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Text 16 A

Molecules

 

Text 16 A Molecules - раздел Образование, Part One THE PREDICATE To The Modern Chcmist, The Atom Is The Smallest Particle Of An Clement That C...

 
 

   

To the modern chcmist, the atom is the smallest particle of an clement that can enter into a chcmical reaction. Thus, each clement has atoms that are peculiar to itself and different from those of each of the other elements. Chcmical reactions occur when atoms of different kinds unite to form groups in which they bear definite relationships to cach other or when these groups undergo disruption or rearrangement. Chcmical unions arc of two general types.

In one type of union, atoms bccomc bonded together to form definite aggregates that exist as independent, electrically neutral particles and arc known as molcculcs (Latin 'little mass**). Some elements have atoms that unite with others of their own kind to form molcculcs. These arc known as elemental molcculcs and arc exemplified by the chlorinc molecule which is made up of two chlorinc atoms. Compound molcculcs arc composed of two or more kinds of atoms and arc exemplified by the water molcculc, which contains two atoms of hydrogen and one of oxygen.

To give a short definition of a molcculc is not to give a more or less full account of properties.

Molcculcs arc regarded as the smallest particlcs or elementary substanccs that can have independent existence. They account for the chcmical properties and at least some of the physical properties of the substancc they constitute. A single molcculc docs not exhibit in full the physical properties commonly associated with its particular variety of matter. These properties arise both within the molcculc itself and within the aggregates of like molcculcs that constitute a sample of the given substance. The density of water depends not only on the mass and volume of indivilual molcculcs but also on the manner in which the molcculcs arc packed together. Since the chcmist works with the aggregates, their properties arc of great practical importance.

A molcculc of a compound contains, of ncccssity, at least two different atoms. An clement molcculc may contain only one atom, or it may contain two or more. Helium has monoatomic molcculcs; chlorinc and hydrogen cach exist as diatomic molecules; and sulphur molcculcs contain eight atoms. During reactions the atoms of elemental molecules usually arc separated and individually redistributed in new combinations.


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