CHAPTER 1 INTRODUCTION
1.1 UNITS 21
Table 1.4 SI prefixesFraction Prefix Symbol Multiple Prefix Symbol
10 ^1 deci d 10 deka da
10 ^2 centi c 102 hecto h
10 ^3 milli m 103 kilo k
10 ^6 micro ù 106 mega M
10 ^9 nano n 109 giga G
10 ^12 pico p 1012 tera T
10 ^15 femto f 1015 peta P
10 ^18 atto a 1018 exa E
10 ^21 zepto z 1021 zetta Z
10 ^24 yocto y 1024 yotta YAny of the symbols for units listed in Tables1.1–1.3, except kg andC, may be preceded
by one of the prefix symbols of Table1.4to construct a decimal fraction or multiple of the
unit. (The symbol g may be preceded by a prefix symbol to construct a fraction or multiple
of the gram.) The combination of prefix symbol and unit symbol is taken as a new symbol
that can be raised to a power without using parentheses, as in the following examples:
1 mgD 1 10 ^3 g
1 cmD 1 10 ^2 m
1 cm^3 D.1 10 ^2 m/^3 D 1 10 ^6 m^31.1.1 Amount of substance and amount
The physical quantity formally calledamount of substanceis a counting quantity for par-
ticles, such as atoms or molecules, or for other chemical entities. The counting unit is
invariably themole, defined as the amount of substance containing as many particles as the
number of atoms in exactly 12 grams of pure carbon-12 nuclide,^12 C. See AppendixAfor
the wording of the official IUPAC definition. This definition is such that one mole of H 2 O
molecules, for example, has a mass of18:0153grams (where18:0153is the relative molec-
ular mass of H 2 O) and contains6:02214 1023 molecules (where6:02214 1023 mol ^1 is
theAvogadro constantto six significant digits). The same statement can be made for any
other substance if18:0153is replaced by the appropriate atomic mass or molecular mass
value.
The symbol for amount of substance isn. It is admittedly awkward to refer ton(H 2 O)
as “the amount of substance of water.” This book simply shortens “amount of substance” to
amount, a common usage that is condoned by the IUPAC.^2 Thus, “the amount of water in
the system” refers not to the mass or volume of water, but to thenumberof H 2 O molecules
in the system expressed in a counting unit such as the mole.
(^2) Ref. [ 118 ]. An alternative name suggested fornis “chemical amount.”