These figures express number of billionths of a meter.
An atom is an indivisible particle of an element, and goes to make up the molecule.
(4) Chemical Notation.—The symbols used to represent the different elements (e.g. H for hydrogen, O for oxygen, etc.), when used in chemical compounds, refer to the number of atoms which go to make up the molecule of that particular compound. For example, the expression H2SO4 means that in one molecule of that acid there are 2 atoms of hydrogen, 1 of sulphur, and 4 of oxygen.
(5) Molecular Weights.—To determine the molecular weight of a compound it is necessary to know Avogadro’s Law: Equal volumes of all gases under the same conditions contain the same number of molecules; and Molecular Weight = Vapor Density × 2.
(6) Reactions.—A reaction or chemical equation is a method of representing a chemical change.
In chemistry we have three kinds of reactions, namely:
(1) Analytical reaction, which is the breaking up of compound bodies into simple, e.g., H2CO3 can be broken up into its components, H2O and CO2, e.g., H2CO3 = H2O + CO2.
(2) Synthetical reaction is the building up of a compound body by the union of two or more simple bodies, e.g., H2 + O = H2O and H + Cl = HCl.
(3) Metathetical reaction consists in the interchange of two radicals in two substances, e.g.,