Atomic weights, inside back cover

Let us do a little bookkeeping with the exact masses of these nuclei. Actually we will simplify a bit and use the exact masses of the atoms. This will make no difference. The masses of the atoms differ from the nuclear masses by the masses of the number of electrons in each atom. We have shown that electrons are conserved in nuclear changes. Exact masses of atoms (that is, exact masses of each isotopic species and not the chemical atomic weights shown on the inside back cover) are readily available. For our hydrogen-helium reaction we have... 

Atomic velocity distribution, 130,131 Atomic volume, 94, 98 alkali metals, 94 halogens, 97 inert gases, 91 third-row elements, 101 Atomic weight, 33 table, inside back cover Atoms, 21 conservation of, 40 electrical nature of, 236 measuring dimensions of, 245 Avogadro, Amadeo hypothesis, 25, 52 hypothesis and kinetic theory, 58 law, 25 number, 33 Azo dyes, 344... 

There are two unknowns on the chart (mi and m2) and two independent molecular species on which balances may be written (MgS04 and H2O), so that the problem can be solved. The atomic weights on the inside back cover may be used to show that the molecular weight of anhydrous magnesium sulfate is 120.4 and that of the heptahydrate salt is 246.4. The balances follow. 

The atomic number (Z) is therefore the number of protons in the nucleus of an atom. Because you can determine the atomic number experimentally, you can determine unambiguously whether or not a sample is a pure element or if perhaps you have discovered a new element. We can now state the definition of an element with more precision than we could in Section 2.1. An element is a substance whose atoms all have the same atomic number. The inside back cover of the book lists the elements and their atomic numbers (see the Table of Atomic Numbers and Atomic Weights). 

From the Table of Atomic Numbers and Atomic Weights on the inside back cover of this book, you will note that the element with atomic number 38 (the number of protons in the nucleus) is strontium, symbol Sr. The mass number is 38 +... 

On this modem scale, the atomic we t of an element is the average atomic mass for the naturally occurring element, expressed in atomic mass units. A complete table of atomic weights appears on the inside back cover of this book. (Allhough the use of the term weight in atomic weight is not strictly correct, it is sanctioned by convention to mean average atomic mass. )... 

This average weight is the weight that all carbon atoms appear to have as they are dealt with by chemists. The average atomic weights for all the elements have been determined in a similar way, and it is these averages that are listed in the relative atomic weight scale inside the back cover. 

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