~~Molecular Composition and Size
Molecular Composition and Size - раздел Образование, Part One THE PREDICATE Molecules Are Chemical Units Composed Of One Or More Atoms. The Simplest Mole...
Molecules are chemical units composed of one or more atoms. The simplest molecules contain one atom each; for example, helium atoms (one atom per molecule) arc identical with helium molccules. Oxygen fenoleculcs (О?) are composed of two atoms, and ozone (O3) of three. Molecules may contain several different sorts of atoms. Water (H20) contains two different kinds, hydrogen and oxygen, and dimethyl amine ((CH^NH) has three kinds. Molecules of many common gases (hydrogen H2, oxygen O2, nitrogen N2, and chlorine С12) consist of two atoms cach.
Not all molcculcs are molecular in structure. Some are atomic and many are ionic. Molecular substances are characterized by low boiling points and poor conductivity of electricity when dissolved or melted. Gases are generally molecular, and so arc many liquids, and some solids. All compounds of hydrogen and non-metallic oxides arc molecular. These compounds are considered to be bonded by a force callcd a covalent bond (or bonds) which consists of one or more shared electron pairs.
The size of molecules, especially of the smaller ones, is so tiny that to make a meaningful comparison is rather difficult. Let us assume that the water molcculcs in a cup of water are dyed so that they can be identified. If this cup had been thrown into the ocean 2,000 years ago, these molccules would have become distributed evenly in all bodies of water on the earth.
A cup of water taken at random from your nearest supply, would give you at least one hundred of the original dyed molecules. The exceedingly large number of molcculcs of water in a cup is, of course, dircctly related to the fact that cach molcculc is exceedingly small. Molcculcs are too small to be visible in ordinary light. The most powerful and best illuminated optical microscope has failed to reveal molcculcs by dircct vision, although it is claimcd that they have been resolved in the electron microscopc.
