The Info List - Molecule

--- Advertisement ---

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.[4][5][6][7][8] Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions. In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules as they are monoatomic molecules.[9] A molecule may be homonuclear, that is, it consists of atoms of one chemical element, as with oxygen (O2); or it may be heteronuclear, a chemical compound composed of more than one element, as with water (H2O). Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are generally not considered single molecules.[10] Molecules as components of matter are common in organic substances (and therefore biochemistry). They also make up most of the oceans and atmosphere. However, the majority of familiar solid substances on Earth, including most of the minerals that make up the crust, mantle, and core of the Earth, contain many chemical bonds, but are not made of identifiable molecules. Also, no typical molecule can be defined for ionic crystals (salts) and covalent crystals (network solids), although these are often composed of repeating unit cells that extend either in a plane (such as in graphene) or three-dimensionally (such as in diamond, quartz, or sodium chloride). The theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses (solids that exist in a vitreous disordered state), atoms may also be held together by chemical bonds with no presence of any definable molecule, nor any of the regularity of repeating units that characterizes crystals.


1 Molecular science 2 History and etymology 3 Bonding

3.1 Covalent 3.2 Ionic

4 Molecular size 5 Molecular formulas

5.1 Chemical formula
Chemical formula
types 5.2 Structural formula

6 Molecular geometry 7 Molecular spectroscopy 8 Theoretical aspects 9 See also 10 References 11 External links

Molecular science[edit] The science of molecules is called molecular chemistry or molecular physics, depending on whether the focus is on chemistry or physics. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. In practice, however, this distinction is vague. In molecular sciences, a molecule consists of a stable system (bound state) composed of two or more atoms. Polyatomic ions may sometimes be usefully thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i.e., short-lived assemblies (resonances) of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or systems of colliding atoms as in Bose–Einstein condensate. History and etymology[edit] Main article: History of molecular theory According to Merriam-Webster
and the Online Etymology Dictionary, the word "molecule" derives from the Latin
"moles" or small unit of mass.

(1794) – "extremely minute particle", from French molécule (1678), from New Latin
molecula, diminutive of Latin
moles "mass, barrier". A vague meaning at first; the vogue for the word (used until the late 18th century only in Latin
form) can be traced to the philosophy of Descartes.[11][12]

The definition of the molecule has evolved as knowledge of the structure of molecules has increased. Earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties.[13] This definition often breaks down since many substances in ordinary experience, such as rocks, salts, and metals, are composed of large crystalline networks of chemically bonded atoms or ions, but are not made of discrete molecules.

Bonding[edit] Molecules are held together by either covalent bonding or ionic bonding. Several types of non-metal elements exist only as molecules in the environment. For example, hydrogen only exists as hydrogen molecule. A molecule of a compound is made out of two or more elements.[14] Covalent[edit] Main article: Covalent bonding

A covalent bond forming H2 (right) where two hydrogen atoms share the two electrons

A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are termed shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is termed covalent bonding.[15]

Ionic[edit] Main article: Ionic bonding

and fluorine undergoing a redox reaction to form sodium fluoride. Sodium
loses its outer electron to give it a stable electron configuration, and this electron enters the fluorine atom exothermically.

Ionic bonding
Ionic bonding
is a type of chemical bond that involves the electrostatic attraction between oppositely charged ions, and is the primary interaction occurring in ionic compounds. The ions are atoms that have lost one or more electrons (termed cations) and atoms that have gained one or more electrons (termed anions).[16] This transfer of electrons is termed electrovalence in contrast to covalence. In the simplest case, the cation is a metal atom and the anion is a nonmetal atom, but these ions can be of a more complicated nature, e.g. molecular ions like NH4+ or SO42−. Basically, an ionic bond is the transfer of electrons from a metal to a non-metal for both atoms to obtain a full valence shell.

