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Home :Glossary

Glossary: T

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Glossary
T-shape.
A molecular shape that results when there are 3 bonds and 2 lone pairs* around the central atom in the molecule. The atoms bonded to the central atom lie at the ends of a "T" with 90° angles between them. ICl3 has a T-shaped molecular geometry.

tautomer.
A structure formed by facile motion of a hydrogen from one site to another within the same molecule.

temperature. Compare with heat* and thermodynamic temperature*.
Temperature is an intensive property* associated with the hotness or coldness of an object. It determines the direction of spontaneous heat flow (always from hot to cold).

temporary hardness. temporary water hardness. Compare with permanent hardness* and water hardness*.
The component of total water hardness* that can be removed by boiling the water. Ca(HCO3)2 and Mg(HCO3)2_ are responsible for temporary hardness.

teratogen.
A substance that can cause deformities in embryos. Dioxin is a teratogen.

terminal.
1. The end of a polymer* molecule. 2. A point at which electrical connections can easily be made or broken.

terminal reaction.
A reaction that ends a cycle or chain of other chemical reactions.

terminus.
The end of a polymer* molecule.

tetrahedral.
A molecular shape that results when there are four bonds and no lone pairs* around the central atom in the molecule. The atoms bonded to the central atom lie at the corners of a tetrahedron with 109.5° angles between them. The ammonium ion (NH4+) has a tetrahedral molecular geometry.

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.

theory. theories. Compare with hypothesis*.
Theories are well-established explanations for experimental data. To become established, the theory must experimentally tested by many different investigators. Theories usually can not be proven; a single contrary experiment can disprove a theory.

thermal.
Pertaining to heat*.

thermal energy.
energy* an object possesses by virtue of its temperature. For example, 1 g of water at 15°C has 4.184 J more energy than 1 g of water at 14°C.

thermionic emission.
The emission of electrons or ions by a hot object. For example, the filament in a mass spectrometer* spits out energetic electrons that ionize atoms and molecules in the sample.

thermistor.
A device that senses temperature changes by using a resistor with an electrical resistance* that falls when temperature rises.

thermochemical equation.
An compact equation representing a chemical reaction that describes both the stoichiometry* and the energetics of the reaction. For example, the thermochemical equation CH4(g) + 2 O2(g) rightarrow CO2(g) + 2 H2O(g), DeltaH = -2220 kJ means "When one mole of gaseous CH4 is burned in two moles of oxygen gas, one mole of CO2 gas and 2 moles of steam are produced, and 2220 kilojoules of heat are released."

thermochemistry.
The study of heat absorbed or released during chemical changes.

thermocouple.
A device that senses temperature changes by using a pair of joined wires made of dissimilar metals that produces a voltage that changes with temperature.

thermodynamic equilibrium.
A system* is at thermodynamic equilibrium if the energy it gains from its surroundings is exactly balanced by the energy it loses, no matter how much time is allowed to pass.

thermodynamics. thermodynamic.
The study of energy* transfers and transformations.

thermoelectron.
An electron emitted by a very hot object.

thermometer.
An instrument for measuring temperature.

thermometry.
The science of temperature* measurement.

thermoplastic. Compare with thermosetting*.
A polymer that softens or melts on heating, and becomes rigid again on cooling. Thermoplastic polymer chains are not cross-linked. Polystyrene is a thermoplastic.

thermosetting. thermosetting plastic. Compare with thermoplastic*.
A polymer that solidifies on heating and cannot be remelted. The setting action results from crosslinking of the polymer chains at high temperature- a process that is not reversed by cooling and reheating.

thin layer chromatography. (TLC) Compare with chromatography*.
A technique for separating components in a mixture on the basis of their differing polarities. A spot of sample is placed on a flat sheet coated with silica and then carried along by a solvent that soaks the sheet. Different components will move different distances over the surface. TLC is a useful screening technique in clinical chemistry; for example, it can be used to detect the presence of drugs in urine.

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-.

third law. third law of thermodynamics.
The entropy* of a perfect crystal* is zero at absolute zero*.

thixotropic fluid. thixotropy.
A liquid that becomes less viscous* when stirred. Paint and printing inks are thixotropic fluids; they are formulated so that they flow more freely when brushed or rolled.

