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Chemical Glossary - Definitions of Chemical Terms

NOTE:The letter R is used to represent an arbitrary radical.
See also the Geology Glossary.

Acid - 1) A substance with a sour taste. 2) A substance that yields hydrogen ions when dissolved in water (compare with base). 3) A compound containing a carboxyl group (-COOH).
Acid group

Acyl - A radical having the general formula RCO-, derived from an organic acid by the removal of the OH group.

Alcohol - 1) A compound containing a hydroxyl group (-OH).  2) The common name of ethyl alcohol or grain alcohol (CH3CH2OH)
R-OH

Aldehyde - A compound containing an aldehyde group (-CHO).
Aldehyde radical

Aliphatic - An organic compound that does not contain ring structures.

Alkane - A saturated carbon compound with the general formula CnH2n+2. The first five alkanes (n=1 to 5) are: methane, ethane, propane, butane, and pentane.

CH3-CH2-CH2-CH3 
Butane

Alkene - A compound consisting of only carbon and hydrogen, that contains at least one carbon-carbon double bond and is thereby unsaturated. Example: Ethylene (CH2=CH2)

Alkyl - A molecular fragment of an alkane from which one hydrogen atom has been removed, and has the general formula CnH2n+1. Examples: methyl (-CH3), ethyl (-CH2CH3).

Alkyne - A compound that consists of only carbon and hydrogen containing at least one carbon-carbon triple bond.

Amide - An organic compound containing a carbonyl group bound to nitrogen: R-(C=O)NH2.

Amine - A compound containing an amino group (-NH2).
R-NH2

Amino Acid - A compound with amino and carboxyl groups that is a constituent of peptides and proteins.
Amino Acid
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Aromatic Compound - An organic molecule containing at least one benzene ring.
Benzene
Benzene

Atom - The smallest component of an element that still has properties of the element, consisting of a positively charged nucleus, and surrounded by a charged cloud of electrons. The nucleus contains protons and may contain neutrons. (See Periodic Table, below)

Examples of atoms.

Atomic Number - The number of protons in a nucleus. It determines the chemical properties of an element.

Atomic Weight - The atomic mass of an atom relative to 1/12 of the mass of the Carbon-12 isotope.

Base - A substance that accepts hydrogen ions when dissolved in water (compare with acid).

Bond - The attraction of atoms to each other through sharing or exchanging electrons.

Carbohydrate - A term used for sugars and sugar derivatives that contain only carbon, hydrogen, and oxygen, usually in the ratio 1:2:1
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Carbonyl Group - A chemical group consisting of carbon and oxygen (C=O). (See also ketone)

Carboxyl Group - The group (-COOH) found in acids (see Acid).

Chemical Compound - A substance consisting of two or more elements chemically bonded together in a fixed proportion by mass.

Cyclic Compound - A chemical compound forming a ring.

Covalent Bond - A chemical bond formed by the sharing of electrons between atoms.

Electron - A negatively charged particle (-1) with a mass 1/1837 of that of a proton.

Element - Matter composed of atoms that all have the same atomic number (protons).

Ester - The product of an organic acid and an alcohol.
Ester group

Ether - A compound containing two organic radicals linked by an oxygen atom.
Ether structure

Ethyl - The organic group derived from ethane CH3CH2-. See Alkyl.


Fat - 1) A compound consisting of glycerol and fatty acids. 2) A triglyceride.
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Fatty Acid - An organic acid usually found in fats. Click here for a detailed description.

Halogen - The elements of Group 17 (VIIA) of the periodic table: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

Heterocyclic Compound - A compound with a ring that contains non-carbon atoms.
Purine
Purine - A heterocyclic compound

Hydrocarbon - Any organic compound, such as benzene and methane, that contain only carbon and hydrogen.

Hydroxyl Group - A chemical group containing one hydrogen and one oxygen (-OH)

Inorganic compound - A chemical compound that does not contain carbon.

Ion - An electrically charged atom or molecule obtained by the gain or loss of electrons.

Ionic bond or electrovalent bond, is an electrical attraction between two oppositely charged atoms or groups of atoms. Compare with covalent bond.

Isotope - An atom having the same number of protons but a different number of neutrons in its nucleus.

Ketone - A compound containing a carbonyl group (C=O).
Ketone structure

Line Formula - A chemical formula that shows atomic attachments expressed in a linear form, e.g., RCH(NH2)COOH. Compare with structural formula and molecular formula.

Methyl - The organic group derived from methane CH3-. See Alkyl.

Molecular Formula - A summary of the number of specific elements in a chemical compound that does not specify how the atoms are the atoms are attached. Example: Benzene has the molecular formula C6H6. Compare with the structural formula for benzene under Aromatic Compound.

Molecule - The smallest particle of a substance that retains the chemical and physical properties of the substance and is composed of two or more atoms.

Neutron - A non-charged nuclear particle with the same mass as the proton.

Nitrate - The radical -NO3, or a compound containing it.

Proton - A component of an atomic nucleus with a mass defined as 1 and a charge of +1.

