Dictionary of Chemistry [6th Ed.]

duce fragment ions in electron-

impact impact ionization sources.

The sample is dissolved in a volatile

solvent, which may also contain

volatile acids or bases so that the

sample exists in an ionic form. The

solution is forced through a charged

metal capillary tube and forms an

aerosol. Evaporation of the solvent

results in single ions of the sample,

which are analyzed by the mass spec-

trometer. Electrospray ionization is

the ionization technique often used

in chromatography–mass spectrome-

try.

electrovalent bond See chemical

bond.

electrum1.An alloy of gold and

silver containing 55–88% of gold.

2.A *German silver alloy containing

52% copper, 26% nickel, and 22%

zinc.

elementA substance that cannot

be decomposed into simpler sub-

stances. In an element, all the atoms

have the same number of protons or

electrons, although the number of

neutrons may vary. There are 92

naturally occurring elements. See

also periodic table; transuranic el-

ements; transactinide elements.

elementary particleOne of the

fundamental particles of which mat-

ter is composed, such as the electron,

proton, or neutron.

elementary reaction A reaction

with no intermediates; i.e. one that

takes place in a single step with a sin-

gle transition state.

elevation of boiling pointAn in-

crease in the boiling point of a liquid

when a solid is dissolved in it. The el-

evation is proportional to the num-

ber of particles dissolved (molecules

or ions) and is given by ∆t = kBC,

where C is the molal concentration

of solute. The constant kBis the ebul-

lioscopic constant of the solvent and

if this is known, the molecular

weight of the solute can be calcu-

lated from the measured value of ∆t.

The elevation is measured by a Beck-

mann thermometer. See also colliga-

tive properties.

elimination reaction A reaction

in which one molecule decomposes

into two, one much smaller than the

other.

ElinvarTrade name for a nickel–

chromium steel containing about

36% nickel, 12% chromium, and

smaller proportions of tungsten and

manganese. Its elasticity does not

vary with temperature and it is

therefore used to make hairsprings

for watches.

Ellingham diagramA diagram

used to show the conditions under

which a metal oxide can be reduced

to a metal. The standard Gibbs free

energy of formation of the oxide is

considered, for example,

M + ½O 2 →MO

This value, ∆GŠ, is plotted against

temperature. In general, the result is

a straight line. In some cases, there is

an abrupt change in the line’s slope

at a point because of a phase change.

The value of ∆GŠfor the reducing

agent is also plotted. For example, if

the reducing agent is carbon forming

carbon dioxide, it is ∆GŠfor the re-

action

C + O 2 →CO 2

electrovalent bond 202

e

temperature

C + O 2 = CO 2

2M + O 2 = 2MO

CO + O 2 = 2CO 2

2C + O 2 = 2CO

free

energy

Ellingham diagram