3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. Three-dimensional space is a geometric model of the physical Universe in which we live A 2D geometric model is a Geometric model of an object as two-dimensional figure usually on the Euclidean or Cartesian plane. The terpenoids, sometimes referred to as isoprenoids, are a large and diverse class of naturally-occurring organic chemicals similar to Terpenes derived

In chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds . Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic It can also be defined as a unit of two or more atoms held together by covalent bonds. ^[1][2] In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules and biomolecules. Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. A biomolecule is any organic Molecule that is produced by living Organisms including large Polymeric molecules such as Proteins Molecules are distinguished from polyatomic ions in this strict sense. A polyatomic ion is a charged species ( Ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered as acting

This definition 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. This is a list of the different types of particles known and hypothesized A chemical substance is a Material with a definite chemical composition. A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. ^[3] This definition often breaks down since many substances in ordinary experience, such as rocks, salts, and metals, are composed of atoms or ions, but are not made of molecules. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere A salt, in Chemistry, is defined as the product formed from the neutralisation reaction of Acids and bases. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge

In the kinetic theory of gases the term molecule is often used for any gaseous particle regardless of their composition. Kinetic theory (or kinetic theory of gases) attempts to explain Macroscopic properties of Gases such as pressure temperature or volume by considering This page is about the physical properties of gas as a state of matter ^[4] According to this definition noble gases would also be considered molecules despite the fact that they are composed of a single non-bonded atom. History Noble gas is translated from the German noun de ''Edelgas'' first used in 1898 by Hugo Erdmann to indicate their extremely low level of reactivity

History

Main article: History of the molecule

The term "molecule", from the French molécule meaning "extremely minute particle," was coined by French philosopher Rene Descartes in the 1620s. In Chemistry, the history of the Molecule traces the origins of the concept or idea of the existence of strong chemical bonds between two or more Atoms Although the existence of molecules was accepted by many chemists since the early 19th century as a result of Dalton's laws of Definite and Multiple Proportions (1803-1808) and Avogadro's law (1811), there was some resistance among positivists and physicists such as Mach, Boltzmann, Maxwell, and Gibbs, who saw molecules merely as convenient mathematical constructs. John Dalton FRS (6 September 1766 &ndash 27 July 1844 was an English Chemist, Meteorologist and Physicist. Avogadro's law ( Avogadro's Hypothesis, or Avogadro's Principle) is a Gas law named after Amedeo Avogadro, who in 1811 hypothesized Logical positivism (later and more accurately called logical empiricism) is a school of philosophy that combines Empiricism, the idea that observational evidence is Ernst Mach (max ( February 18, 1838 &ndash February 19, 1916) was an Austrian Physicist and Philosopher and Ludwig Eduard Boltzmann ( February 20, 1844 &ndash September 5, 1906) was an Austrian Physicist famous for his founding James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. Josiah Willard Gibbs ( February 11, 1839 &ndash April 28, 1903) was an American theoretical Physicist, Chemist The work of Perrin on Brownian motion (1911) is considered to be the final proof of the existence of molecules. Jean Baptiste Perrin ( September 30, 1870 &ndash April 17, 1942) was a French Physicist and Nobel laureate.

In a molecule, at least two atoms are joined by shared pairs of electrons in a covalent bond. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J It may consist of atoms of the same chemical element, as with oxygen (O₂), or of different elements, as with water (H₂O). A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic bonds are generally not considered single molecules. A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen An ionic bond (or electrovalent bond) is a type of Chemical bond that can often form between Metal and Non-metal Ions (or

No typical molecule can be defined for ionic (salts) and covalent crystals (network solids) which are composed of repeating unit cells that extend either in a plane (such as in graphite) or three-dimensionally (such as in diamond or sodium chloride). A salt, in Chemistry, is defined as the product formed from the neutralisation reaction of Acids and bases. In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in For sodium chloride in the diet see Salt. Sodium chloride, also known as common salt, table salt, or Halite, is a

