Chemistry Definitions Starting With the Letter B   Recently updated !

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This chemistry dictionary offers the chemistry definitions starting with the letter B. These glossary terms are commonly used in chemistry and chemical engineering. Click the letter below to find the terms and definitions beginning with that letter.


β-branching – Beta branching is when a substituent is attached at a beta carbon. Beta branching is denoted as β-branching.

β-carbon – The beta carbon is the carbon atom one bond removed from the α-carbon in a molecule away from the moiety of interest. β-carbon is the most common notation of the beta carbon.

β-hydrogen – A beta hydrogen is a hydrogen atom bonded to the β-carbon of a molecule. β-hydrogen is the most common notation for beta hydrogen.

β-hydroxy acid – A beta-hydroxy acid is an acid containing a hydroxyl group attached to a β-carbon after the carboxyl group. Beta-hydroxy acid is also written as β-hydroxy acid or BHA.

background noise – Background noise is the sum of all noise or interference in a measurement which is independent of the data signal.
Also known as: noise, interference

background radiation – Background radiation refers to the radiation originating from sources other than the sources being observed. Most background radiation comes from two sources, cosmic radiation, and radioisotopes in the rocks and soil. The amounts vary with the geology of the area (different rocks are made up of different elements) and elevation (less atmosphere at higher elevations to absorb cosmic radiation).

back titration – Back titration is a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent. The remaining excess reagent is then titrated with another second reagent. The second titration’s results show how much of the excess reagent was used in the first titration and the original analyte’s concentration can then be calculated.

bactericide – A bactericide is a substance that kills bacteria.
Also known as: bacteriocide

Baeyer reagent – Baeyer reagent is dilute cold potassium permanganate solution, used to oxidize alkenes and alkynes.

bainite – Bainite is a Fe-C composition which consists of a fine dispersion of cementite in alpha-ferrite. Bainite is an austenitic transformation product that forms at temperatures between those at which the pearlite and martensite transformations occur.

balanced equation – An equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge is the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction.
Also known as: Balancing the equation, balancing the reaction, conservation of charge and mass.

Balmer series – The Balmer series is the portion of the emission spectrum of hydrogen that represents electron transitions from energy levels n > 2 to n = 2. These are four lines in the visible spectrum.
Examples: The four visible Balmer lines of hydrogen appear at 410 nm, 434 nm, 486 nm and 656 nm.

band gap energy – The band gap energy is the span of energies that lie between the valence and conduction bands for insulators and semiconductors.

bar – A bar is a unit of pressure that is defined to be equal to 105 pascals. 1 bar = 105 Pascals = 1.01325 atmospheres = 14.5038 psi (pounds per square inch) = 29.53 in Hg (inches of mercury).

barium – Barium is the name for the alkaline earth element with atomic number 56 and is represented by the symbol Ba.

barometer – A barometer is a device that measures atmospheric pressure.

barrel – A barrel is a unit of volume. The volume of a barrel varies according to the industry.
For the petroleum industry: 1 barrel = 42 US gallons = 159 liters
Beer industry: 1 barrel = 31 US gallons = 117 liters
Dry goods: 1 barrel = 7,056 cubic inches = 115.6 liters.

base – A base is an aqueous solution having a pH greater than 7 or having a [OH] greater than 10-7.
Also known as: alkaline

base anhydride – A basic anhydride or base anhydride is a metal oxide that forms a basic solution when reacted with water.
Example: An example of a base anhydride is CaO, which turns into CaOH in water.

base catalysis – Base catalysis is a chemical reaction that requires the presence of a base to act as a catalyst to proceed.

base dissociation constant (Kb) – The base dissociation constant is the equilibrium constant that measures the extent of dissociation for a base.
Example: The Base Dissociation Constant (Kb) for a base BOH is denoted by:
Kb = [B+]·[OH] / [BOH]

base promoted – Base promoted refers to a chemical reaction that needs a base to proceed but does not act as a catalyst for the reaction. Reactions needing a base and act as catalysts are called base catalysis reactions.

base metal – A base metal is any metal not considered precious.
Examples: Aluminum, zinc, copper, and lead are considered base metals.

basic – Basic refers to an aqueous solution having a pH greater than 7 or having a [OH] greater than 10-7.

basic anhydride – Basic anhydride is another term for base anhydride. See definition above.

basic solution – Basic solution is another term for basic. See definition above.

batch reactor – A batch reactor is a reactor which is characterized by its operation. In the case of a batch reactor, this means the reactor reaches steady state.

battery – A battery is a series of electrochemical cells using redox reactions to provide a source of electric current.

battery acid – Battery acid is any acid that can be used in a chemical cell or battery. The common use of the term battery acid refers to the acids used in lead-acid batteries for motor vehicles. Automotive battery acid is 30-50% sulfuric acid (H2SO4) with water. The acid typically has a mole fraction of 29-32%, concentration of 4.2-5.0 mol/L, a density of 1.25-1.28 kg/L and a pH of approximately 0.8.