Molecular size[edit] Most molecules are far too small to be seen with the naked eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. Molecules commonly used as building blocks for organic synthesis have a dimension of a few angstroms (Å) to several dozen Å, or around one billionth of a meter. Single molecules cannot usually be observed by light (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an atomic force microscope. Some of the largest molecules are macromolecules or supermolecules. The smallest molecule is the diatomic hydrogen (H2), with a bond length of 0.74 Å.[17] Effective molecular radius is the size a molecule displays in solution.[18][19] The table of permselectivity for different substances contains examples. Molecular formulas[edit] Chemical formula
Chemical formula
types[edit] Main article: Chemical formula The chemical formula for a molecule uses one line of chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, and plus (+) and minus (−) signs. These are limited to one typographic line of symbols, which may include subscripts and superscripts. A compound's empirical formula is a very simple type of chemical formula.[20] It is the simplest integer ratio of the chemical elements that constitute it.[21] For example, water is always composed of a 2:1 ratio of hydrogen to oxygen atoms, and ethyl alcohol or ethanol is always composed of carbon, hydrogen, and oxygen in a 2:6:1 ratio. However, this does not determine the kind of molecule uniquely – dimethyl ether has the same ratios as ethanol, for instance. Molecules with the same atoms in different arrangements are called isomers. Also carbohydrates, for example, have the same ratio (carbon:hydrogen:oxygen= 1:2:1) (and thus the same empirical formula) but different total numbers of atoms in the molecule. The molecular formula reflects the exact number of atoms that compose the molecule and so characterizes different molecules. However different isomers can have the same atomic composition while being different molecules. The empirical formula is often the same as the molecular formula but not always. For example, the molecule acetylene has molecular formula C2H2, but the simplest integer ratio of elements is CH. The molecular mass can be calculated from the chemical formula and is expressed in conventional atomic mass units equal to 1/12 of the mass of a neutral carbon-12 (12C isotope) atom. For network solids, the term formula unit is used in stoichiometric calculations.

Structural formula[edit] Main article: Structural formula

3D (left and center) and 2D (right) representations of the terpenoid molecule atisane

For molecules with a complicated 3-dimensional structure, especially involving atoms bonded to four different substituents, a simple molecular formula or even semi-structural chemical formula may not be enough to completely specify the molecule. In this case, a graphical type of formula called a structural formula may be needed. Structural formulas may in turn be represented with a one-dimensional chemical name, but such chemical nomenclature requires many words and terms which are not part of chemical formulas.

Molecular geometry[edit] Main article: Molecular geometry

Structure and STM image of a "cyanostar" dendrimer molecule.[22]

Molecules have fixed equilibrium geometries—bond lengths and angles— about which they continuously oscillate through vibrational and rotational motions. A pure substance is composed of molecules with the same average geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine its properties, particularly its reactivity. Isomers
share a chemical formula but normally have very different properties because of their different structures. Stereoisomers, a particular type of isomer, may have very similar physico-chemical properties and at the same time different biochemical activities. Molecular spectroscopy[edit] Main article: Spectroscopy

can be removed from individual H2TPP molecules by applying excess voltage to the tip of a scanning tunneling microscope (STM, a); this removal alters the current-voltage (I-V) curves of TPP molecules, measured using the same STM tip, from diode like (red curve in b) to resistor like (green curve). Image (c) shows a row of TPP, H2TPP and TPP molecules. While scanning image (d), excess voltage was applied to H2TPP at the black dot, which instantly removed hydrogen, as shown in the bottom part of (d) and in the rescan image (e). Such manipulations can be used in single-molecule electronics.[23]

Molecular spectroscopy deals with the response (spectrum) of molecules interacting with probing signals of known energy (or frequency, according to Planck's formula). Molecules have quantized energy levels that can be analyzed by detecting the molecule's energy exchange through absorbance or emission.[24] Spectroscopy
does not generally refer to diffraction studies where particles such as neutrons, electrons, or high energy X-rays interact with a regular arrangement of molecules (as in a crystal). Microwave spectroscopy commonly measures changes in the rotation of molecules, and can be used to identify molecules in outer space. Infrared spectroscopy
Infrared spectroscopy
measures changes in vibration of molecules, including stretching, bending or twisting motions. It is commonly used to identify the kinds of bonds or functional groups in molecules. Changes in the arrangements of electrons yield absorption or emission lines in ultraviolet, visible or near infrared light, and result in colour. Nuclear resonance spectroscopy actually measures the environment of particular nuclei in the molecule, and can be used to characterise the numbers of atoms in different positions in a molecule. Theoretical aspects[edit] The study of molecules by molecular physics and theoretical chemistry is largely based on quantum mechanics and is essential for the understanding of the chemical bond. The simplest of molecules is the hydrogen molecule-ion, H2+, and the simplest of all the chemical bonds is the one-electron bond. H2+ is composed of two positively charged protons and one negatively charged electron, which means that the Schrödinger equation
Schrödinger equation
for the system can be solved more easily due to the lack of electron–electron repulsion. With the development of fast digital computers, approximate solutions for more complicated molecules became possible and are one of the main aspects of computational chemistry. When trying to define rigorously whether an arrangement of atoms is sufficiently stable to be considered a molecule, IUPAC suggests that it "must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state".[4] This definition does not depend on the nature of the interaction between the atoms, but only on the strength of the interaction. In fact, it includes weakly bound species that would not traditionally be considered molecules, such as the helium dimer, He2, which has one vibrational bound state[25] and is so loosely bound that it is only likely to be observed at very low temperatures. Whether or not an arrangement of atoms is sufficiently stable to be considered a molecule is inherently an operational definition. Philosophically, therefore, a molecule is not a fundamental entity (in contrast, for instance, to an elementary particle); rather, the concept of a molecule is the chemist's way of making a useful statement about the strengths of atomic-scale interactions in the world that we observe.