The science of molecules is called molecular chemistry or molecular physics, depending on the focus. Molecular physics is the study of the physical properties of Molecules and of the Chemical bonds between Atoms that bind them 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. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic In practice, however, this distinction is vague. In molecular sciences, a molecule consists of a stable system (bound state) comprising two or more atoms. In Physics, a bound state is a composite of two or more building blocks ( particles or bodies) that behaves as a single object History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Polyatomic ions may sometimes be usefully thought of as electrically charged molecules. A polyatomic ion is a charged species ( Ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered as acting 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 condensates. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge A Rydberg atom is an excited atom with one or more Electrons that have a very high Principal quantum number. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. The Van der Waals equation is an Equation of state that can be derived from a special form of the potential between a pair of molecules (hard-sphere repulsion A Bose–Einstein condensate (BEC is a State of matter of Bosons confined in an external Potential and cooled to Temperatures very near to

Molecular size

Most molecules are far too small to be seen with the opened eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known The term macromolecule by definition implies "large Molecule " Macroscopic is commonly used to describe physical objects that are measurable and observable by the Naked eye. The smallest molecule is the diatomic hydrogen (H₂), with an overall length of roughly twice the 74 picometres (0. Diatomic molecules are molecules made only of two Atoms of either the same or different Chemical elements The prefix di- means two in Greek Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 A picometre ( American spelling: picometer, symbol pm) is a unit of Length in the Metric system, equal to one trillionth 74 Å) bond length. An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal Molecules commonly used as building blocks for organic synthesis have a dimension of a few Å to several dozen Å. 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. The atomic force microscope (AFM or scanning force microscope (SFM is a very high-resolution type of scanning probe microscope, with demonstrated resolution of fractions Some of the largest molecules are macromolecules or supermolecules. The term macromolecule by definition implies "large Molecule " The term supermolecule or supramolecule was introduced by KL Wolf ( Übermoleküle) in 1937 to describe hydrogen bonded Acetic

Radius

Effective molecular radius is the size a molecule displays in solution. ^[5]. The table of permselectivity for different substances contains examples. This is a table of Permselectivity for different substances in the Glomerulus of the Kidney in Renal filtration.

Molecular formula

The empirical formula of a molecule is the simplest integer ratio of the chemical elements that constitute the compound. Use in chemistry In Chemistry, the empirical formula of a Chemical compound is a simple expression of the relative number of each type of Atom The integers (from the Latin integer, literally "untouched" hence "whole" the word entire comes from the same origin but via French A ratio is an expression which compares quantities relative to each other A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. For example, in their pure forms, water is always composed of a 2:1 ratio of hydrogen to oxygen, and ethyl alcohol or ethanol is always composed of carbon, hydrogen, and oxygen in a 2:6:1 ratio. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the However, this does not determine the kind of molecule uniquely - dimethyl ether has the same ratio as ethanol, for instance. Dimethyl ether is the organic compound with the formula CH3OCH3 Molecules with the same atoms in different arrangements are called isomers. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. 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. Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes The molecular formula reflects the exact number of atoms that compose a molecule. A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes

The molecular mass can be calculated from the chemical formula and is expressed in conventional atomic mass units equal to 1/12th of the mass of a neutral carbon-12 (¹²C isotope) atom. The molecular mass (abbreviated m of a substance, more commonly referred to as molecular weight and abbreviated as MW, is the Mass of one The unified atomic mass unit ( u) or Dalton ( Da) or sometimes universal mass unit, is an unit of Mass used to express Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides For network solids, the term formula unit is used in stoichiometric calculations. A formula unit in Chemistry is the Empirical formula of an ionic or Covalent Network solid compound used as an independent entity Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry is the Calculation of Quantitative (measurable

Molecular geometry

Main article: Molecular geometry

Molecules have fixed equilibrium geometries—bond lengths and angles— about which they continuously oscillate through vibrational and rotational motions. Molecular geometry or molecular structure is the three- Dimensional arrangement of the Atoms that constitute a Molecule. A pure substance is composed of molecules with the same average geometrical structure. In Mathematics, an average, or central tendency of a Data set refers to a measure of the "middle" or " expected " value of 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 isomers, may have very similar physico-chemical properties and at the same time very different biochemical activities. Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution but which differ in the three dimensional orientations Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as

Molecular spectroscopy

Main article: Spectroscopy

Molecular spectroscopy deals with the response (spectrum) of molecules interacting with probing signals of known energy (or frequency, according to Planck's formula). Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ Familiar concepts associated with a Frequency are colors musical notes radio/TV channels and even the regular rotation of the earth In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Frequency is a measure of the number of occurrences of a repeating event per unit Time. The Planck constant (denoted h\ is a Physical constant used to describe the sizes of quanta. Scattering theory provides the theoretical background for spectroscopy. In Mathematics and Physics, scattering theory is a framework for studying and understanding the Scattering of Waves and particles.

