Glossary - Bb
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Back titration | Determining the concentration of an analyte by reacting it with a known number of moles of excess reagent. The excess reagent is then titrated with a second reagent. The concentration of the analyte in the original solution is then related to the amount of reagent consumed. | ||||
| Balanced equation | 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). | ||||
| Balmer series | A series of lines in the emission spectrum of hydrogen that involve transitions to the n=2 state from states with n>2. | ||||
| Band | 1. A set of closely spaced energy levels in an atom, molecule, or metal. 2. A set of closely spaced lines in an absorption spectrum or emission spectrum. 3. A range of frequencies or wavelengths. | ||||
| Band spectrum | An emission spectrum that contains groups of sharp peaks that are so close together that they are not distinguishable separately, but only as a "band". | ||||
| bar | Unit of pressure. 1 bar = 105 pascals = 1.01325 atmospheres. | ||||
| Barometer | An instrument that measures atmospheric pressure. A mercury barometer is a closed tube filled with mercury inverted in a mercury reservoir. The height of the mercury column indicates atmospheric pressure (with 1 atm = 760 mm of mercury). An aneroid barometer consists of an evacuated container with a flexible wall. When atmospheric pressure changes, the wall flexes and moves a pointer which indicates the changing pressure on a scale. | ||||
| Base hydrolysis constant | (Kb) base ionization constant; basic hydrolysis constant. Compare with acid dissociation constant. The equilibrium constant for the hydrolysis reaction associated with a base. For example, Kb for ammonia is the equilibrium constant for NH3(aq) + H2O( ) NH4+(aq) + OH-(aq), or Kb = [NH4+][OH-]/[NH3]. | ||||
| Base unit | Base units are units that are fundamental building blocks in a system of measurement. There are seven base units in the SI system. | ||||
| Base | 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). | ||||
| Basis function | A mathematical function that can be used to build a description of wavefunctions for electrons in atoms or molecules. | ||||
| Basis set | A set of mathematical functions that are combined to approximate the wavefunctions for electrons in atoms and molecules. | ||||
| Baumé | (be°Bé, °B) Baumé scale; degrees Baumé; Baume; Baumé scale. A, Be scale related to specific gravities, devised by the French chemist Antoine Baumé for marking hydrometers. At 60°F, specific gravity can be calculated from degrees Baumé by the following formulas:
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| Beer's law | (A=abc or A=  bc) Beer-Lambert law.In absorption spectroscopy, the absorbance of a dilute solution is equal to its absorptivity times the path length times the concentration of the absorbing solute. | ||||
| Beryllium | (Be) Be; glucinium. Element 4, atomic weight 9.0122, an extremely toxic metal used as a neutron source and in phosphors. | ||||
| Beta particle | (ß-) An electron emitted by an unstable nucleus, when a neutron decays into a proton and an electron. In some cases, beta radiation consists of positrons ("antielectrons" which are identical to electrons but carry a +1 charge.") Note that beta particles are created in nuclear decay; they do not exist as independent particles within the nucleus. | ||||
| Bidentate | A ligand that has two "teeth" or atoms that coordinate directly to the central atom in a complex. For example, 1,10-phenanthroline is a bidentate ligand of iron. | ||||
| Binary compound | A compound that contains two different elements. NaCl is a binary compound; NaClO is not. | ||||
| Biochemistry | The chemistry of living things, including the structure and function of biological molecules and the mechanism and products of their reactions. | ||||
| Bleach | A dilute solution of sodium hypochlorite or calcium hypochlorite which kills bacteria and destroys colour organic materials by oxidizing them. | ||||
| Block | A region of the periodic table that corresponds to the type of subshell (s, p, d, or f) being filled during the Aufbau construction of electron configurations. | ||||