See also[edit]

Atom Chemical polarity Covalent bond Diatomic
molecule List of compounds List of interstellar and circumstellar molecules Molecular biology Molecular design software Molecular engineering Molecular geometry Molecular Hamiltonian Molecular ion Molecular modelling Molecular orbital Non-covalent bonding Periodic systems of small molecules Small molecule Comparison of software for molecular mechanics modeling Van der Waals molecule World Wide Molecular Matrix

Chemistry portal Molecular and cell biology portal Physics portal


^ Iwata, Kota; Yamazaki, Shiro; Mutombo, Pingo; Hapala, Prokop; Ondráček, Martin; Jelínek, Pavel; Sugimoto, Yoshiaki (2015). "Chemical structure imaging of a single molecule by atomic force microscopy at room temperature". Nature Communications. 6: 7766. Bibcode:2015NatCo...6E7766I. doi:10.1038/ncomms8766. PMC 4518281 . PMID 26178193.  ^ Dinca, L. E.; De Marchi, F.; MacLeod, J. M.; Lipton-Duffin, J.; Gatti, R.; Ma, D.; Perepichka, D. F.; Rosei, F. (2015). " Pentacene
on Ni(111): Room-temperature molecular packing and temperature-activated conversion to graphene". Nanoscale. 7 (7): 3263–9. Bibcode:2015Nanos...7.3263D. doi:10.1039/C4NR07057G. PMID 25619890.  ^ Hapala, Prokop; Švec, Martin; Stetsovych, Oleksandr; Van Der Heijden, Nadine J.; Ondráček, Martin; Van Der Lit, Joost; Mutombo, Pingo; Swart, Ingmar; Jelínek, Pavel (2016). "Mapping the electrostatic force field of single molecules from high-resolution scanning probe images". Nature Communications. 7: 11560. Bibcode:2016NatCo...711560H. doi:10.1038/ncomms11560. PMC 4894979 . PMID 27230940.  ^ a b IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "Molecule". ^ Ebbin, Darrell D. (1990). General Chemistry (3rd ed.). Boston: Houghton Mifflin Co.
Houghton Mifflin Co.
ISBN 0-395-43302-9.  ^ Brown, T.L.; Kenneth C. Kemp; Theodore L. Brown; Harold Eugene LeMay; Bruce Edward Bursten (2003). Chemistry – the Central Science (9th ed.). New Jersey: Prentice Hall. ISBN 0-13-066997-0.  ^ Chang, Raymond (1998). Chemistry (6th ed.). New York: McGraw Hill. ISBN 0-07-115221-0.  ^ Zumdahl, Steven S. (1997). Chemistry (4th ed.). Boston: Houghton Mifflin. ISBN 0-669-41794-7.  ^ Chandra, Sulekh (2005). Comprehensive Inorganic Chemistry. New Age Publishers. ISBN 81-224-1512-1.  ^ "Molecule". Encyclopædia Britannica. 22 January 2016. Retrieved 23 February 2016.  ^ Harper, Douglas. "molecule". Online Etymology Dictionary. Retrieved 2016-02-22.  ^ "molecule". Merriam-Webster. Retrieved 22 February 2016.  ^ Molecule
Definition (Frostburg State University) ^ "The Hutchinson unabridged encyclopedia with atlas and weather guide". worldcat.org. Oxford, England. Retrieved 28 February 2016.  ^ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. Retrieved 2012-02-05.  ^ Campbell, Flake C. (2008-01-01). Elements of Metallurgy and Engineering Alloys. ASM International. ISBN 9781615030583.  ^ Roger L. DeKock; Harry B. Gray; Harry B. Gray (1989). Chemical structure and bonding. University Science Books. p. 199. ISBN 0-935702-61-X.  ^ Chang RL; Deen WM; Robertson CR; Brenner BM (1975). "Permselectivity of the glomerular capillary wall: III. Restricted transport of polyanions". Kidney Int. 8 (4): 212–218. doi:10.1038/ki.1975.104. PMID 1202253.  ^ Chang RL; Ueki IF; Troy JL; Deen WM; Robertson CR; Brenner BM (1975). "Permselectivity of the glomerular capillary wall to macromolecules. II. Experimental studies in rats using neutral dextran". Biophys. J. 15 (9): 887–906. Bibcode:1975BpJ....15..887C. doi:10.1016/S0006-3495(75)85863-2. PMC 1334749 . PMID 1182263.  ^ Wink, Donald J.; Fetzer-Gislason, Sharon; McNicholas, Sheila (2003-03-01). The Practice of Chemistry. Macmillan. ISBN 9780716748717.  ^ "ChemTeam: Empirical Formula". www.chemteam.info. Retrieved 2017-04-16.  ^ Hirsch, Brandon E.; Lee, Semin; Qiao, Bo; Chen, Chun-Hsing; McDonald, Kevin P.; Tait, Steven L.; Flood, Amar H. (2014). "Anion-induced dimerization of 5-fold symmetric cyanostars in 3D crystalline solids and 2D self-assembled crystals". Chemical Communications. 50 (69): 9827–30. doi:10.1039/C4CC03725A. PMID 25080328.  ^ Zoldan, V. C.; Faccio, R; Pasa, A. A. (2015). "N and p type character of single molecule diodes". Scientific Reports. 5: 8350. Bibcode:2015NatSR...5E8350Z. doi:10.1038/srep08350. PMC 4322354 . PMID 25666850.  ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "Spectroscopy". ^ Anderson JB (May 2004). "Comment on "An exact quantum Monte Carlo calculation of the helium-helium intermolecular potential" [J. Chem. Phys. 115, 4546 (2001)]". J Chem Phys. 120 (20): 9886–7. Bibcode:2004JChPh.120.9886A. doi:10.1063/1.1704638. PMID 15268005. 

