemical bond is a strong attraction between two or more atoms. Bonds hold atoms in molecules and crystals together. There are many types of chemical bonds, but all involve electrons which are either shared or transferred between the bonded atoms.

covalent bond. covalent; covalently bound. Compare with covalent compound and ionic bond.
A covalent bond is a very strong attraction between two or more atoms that are sharing their electrons. In structural formulas, covalent bonds are represented by a line drawn between the symbols of the bonded atoms.

covalent compound. molecular compound. Compare with ionic bond and ionic compound.
A compound made of molecules- not ions. The atoms in the compound are bound together by shared electrons. Also called a molecular compound.

cupric.  (Cu2+) cupric ion.
Deprecated. 1. the copper(II) ion, Cu2+. 2. A compound that contains copper in the +2 oxidation state.

cuprous.  (Cu+) cuprous ion.
Deprecated. 1. the copper(I) ion, Cu+. 2. A compound that contains copper in the +1 oxidation state.

diatomic molecule.  Compare with binary compound and polyatomic molecule
A molecule that contains only two atoms. All of the noninert gases occur as diatomic molecules; e. g. hydrogen, oxygen, nitrogen, fluorine, and chlorine are H2, O2, N2, F2, and Cl2, respectively.

efflorescent. efflorescence; efflorescing. Compare with deliquescent and hygroscopic.
Efflorescent substances lose water of crystallization to the air. The loss of water changes the crystal structure, often producing a powdery crust.

element Compare with compound and mixture.
An element is a substance composed of atoms with identical atomic number. The older definition of element (an element is a pure substance that can't be decomposed chemically) was made obsolete by the discovery of isotope.

empirical formula. simplest formula. Compare with molecular formula.
Empirical formulas show which elements are present in a compound, with their mole ratios indicated as subscripts. For example, the empirical formula of glucose is CH2O, which means that for every mole of carbon in the compound, there are 2 moles of hydrogen and one mole of oxygen.

ferric. ferric ion.
Deprecated. 1. the iron(III) ion, Fe3+. 2. A compound that contains iron in the +3 oxidation state.

ferrous. ferrous ion.
Deprecated. 1. the iron(II) ion, Fe2+. 2. A compound that contains iron in the +2 oxidation state.

formula weight. formula mass. Compare with molecular weight and empirical formula.
The formula weight is the sum of the atomic weights of the atoms in an empirical formula. Formula weights are usually written in atomic mass units (u).

formula unit. Compare with empirical formula.
One formula weight of a compound.

halide. halide ion.
A compound or ion containing fluorine, chlorine, bromine, iodine, or astatine.

hydrate. Compare with addition compound.
A hydrate is an addition compound that contains water in weak chemical combination with another compound. For example, crystals of CuSO4·5 H2O (copper sulfate pentahydrate) are made of regularly repeating units, each containing 5 molecules of water weakly bound to a copper(II) ion and a sulfate ion.

hydrazine. (NH2NH2)
A colorless, fuming, corrosive liquid that is a powerful reducing agent. NH2NH2 is used in jet and rocket fuels, and as an intermediate in the manufacture of agricultural, textile, photographic, and industrial chemicals.

hydrocarbon. Compare with alkane, alkene, alkyne, and organic.
Hydrocarbons are organic compounds that contain only hydrogen and carbon. The simplest hydrocarbons are the alkanes.

hydronium ion. (H3O+) hydronium.
The H3O+ ion, formed by capture of a hydrogen ion by a water molecule. A strong covalent bond is formed between the hydrogen ion and water oxygen; all hydrogen ions in aqueous solution are bound inside hydronium ions.

hydroxide. (OH-) hydroxide ion. Compare with hydroxyl.
1. The OH- ion. 2. Compounds containing the OH- ion. See also: hydroxide compounds.

hygroscopic.
Able to absorb moisture from air. For example, sodium hydroxide pellets are so hygroscopic that they dissolve in the water they absorb from the air.

hygroscopicity.
The ability of a substance to absorb moisture from air. For example, sodium hydroxide pellets are so hygroscopic that they dissolve in the water they absorb from the air.

inorganic compound. inorganic. Compare with organic.
A compound that does not contain carbon chemically bound to hydrogen. Carbonates, bicarbonates, carbides, and carbon oxides are considered inorganic compounds, even though they contain carbon.

ionic bond. ionically bound; ionic bonding. Compare with covalent bond.
An attraction between ions of opposite charge. Potassium bromide consists of potassium ions (K+) ionically bound to bromide ions (Br-). Unlike covalent bonds, ionic bond formation involves transfer of electrons, and ionic bonding is not directional.

ionic compound. salt. Compare with covalent compound and ionic bond.
A compound made of distinguishable cations and anions, held together by electrostatic forces.

