A system of physical chemistry - Index of

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A system of physical chemistry - Index of

6o A SYSTEM OF PHYSICAL CHEMISTRY

I / ne'-

''violet = — a/ 5

2:r \ tnr'

where « is the " valency," e the charge on an electron (in electostatic

units), m the mass of an electron, and rone half of the distance between

the centres of two neighbouring atoms.

Lindemann introduces an expression due to Haber and discussed

later

(p. 133), which connects the ultra-violet frequency with the characteristic

infra-red frequency, Vred, the relation being—

''violet

where m is the mass of an electron, and M the actual mass of the

atom. Combining this expression with that given above we obtain—

J'red = — 27r

Further, if A is the atomic weight, N the number of atoms in one gramatom,

and d the density of the substance, then Lindemann shows

that—

Hence,

r = V^

M

n

^.N

''red = t.h N Jdn

A

But fN = F = the Faraday = 2-9 x lo^* electrostatic units.

Hence, ''red i'o95

X 10 14 Jd. 11

By means of a suitable choice of n we can calculate the infra-red

frequency of an element from this formula. The calculated values

agree with those observed, in some cases better than do those values

obtained by the melting point method. There is a certain arbitrariness,

however, in the choice of the valency «, as will be seen from the following

table which is quoted from Lindemann's paper :—

Element.

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