molecules

This i from me Dhafer for everyone in 4Victorious:].This is the information about heat.I copied it from this website.this is the shortcut http://en.wikipedia.org/wiki/Molecule A **molecule** is defined as an [|electrically] neutral group of at least two [|atoms] in a definite arrangement held together by very strong ([|covalent]) [|chemical bonds].[|[1]][|[2]] Molecules are distinguished from [|polyatomic ions] in this strict sense. In [|organic chemistry] and [|biochemistry], the term //molecule// is used less strictly and also is applied to charged [|organic molecules] and [|biomolecules]. 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 despite the fact that they are composed of a single non-bonded atom.[|[3]] A molecule may consist of atoms of a single [|chemical element], as with [|oxygen] (O2), or of different elements, as with [|water] (H2O). Atoms and complexes connected by non-covalent bonds such as [|hydrogen bonds] or [|ionic bonds] are generally not considered single molecules. 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] or [|sodium chloride]). The theme of repeated unit-cellular-structure also holds for most condensed phases with [|metallic bonding]. In [|glasses] (solids that exist in a vitreous disordered state), atoms may also be held together by chemical bonds without any definable molecule, but also without any of the regularity of repeating units that characterises crystals. The science of molecules is called //molecular chemistry// or //[|molecular physics]//, depending on the focus. 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]) comprising 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] 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. The smallest molecule is the [|diatomic] [|hydrogen] (H2), with an overall length of roughly twice the 74 [|picometres] (0.74 [|Å]) bond length. 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]. Some of the largest molecules are [|macromolecules] or [|supermolecules].

Radius
//Effective molecular radius// is the size a molecule displays in solution.[|[5]][|[6]] The [|table of permselectivity for different substances] contains examples.

Molecular formula
A compound's [|empirical formula] is the **simplest** [|integer] [|ratio] of the [|chemical elements] that constitute it. 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 isomers. 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 1/12th of the mass of a neutral carbon-12 (12[|C] [|isotope]) atom. For [|network solids], the term [|formula unit] is used in [|stoichiometric] calculations