-amino-ß%3b-hydroxybutyric%20acid">threonine. (CH3CH(OH)CH(NH2)COOH) alpha-amino-ß-hydroxybutyric acid.
A naturally occuring amino acid with a hydroxyl* group on its side chain. Closely related to serine*.

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*).

torr. Torr; mm Hg. Compare with barometer* and pressure*.
A unit of pressure*, defined so that 760 Torr is exactly 1 atmosphere*. A Torr is equivalent to 1 mm Hg on barometer* readings taken at 0°C; at other temperatures, the conversion from mm Hg to Torr is approximately p(Torr) = p(mm Hg) × (1 - 1.8×10-4t), where t is in °C.

toxicology.
The study of poisons, including identification, isolation, biological effects, mechanism of action, and development of antidotes.

transmittance. (T) percent transmittance; transmission. Compare with absorbance*.
The transmittance is the fraction of radiant intensity* transmitted by a sample,

T = I/I0

where T is the transmittance and I, I0 are the radiant intensity of the radiation after and before passing through the sample. The percent transmittance is the transmittance times 100%.

transition metal. transition element; outer transition element.
An element with an incomplete d subshell. Elements which have common cations* with incomplete d subshells are also considered transition metals. Elements with incomplete f subshells are sometimes called "inner transition elements".

transuranium element. transuranic; transuranic element.
An element with an atomic number higher than 92 (uranium's atomic number). Transuranium elements are unstable and occur in extremely low concentrations (if at all) in nature. Most are made artificially.

triglyceride.
A triglyceride is an ester* of glycerol* and three fatty acids*. Most animal fats are composed primarily of triglycerides. In the structures below, the fatty acids attached to the glycerol are represented by 'R'. The fatty acids can be the same or different.

trigonal bipyramidal. trigonal bipyramidal shape; trigonal bipyramidal geometry.
A molecular shape that results when there are five bonds and no lone pairs* on the central atom in the molecule. Three of the bonds are arranged along the atom's equator, with 120° angles between them; the other two are placed at the atom's axis. Axial bonds are at right angles to the equatorial bonds. The PCl5 molecule has a trigonal bipyramidal molecular geometry.

trigonal planar.
A molecular shape that results when there are three bonds and no lone pairs* around the central atom in the molecule. The pairs are arranged along the central atom's equator, with 120° angles between them. The carbonate ion (CO32-) has a trigonal planar geometry.

trigonal pyramidal.
A molecular shape that results when there are three bonds and one lone pair* on the central atom in the molecule. NH3 is a trigonal pyramidal molecule.

triple bond. (ident)
A covalent bond* that involves 3 bonding pairs. In the valence bond theory*, one of the bonds in a triple bond is a sigma bond* and the other two are pi bonds*. For example, the central bond in acetylene is a triple bond: H-CidentC-H.

triple point.
The temperature and pressure at which the solid, liquid, and gaseous forms of a substance are at equilibrium*.

tritium.
A radioisotope* of hydrogen with two neutrons* and one proton* in its nucleus*.

trueness. Compare with accuracy*.
Trueness is the closeness of an average measurement to a "true" value, while accuracy* is the the closeness of a single measurement to the true value.

-amino-ß%3b-indolylpropionic%20acid">tryptophan. Trp; alpha-amino-ß-indolylpropionic acid.
A naturally occuring amino acid* with a heterocyclic* group on its side chain.

Tyndall effect.
Light passing through a colloid* is scattered by suspended particles. The light beam becomes clearly visible; this phenomenon is called the Tyndall effect. For example, car headlight beams can be seen in fog, but the beams are invisible in clear air.

-amino-ß%3b-p-hydroxyphenylpropionic%20acid">tyrosine. Tyr; alpha-amino-ß-p-hydroxyphenylpropionic acid.
A naturally occuring amino acid* with a phenol* group on its side chain.



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General Chemistry Online! Glossary: T

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 02/15/10.URL: http://antoine.frostburg.edu/chem/senese/101/glossary/t.shtml