External links[edit]

Find more aboutMoleculeat's sister projects

Definitions from Wiktionary Media from Wikimedia Commons Quotations from Wikiquote Data from Wikidata

of the Month – School of Chemistry, University of Bristol

v t e

Into matter

Macroscopic object > Molecule > Atom > Subatomic particle
Subatomic particle
(Composite particle Elementary particle)

v t e

Molecules detected in outer space



Aluminium monochloride Aluminium monofluoride Aluminium monoxide Argonium Carbon
monophosphide Carbon
monosulfide Carbon
monoxide Carborundum Cyanogen
radical Diatomic
carbon Fluoromethylidynium Hydrogen
chloride Hydrogen
fluoride Hydrogen
(molecular) Hydroxyl radical Iron(II) oxide Magnesium monohydride cation Methylidyne radical Nitric oxide Nitrogen
(molecular) Nitrogen
monohydride Nitrogen
sulfide Oxygen
(molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon mononitride Silicon monoxide Silicon monosulfide Sodium
chloride Sodium
iodide Sulfur monohydride Sulfur monoxide Titanium oxide


Aluminium hydroxide Aluminium isocyanide Amino radical Carbon
dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen
cyanide (HCN) Hydrogen
isocyanide (HNC) Hydrogen
sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene radical N2H+ Nitrous oxide Nitroxyl Ozone Phosphaethyne Potassium cyanide Protonated molecular hydrogen Sodium
cyanide Sodium
hydroxide Silicon carbonitride c-Silicon dicarbide Silicon naphthalocyanine Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Water

Four atoms

Acetylene Ammonia Cyanic acid Cyanoethynyl Cyclopropynylidyne Formaldehyde Fulminic acid HCCN Hydrogen
peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methylene amidogen Methyl radical Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thioformaldehyde Tricarbon
monoxide Tricarbon
sulfide Thiocyanic acid