The probing signal used in spectoore can be an electromagnetic wave or a beam of particles (electrons, positrons, etc. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Particle physics, an elementary particle or fundamental particle is a particle not known to have substructure that is it is not known to be made The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. ) The molecular response can consist of signal absorption (absorption spectroscopy), the emission of another signal (emission spectroscopy), fragmentation, or chemical changes. Absorption spectroscopy refers to a range of techniques employing the interaction of electromagnetic radiation with matter Emission spectroscopy is a spectroscopic technique which examines the wavelengths of Photons emitted by atoms or molecules during their transition from an

Spectroscopy is recognized as a powerful tool in investigating the microscopic properties of molecules, in particular their energy levels. Microscopic is a term used to describe objects smaller than those that can easily be seen by the naked Eye and which require a lens or Microscope to see A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which In order to extract maximum microscopic information from experimental results, spectroscopy is often coupled with chemical computations. Computational chemistry is a branch of Chemistry that uses computers to assist in solving chemical problems

Theoretical aspects

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. Molecular physics is the study of the physical properties of Molecules and of the Chemical bonds between Atoms that bind them Theoretical chemistry involves the use of physics to explain or predict chemical phenomena Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic The simplest of molecules is the hydrogen molecule-ion, H₂⁺, and the simplest of all the chemical bonds is the one-electron bond. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic H₂⁺ is composed of two positively-charged protons and one negatively-charged electron bound by photon exchange, which means that the Schrödinger equation for the system can be solved more easily due to the lack of electron–electron repulsion. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena In Physics, especially Quantum mechanics, the Schrödinger equation is an equation that describes how the Quantum state of a Physical system 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. Computational chemistry is a branch of Chemistry that uses computers to assist in solving chemical problems

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". A potential energy surface is generally used within the adiabatic or Born–Oppenheimer approximation in Quantum mechanics and Statistical mechanics ^[1] 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 but is so loosely bound that it is only likely to be observed at very low temperatures. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical A dimer is a Chemical or Biological entity consisting of two subunits called Monomers which are held together by either Intramolecular forces In Physics, a bound state is a composite of two or more building blocks ( particles or bodies) that behaves as a single object

Etymology

According to Merriam-Webster and the Online Etymology Dictionary, the word "molecule" derives from the Latin "moles" or small unit of mass. Merriam-Webster, which was originally the G & C Merriam Company of Springfield Massachusetts, is an American company that publishes reference books The Online Etymology Dictionary is a Dictionary that describes the origins of English language words Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this

• Molecule (1794) - "extremely minute particle," from Fr. molécule (1678), from Mod. L. molecula, dim. of L. moles "mass, barrier". A vague meaning at first; the vogue for the word (used until late 18th century only in Latin form) can be traced to the philosophy of Descartes.

Most molecules are made up of multiple atoms; for example, a molecule of water is a combination of two hydrogen atoms and one oxygen atom. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The term 'molecule' in gases has been used as a synonym for the fundamental particles of the gas, whatever their structure. This definition results in a few types of gases (for example inert elements that do not form compounds, such as neon), which has 'molecules' consisting of only a single atom. Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 ^[6]

See also

• Molecular modelling
• Covalent bond
• Diatomic molecule
• History of the molecule
• Molecular geometry
• Molecular Hamiltonian
• Molecular orbital
• Chemical polarity
• For a list of molecules see the List of compounds
• List of molecules in interstellar space

References

External links

• MoleClues - Molecular science for kids
• Molecular Frontiers - Home Page of Molecular Frontiers Foundation
• Molecule of the Month - School of Chemistry, University of Bristol
• Antibody Molecule - The National Health Museum
• Data Book of Molecules - Home Page for Learning Environmental Chemistry