BCC – Body centered cubic or BCC refers to a crystal structure in which atoms are located at the corners of a cubic cell with one atom at the cell center position.

becquerel – The becquerel is an SI unit of radioactive activity. 1 becquerel = 1 radioactive decay/second (occasionally called 1 disintegration/second).

Beer-Lambert law – Beer’s Law is an equation that relates the attenuation of light to properties of a material. The law states the concentration of a chemical is directly proportional to the absorbance of a solution. Beer’s Law is written as:
A = εbc
where A is absorbance (no units)
ε is the molar absorbtivity with units of L mol-1 cm-1 (formerly called the extinction coefficient)
b is the path length of the sample, usually expressed in cm
c is the concentration of the compound in solution, expressed in mol L-1
The Beer-Lambert law does not hold at high concentration.

Beer’s law – Beer’s law is a short name for the Beer-Lambert law. See definition above.

benzenoid ring – A benzenoid ring is an aromatic ring that possesses a benzene-like structure.

benzyl group – The benzyl group is the C6H5-CH2– substituent. Benzyl group is a benzene ring bonded to a CH2 group.

benzyne – In organic chemistry: an unstable intermediate species consisting of a benzene ring with an adjacent chemical bond created by the side-to-side overlap of the sp2 orbitals on the adjacent carbon atoms of the ring.

berkelium – Berkelium is the name for the actinide element with atomic number 97 and is represented by the symbol Bk.

berylliumBeryllium is the name for the alkaline earth element with atomic number 4 and is represented by the symbol Be.

beta branching – Beta branching is when a substituent is attached at a beta carbon. Beta branching is also denoted as β-branching.

beta carbon – The beta carbon is the carbon atom one bond removed from the α-carbon in a molecule away from the moiety of interest. β-carbon is the most common notation of the beta carbon.

beta decay – Beta decay refers to the spontaneous radioactive decay where a beta particle is produced. There are two types of beta decay where the beta particle is either an electron or a positron.
β decay occurs when an electron is the beta particle. An atom will β decay when a neutron in the nucleus converts to a proton by the reaction
ZXAZYA+1 + e + antineutrino
where X is the parent atom, Y is the daughter atom, Z is the atomic mass of X, A is the atomic number of X.
β+ decay occurs when a positron is the beta particle. An atom will β+ decay when a proton in the nucleus converts into a neutron by the reaction
ZXAZYA-1 + e+ + neutrino
where X is the parent atom, Y is the daughter atom, Z is the atomic mass of X, A is the atomic number of X.
In both cases, the atomic mass of the atom remains constant but the elements are transmuted by one atomic number.
Examples: Cesium-137 decays to Barium-137 by β decay. Sodium-22 decays to Neon-22 by β+ decay.

beta hydrogen – A beta hydrogen is a hydrogen atom bonded to the β-carbon of a molecule. β-hydrogen is the most common notation for beta hydrogen.

beta-hydroxy acid – A beta-hydroxy acid is an acid containing a hydroxyl group attached to a β-carbon after the carboxyl group.

beta particle – A beta particle is either an electron or a positron. The term is generally applied to an electron or positron emitted in radioactive beta decay.

beta radiation – Beta radiation is the ionizing radiation resulting from the process of beta decay.

bidentate – Bidentate refers to a coordination complex where two ligands can attach itself to a central atom.
Also known as: didentate
Example: Ethylenediamine is a bidentate ligand. The ligand can attach to a central atom at either of the unpaired electrons on the nitrogen atoms.

bidentate ligand – A bidentate ligand is an atom, ion, or molecule that can attach twice to a metal ion.

bifunctional monomer – A bifunctional monomer is a monomer unit with two active bonding positions.

bimolecular – Bimolecular refers to an elementary chemical reaction that occurs when two reactant molecules collide with each other.

binary acid – A binary acid is a binary compound where one element is hydrogen and the other is a nonmetal.
Examples: Hydrochloric – HCl, hydrofluoric – HF and hydroiodic – HI are all binary acids.