Five atoms

ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy
radical Methylenimine Propadienylidene Protonated formaldehyde Protonated formaldehyde Silane Silicon-carbide cluster

Six atoms

Acetonitrile Cyanobutadiynyl radical E-Cyanomethanimine Cyclopropenone Diacetylene Ethylene Formamide HC4N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene

Seven atoms

Acetaldehyde Acrylonitrile

Vinyl cyanide

Cyanodiacetylene Ethylene
oxide Hexatriynyl radical Methylacetylene Methylamine Methyl isocyanate Vinyl alcohol

Eight atoms

Acetic acid Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Heptatrienyl radical Hexapentaenylidene Methylcyanoacetylene Methyl formate Propenal

Nine atoms

Acetamide Cyanohexatriyne Cyanotriacetylene Dimethyl ether Ethanol Methyldiacetylene Octatetraynyl radical Propene Propionitrile

Ten atoms or more

Acetone Benzene Benzonitrile Buckminsterfullerene
(C60 fullerene, buckyball) C70 fullerene Cyanodecapentayne Cyanopentaacetylene Cyanotetra-acetylene Ethylene
glycol Ethyl formate Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propanal n-Propyl cyanide Pyrimidine

Deuterated molecules

Ammonia Ammonium
ion Formaldehyde Formyl radical Heavy water Hydrogen
cyanide Hydrogen
deuteride Hydrogen
isocyanide Methylacetylene N2D+ Trihydrogen cation


Anthracene Dihydroxyacetone Ethyl methyl ether Glycine Graphene H2NCO+ Linear C5 Naphthalene
cation Phosphine Pyrene Silylidine


Abiogenesis Astrobiology Astrochemistry Atomic and molecular astrophysics Chemical formula Circumstellar envelope Cosmic dust Cosmic ray Cosmochemistry Diffuse interstellar band Earliest known life forms Extraterrestrial life Extraterrestrial liquid water Forbidden mechanism Helium
hydride ion Homochirality Intergalactic dust Interplanetary medium Interstellar medium Photodissociation region Iron–sulfur world theory Kerogen Molecules in stars Nexus for Exoplanet System Science Organic compound Outer space PAH world hypothesis Panspermia Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon
(PAH) RNA world hypothesis Spectroscopy Tholin

Book:Chemistry Category:Astrochemistry Category:Molecules Portal:Astrobiology Portal:Astronomy Portal:Chemistry

v t e

Particles in physics




Up (quark antiquark) Down (quark antiquark) Charm (quark antiquark) Strange (quark antiquark) Top (quark antiquark) Bottom (quark antiquark)


Electron Positron Muon Antimuon Tau Antitau Electron
neutrino Electron
antineutrino Muon
neutrino Muon
antineutrino Tau neutrino Tau antineutrino



Photon Gluon W and Z bosons


Higgs boson






Gluino Gravitino Photino


Higgsino Neutralino Chargino Axino Sfermion (Stop squark)


Planck particle Axion Dilaton Dual graviton Graviton Leptoquark Majoron Majorana fermion Magnetic monopole Preon Sterile neutrino Tachyon W′ and Z′ bosons X and Y bosons



Baryons / hyperons


Proton Antiproton Neutron Antineutron

Delta baryon Lambda baryon Sigma baryon Xi baryon Omega baryon

Mesons / quarkonia

Pion Rho meson Eta and eta prime mesons Phi meson J/psi meson Omega meson Upsilon meson Kaon B meson D meson

Exotic hadrons

Tetraquark Pentaquark


Atomic nuclei Atoms Exotic atoms

Positronium Muonium Tauonium Onia

Superatoms Molecules


Hypothetical baryons

Hexaquark Skyrmion

Hypothetical mesons

Glueball Theta meson T meson


Mesonic molecule Pomeron Diquarks


Davydov soliton Dropleton Exciton Hole Magnon Phonon Plasmaron Plasmon Polariton Polaron Roton Trion


Baryons Mesons Particles Quasiparticles Timeline of particle discoveries


History of subatomic physics


Standard Model

mathematical formulation

Subatomic particles Particles Antiparticles Nuclear physics Eightfold Way


Exotic matter Massless particle Relativistic particle Virtual particle Wave–particle duality


Hadronic Matter Particles of the Standard Model Leptons Quarks

Physics portal

Authority control

GND: 40399