| Bohr atom | Bohr's theory; Bohr's atomic theory; Bohr model. A model of the atom that explains emission and absorption of radiation as transitions between stationary electronic states in which the electron orbits the nucleus at a definite distance. The Bohr model violates the Heisenberg uncertainty principle, since it postulates definite paths and momenta for electrons as they move around the nucleus. Modern theories usually use atomic orbitals to describe the behaviour of electrons in atoms. | ||||
| Bohr radius | (a0) bohr. The atomic unit of length, equal to 0.529 177 2083 × 10-10 m, with an uncertainty of 0.000 000 0019 × 10-10 m [1998 CODATA values]. | ||||
| Boiling point | The temperature at which the vapour pressure of a liquid is equal to the external pressure on the liquid. The standard boiling point is the temperature at which the vapour pressure of a liquid equals standard pressure. | ||||
| Boiling point elevation | The boiling point of a solution is higher than the boiling point of the pure solvent. Boiling point elevation is a colligative property. | ||||
| Boltzmann constant | (k) A fundamental constant equal to the ideal gas law constant divided by Avogadro's number, equal to 1.3805 × 10-23 J K-1. | ||||
| Boltzmann equation | A statistical definition of entropy, given by S = k ln W, where S and k are the entropy and Boltzmann's constant, respectively, and W is the probability of finding the system in a particular state. | ||||
| Bond energy | Energy change per mole when a bond is broken in the gas phase for a particular substance. | ||||
| Bond enthalpy | Enthalpy change per mole when a bond is broken in the gas phase for a particular substance. | ||||
| Bond length | The average distance between the nuclei of two bonded atoms in a stable molecule. | ||||
| Bond order | 1. In Lewis structures, the number of electron pairs shared by two atoms. 2. In molecular orbital theory, the net number of electron pairs in bonding orbitals (calculated as half the difference between the number of electrons in bonding orbitals and the number of electrons in antibonding orbitals. | ||||
| Bond strength | Some measure of how difficult it is to break a chemical bond, for example, a bond energy or a bond enthalpy. | ||||
| Boron | (B) B. Element 5, atomic weight 10.811. Hard yellow crystals or brown amorphous powder, used as a neutron absorber in nuclear chemistry and as a hardener in alloys. | ||||
| Boyle's law | The pressure of a ideal gas is inversely proportional to its volume, if the temperature and amount of gas is held constant. Doubling gas pressure halves gas volume, if temperature and amount of gas don't change. If the initial pressure and volume are P1 and V1 and the final pressure and volume are P2V2, then P1V1 = P2V2 at fixed temperature and gas amount. | ||||
| Brass | A shiny yellow to yellow-orange alloy that contains about two parts copper for every one part zinc. | ||||
| Bronze | A yellow to yellow-brown alloy that contains mostly copper and tin, with small amounts of other metals. | ||||
| Brösted acid | A material that gives up hydrogen ions in a chemical reaction. | ||||
| Brösted base | A material that accepts hydrogen ions in a chemical reaction. | ||||
| Brownian motion | Small particles suspended in liquid move spontaneously in a random fashion. The motion is caused by unbalanced impacts of molecules on the particle. Brownian motion provided strong circumstantial evidence for the existence of molecules. | ||||
| Buckminsterfullerene | (C60) C60; fullerene; buckyball. A form of carbon consisting of 60 carbon atoms bound together to make a roughly spherical "buckyball" (which looks rather like a soccer ball). | ||||
| Buffer | pH buffer; buffer solution. A solution that can maintain its pH value with little change when acids or bases are added to it. Buffer solutions are usually prepared as mixtures of a weak acid with its own salt or mixtures of salts of weak acids. For example, a 50:50 mixture of 1 M acetic acid and 1 M sodium acetate buffers pH around 4.7. | ||||
| Bunsen burner | A gas burner with adjustable air intake, commonly used in laboratories. | ||||
| Buret | A cylindrical glass tube closed by a stopcock on one end and open on the other, with volume gradations marked on the barrel of the tube, used to precisely dispense a measured amount of a liquid. | ||||
| Butanol | An alcohol containing four carbon atoms. Example: 1-butanol. |
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