binary compound – A binary compound is a compound made up of two elements.
Example: Water (H2O) is a binary compound. It contains the two elements hydrogen and oxygen.

binding energy – Binding energy is the energy required to either separate an electron from an atom or to separate the protons and neutrons of an atomic nucleus.

biochemistry – Biochemistry is the chemistry of living things. It is concerned with the structure and chemical processes of proteins, carbohydrates, lipids, nucleic acids and other molecules found in or produced by organisms.

biocide – A biocide is a substance or microorganism that kills or controls the growth of living organisms.
Examples: Antibiotics, pesticides, and antibacterials are all types of biocides.

biology – Biology is the scientific study of life. Biology involves the study of living organisms and how they relate to their environment. Fields of biology include botany, zoology, microbiology, biochemistry, genetics, molecular biology, cellular biology, physiology, and ecology.

bioorganic chemistry – Bioorganic chemistry is a chemistry discipline which integrates biochemistry and organic chemistry. Bioorganic chemistry involves the study of biological processes using chemical methods. Organic chemistry methods are used to synthesize biological molecules and to examine their structure and the kinetics of biochemical reactions.

bismuth – Bismuth is the name for the metal element with atomic number 83 and is represented by the symbol Bi.

bitumen – Bitumen is a naturally occurring mixture of polycyclic aromatic hydrocarbons. The mixture takes the form of a viscous, black, sticky tar-like substance. It can be refined from crude oil by fractional distillation.
Examples: Asphalt is a mixture of an aggregate and bitumen and is commonly used as a road surface. Bitumen is also what makes up the La Brea Tar Pits.

black body – A black body is an idealized material that absorbs all incident electromagnetic radiation. Black bodies emit electromagnetic radiation determined by the temperature of the material regardless of shape or size according to Planck’s law. Antonym: white body
Alternate Spelling: blackbody

black body radiation – Black body radiation refers to the electromagnetic radiation given off by a black body at thermal equilibrium. As the temperature increases, the peak intensity increases and the peak wavelength decreases.

black lead – Black lead is an alternate name for the graphite allotrope of carbon.
Also known as: graphite, blacklead
Example: Black lead is the substance found in most pencils.

black light – A black light is a lamp that emits electromagnetic radiation primarily in the soft near ultraviolet range. A black light emits very little visible light, hence its name.

block – In chemistry, block refers to the regions of the periodic table that corresponds to the outermost subshell of electron orbitals. Blocks are marked by the same letters as electron orbitals: s, p, d, and f. Blocks can be further defined by the energy levels of the outermost orbital.
Examples: The transition metals are all d block elements. Gold is a 5d block element. Carbon is a 2p block element.

block copolymer – A block copolymer is a copolymer formed when the two monomers cluster together and form ‘blocks’ of repeating units. For example, a polymer made up of X and Y monomers joined together like:
is a block copolymer where -Y-Y-Y-Y-Y- and -X-X-X-X-X- groups are the blocks.
Example: The material used to make automobile tires is a block copolymer called SBS rubber. The blocks in SBS rubber are polystyrene and polybutadiene (Styrene-Butadiene-Styrene).

blue vitriol – Blue vitriol is an outdated name for copper sulfate (CuSO4).
Also known as: copper sulfate

body centered cubic – Body centered cubic or BCC refers to a crystal structure in which atoms are located at the corners of a cubic cell with one atom at the cell center position.

bohrium – Bohrium is the name for the transition metal element with atomic number 107 and is represented by the symbol Bh.

Bohr radius – The Bohr radius is the most probable distance between the proton and electron in a hydrogen atom in its ground state. This physical constant is denoted by the symbol a0 and is equal to 5.2917721092(17) x 10-11 m. In most cases, a0 is rounded to 0.529 Å.

boiling – Boiling is the name for the phase transition from the liquid phase to the gas phase.
Also known as: ebullition

boiling point – The boiling point is the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid. Therefore, the boiling point of a liquid depends on atmospheric pressure. The boiling point becomes lower as the external pressure is reduced.

boiling point elevation – Boiling point elevation the phenomenon that occurs when the boiling point of a solvent is increased when another compound is added, such that the resulting solution has a higher boiling point than the pure solvent. Boiling point elevation occurs whenever a non-volatile solute is added to a pure solvent.
Example: The boiling point of salted water is higher than the boiling point of pure water.