IUPAC
International Union of Pure and Applied Chemistry, an organization which sets international standards for chemical nomenclature, atomic weights, and the names of newly discovered elements.

law of conservation of mass.
There is no change in total mass during a chemical change. The demonstration of conservation of mass by Antoine Lavoisier in the late 18th century was a milestone in the development of modern chemistry.

law of definite proportions.
When two pure substances react to form a compound, they do so in a definite proportion by mass. For example, when water is formed from the reaction between hydrogen and oxygen, the 'definite proportion' is 1 g of H for every 8 g of O.

law of multiple proportions.
When one element can combine with another to form more than one compound, the mass ratios of the elements in the compounds are simple whole-number ratios of each other. For example, in CO and in CO2, the oxygen-to-carbon ratios are 16:12 and 32:12, respectively. Note that the second ratio is exactly twice the first, because there are exactly twice as many oxygens in CO2 per carbon as there are in CO.

molecular formula. formula; chemical formula. Compare with empirical formula.
A notation that indicates the type and number of atoms in a molecule. The molecular formula of glucose is C6H12O6, which indicates that a molecule of glucose contains 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen.

molecular model stick model; ball and stick model; spacefilling model.
A representation of a molecule. The model can be purely computational or it can be an actual physical object. Stick models show bonds, ball-and-stick models show bonds and atoms, and spacefilling models show relative atomic sizes.

molecular weight. molecular mass. Compare with formula weight and molecular formula.
The average mass of a molecule, calculated by summing the atomic weights of atoms in the molecular formula. Note that the words mass and weight are often used interchangeably in chemistry.

nomenclature.
A system for naming things. For example, "organic nomenclature" is the system used to name organic compounds

octane. (C8H18) Compare with alkane and hydrocarbon.
Flammable liquid compounds found in petroleum and natural gas. There are 18 different octanes- they have different structural formulas but share the molecular formula C8H18. Octane is used as a fuel and as a raw material for building more complex organic molecules. It is the eighth member of the alkane series.

organic. organic compound. Compare with inorganic compound.
Compounds that contain carbon chemically bound to hydrogen. They often contain other elements (particularly O, N, halogens, or S). Organic compounds were once thought to be produced only by living things. We now know that any organic compound can be synthesized in the laboratory (although this can be extremely difficult in practice!)

polyatomic ion. Compare with molecule, ion and polyatomic molecule.
A polyatomic ion is a charged particle that contains more than two covalently bound atoms. See Polyatomic Ions for more.

polyatomic molecule. Compare with polyatomic ion and diatomic molecule.
A polyatomic molecule is an uncharged particle that contains more than two atoms.

propane. (C3H8) Compare with alkane and hydrocarbon.
A colorless, odorless, flammable gas, found in petroleum and natural gas. It is used as a fuel and as a raw material for building more complex organic molecules. Propane is the third member of the alkane series.

proton donor. acid. Compare with base.
Because a free H+ ion is technically a bare proton, acids are sometimes referred to as "proton donors" because they release hydrogen ions in solution. The term "proton donor" is misleading, since in aqueous solution, the hydrogen ion is never a bare proton- it's covalently bound to a water molecule as an H3O+ ion. Further, acids don't "donate" protons; they yield them to bases with a stronger affinity for them.

stoichiometry.
1. Ratios of atoms in a compound. 2. Ratios of moles of compounds in a reaction. 3. A branch of chemistry that quantitatively relates amounts of elements and compounds involved in chemical reactions, based on the law of conservation of mass and the law of definite proportions.

structural formula. Compare with molecular formula and empirical formula.
A structural formula is a diagram that shows how the atoms in a molecule are bonded together. Atoms are represented by their element symbols and covalent bonds are represented by lines. The symbol for carbon is often not drawn. Most structural formulas don't show the actual shape of the molecule (they're like floor plans that show the layout but not the 3D shape of a house).

sugar.
A carbohydrate with a characteristically sweet taste. Sugars are classified as monosaccharides, disaccharides, or trisaccharides.

superoxide. superoxide ion.
A binary compound containing oxygen in the -½ oxidation state. For example, KO2 is potassium superoxide, an ionic compound containing the superoxide ion, O2-.

thio-.
A prefix that means, "replace an oxygen with sulfur". For example, sulfate ion is SO42-; thiosulfate ion is S2O32-. Cyanate ion is OCN-; thiocyanate ion is SCN-.

water of crystallization. water of hydration.
Water that is stoichiometrically bound in a crystal; for example, the waters in copper sulfate pentahydrate.