Hydrogen 20.3
Nitrogen 29.1
Oxygen 27.3
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._,
2HCl + Zn = ZnCl₂ + H₂. Here the H of the acid is replaced by the Zn.
KCl + AgNO₃ = AgCl + KNO₃. Here the Ag and the K change places.
(7) THE CHEMICAL ARITHMETIC by which from the molecular weights of two
substances, and the weight of one substance we are enabled to get the
weight of the required substance is called Stoichiometry.
EXAMPLE: Required the amount of zinc necessary to generate 10 grams of
hydrogen.
Atomic weights of H, Cl, and Zn are respectively 1, 35.5, and 65.3.