Organic compound - A chemical compound containing carbon chemically bound to hydrogen. Other elements such as O, N, halogens, or S may be present.

Peptide - A compound consisting of 2 or more amino acids.
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Peptide bond - A peptide bond (amide bond) is a chemical bond formed between two molecules when the carboxyl group (-COOH) of one molecule reacts with the amine group (-NH2) of the other.
Peptide bond

Periodic Table - An arrangement of the elements according to their atomic numbers so that elements with similar properties are in the same column. The first periodic table was published by Dmitri Mendeleev in 1869.
Periodic Table


The symbols of some elements are derived from their Latin names (in parentheses).
Chemical element Symbol Atomic
number
Actinium Ac 89
Aluminum Al 13
Americium Am 95
Antimony (Stibium) Sb 51
Argon Ar 18
Arsenic As 33
Astatine At 85
Barium Ba 56
Berkelium Bk 97
Beryllium Be 4
Bismuth Bi 83
Bohrium Bh 107
Boron B 5
Bromine Br 35
Cadmium Cd 48
Calcium Ca 20
Californium Cf 98
Carbon C 6
Cerium Ce 58
Cesium Cs 55
Chlorine Cl 17
Chromium Cr 24
Cobalt Co 27
Copper (Cuprum) Cu 29
Curium Cm 96
Darmstadtium Ds 110
Dubnium Db 105
Dysprosium Dy 66
Einsteinium Es 99
Erbium Er 68
Europium Eu 63
Fermium Fm 100
Fluorine F 9
Francium Fr 87
Gadolinium Gd 64
Gallium Ga 31
Germanium Ge 32
Gold (Aurum) Au 79
Hafnium Hf 72
Hassium Hs 108
Helium He 2
Holmium Ho 67
Hydrogen H 1
Indium In 49
Iodine I 53
Iridium Ir 77
Iron (Ferrum) Fe 26
Krypton Kr 36
Lanthanum La 57
Lawrencium Lr 103
Lead (Plumbum) Pb 82
Lithium Li 3
Lutetium Lu 71
Magnesium Mg 12
Manganese Mn 25
Meitnerium Mt 109
Mendelevium Md 101
Chemical element Symbol Atomic
number
Mercury (Hydrargyrum) Hg 80
Molybdenum Mo 42
Neodymium Nd 60
Neon Ne 10
Neptunium Np 93
Nickel Ni 28
Niobium Nb 41
Nitrogen N 7
Nobelium No 102
Osmium Os 76
Oxygen O 8
Palladium Pd 46
Phosphorus P 15
Platinum Pt 78
Plutonium Pu 94
Polonium Po 84
Potassium (Kalium) K 19
Praseodymium Pr 59
Promethium Pm 61
Protactinium Pa 91
Radium Ra 88
Radon Rn 86
Rhenium Re 75
Rhodium Rh 45
Rubidium Rb 37
Ruthenium Ru 44
Rutherfordium Rf 104
Samarium Sm 62
Scandium Sc 21
Seaborgium Sg 106
Selenium Se 34
Silicon Si 14
Silver (Argentum) Ag 47
Sodium (Natrium) Na 11
Strontium Sr 38
Sulfur S 16
Tantalum Ta 73
Technetium Tc 43
Tellurium Te 52
Terbium Tb 65
Thallium Tl 81
Thorium Th 90
Thulium Tm 69
Tin (Stannum) Sn 50
Titanium Ti 22
Tungsten (Wolfram) W 74
Ununbium Uub 112
Ununtrium Uut 113
Unununium Uuu 111
Uranium U 92
Vanadium V 23
Xenon Xe 54
Ytterbium Yb 70
Yttrium Y 39
Zinc Zn 30
Zirconium Zr 40

Phenyl - A molecular group consisting of a benzene ring where one or more hydrogens have been replaced by other atoms or radicals. See Aromatic Compound.

Protein - A compound consisting of 50 or more amino acids.

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Saturated Compound - An organic compound, such as butane, that contains only single carbon-to-carbon bonds. The name derives from the fact that the compound cannot bind to additional hydrogen atoms, and is, therefore, "saturated" with hydrogen.
CH3-CH2-CH2-CH3
Butane

Structural Formula - A chemical structure representation that shows all the atomic attachments. Example: see Amino Acid.

Sugar - See carbohydrate

Transition element - Any element belonging to one of three series of elements with atomic numbers between 21 and 30, 39 and 48, and 57 and 80. They are characterized by multiple valences, colored compounds, and the ability to form stable complex ions.

Triglyceride - 1) Fat. 2) A compound consisting of one molecule of glycerol and three fatty acids. Also called triacylglycerol.

Unsaturated Compound - An organic compound that contains double or triple carbon-to-carbon bonds, and can theoretically bind to additional hydrogen atoms.
CH2=CH-CH2-CH3
1-Butene

Valence - The combining capacity of an atom or radical determined by the number of electrons that it will lose, add, or share when it reacts with other atoms.



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