Boltzmann’s constant – Boltzmann′s constant is the proportionality constant between the kinetic energy and temperature of molecules of an ideal gas.
Boltzmann′s constant (k or kB) is equal to the ideal gas constant (R) divided by Avogadro’s number (NA).
k = R/NA = 1.3806504(24)x10-23 J⋅K-1

bond – A bond in chemistry is an electrostatic link between atoms in molecules and between ions and molecules in crystals.

bond angle – Bond angle is the angle that is formed between two adjacent bonds on the same atom.
Example: The bond angle between the hydrogen bonds in water is 104.5°.

bond-dissociation energy – Bond-dissociation energy is the amount of energy which is required to homolytically fracture a chemical bond.

bond energy – Bond energy is the amount of energy required to break apart a mole of molecules into its component atoms.

bond enthalpy – Bond enthalpy is the enthalpy change when one mole of bonds is broken in a substance at 298 K. Bond enthalpy refers to the enthalpy change of one particular bond in a molecule.

bond length – Bond length is the equilibrium distance between the nuclei of two groups or atoms that are bonded to each other.

bonding molecular orbital – Bonding molecular orbital refers to the orbital which is formed by the overlap of adjacent atomic orbitals.

bond order – Bond order is a measurement of the number of electrons involved in bonds between two atoms in a molecule. Most of the time, bond order is equal to the number of bonds between two atoms. Exceptions occur when the molecule contains antibonding orbitals. Bond order is calculated by the equation:
Bond order = (number of bonding electrons – number of antibonding electrons)/2
If bond order = 0, the two atoms are not bonded.
Example: The bond order between the two carbons in acetylene ( H-C≡C-H ) is equal to 3. The bond order between the carbon and hydrogen atoms is equal to 1.

boronBoron is the name for the metalloid element with atomic number 5 and is represented by the symbol B.

Boyle’s law – Boyle’s Law is an ideal gas law where at a constant temperature, the volume of an ideal gas is inversely proportional to its absolute pressure. Boyle’s law is often expressed by the formula
PiVi = PfVf
Pi = initial pressure
Vi = initial volume
Pf = final pressure
Vf = final volume

branched chain alkane – A branched chain alkane is an alkane which has alkyl groups bonded to its central carbon chain.

branched polymer – A branched polymer is a polymer containing secondary polymer chains branching off the main chain.

brass – Brass is defined as an alloy of copper and zinc.

bremsstrahlung – Bremsstrahlung is a type of electromagnetic radiation produced when a high energy charged particle is decelerated or deflected by another charged particle.

brimstone – Brimstone is an old name for the element sulfur.

British thermal unit – British thermal unit is a unit of energy equal to the amount of heat required to raise one pound of water 1 degree Fahrenheit at a pressure of 1 atmosphere.
1 BTU ≈ 1.054 Joules ≈ 252 calories

bromination – Bromination is a chemical reaction where a bromine atom is integrated into a molecule.

bromineBromine is the name for the halogen element with atomic number 35 and is represented by the symbol Br.

Bronsted-Lowry acid – A Bronsted-Lowry acid is a material that gives up hydrogen ions during a chemical reaction.
Also known as: Bronsted acid

Bronsted-Lowry base – A Bronsted-Lowry base is a material that accepts hydrogen ions during a chemical reaction.
Also known as: Bronsted base

bronze – Bronze is an alloy of copper, usually containing tin as its main addition.

BTU – BTU is the abbreviation for the British Thermal Unit. See definition above.

buckminsterfullerene – A buckminsterfullerene is carbon allotrope made up of sixty atoms arranged in a sphere. The chemical formula of a buckminsterfullerene is C60. Buckminsterfullerenes are also known as ‘buckyballs’.

buffer – A buffer is a solution containing either a weak acid and its salt or a weak base and its salt, which is resistant to changes in pH.

butter – Butter is a deprecated chemical term for inorganic chlorides.
Examples: Butter of tin is SnCl4. Butter of zinc is ZnCl2.

butter of antimony – Butter of antimony is a deprecated chemistry term for the compound antimony trichloride or SbCl3.

butter of arsenic – Butter of arsenic is a deprecated chemistry term for the compound arsenic trichloride or AsCl3.

butter of bismuth – Old name for bismuth trichloride or BiCl3.

butter of tin – Old chemistry term for the compound tin(IV) chloride or SnCl4.
Also known as: tin tetrachloride

butter of zinc – Old chemistry term for the compound zinc chloride or ZnCl.


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