preface to fifteenth edition

2.6 SECTION 2
TABLE 2.1
Fundamental Physical Constants (Continued)
D. Units in use together with SI units (continued)
Physical quantity Name of unit Symbol for unit Value in SI units
unified atomic
u[ m a ( 12 C)/12]
1.66054 10 27 kg
mass unit
dalton 3
Da
Plane angle degree (/180) rad
minute (/10 800) rad
second (/648 000) rad
Pressure bar 2 bar 10 5 Pa 10 5 Nm 2
Time minute min 60 s
hour h 3600 s
day d 86 400 s
Volume liter (litre) L, l dm 3 10 3 m 3
milliliter mL, ml cm 3 10 6 m 3
2
The ångström and bar are approved for temporary use with SI units; however, they should not be introduced if not used at
present.
3
The name dalton and symbol Da have not been approved although they are often used for large molecules.
TABLE 2.2
Physical and Chemical Symbols and Definitions
Symbols separated by commas represent equivalent recommendations. Symbols for physical and chemical quantities
should be printed in italic type. Subscripts and superscripts which are themselves symbols for physical
quantities should be italicized; all others should be in Roman type. Vectors and matrices should be printed in
boldface italic type, e.g., B, b. Symbols for units should be printed in Roman type and should remain unaltered
in the plural, and should not be followed by a full stop except at the end of a sentence. References: International
Union of Pure and Applied Chemistry, Quantities, Units and Symbols in Physical Chemistry, Blackwell, Oxford,
1988; “Manual of Symbols and Terminology for Physicochemical Quantities and Units,” Pure Applied Chem.
31:577–638 (1972), 37:499–516 (1974), 46:71–90 (1976), 51:1–41, 1213–1218 (1979); 53:753–771 (1981),
54:1239–1250 (1982), 55:931–941 (1983); IUPAP-SUN, “Symbols, Units and Nomenclature in Physics,” Physica
93A: 1–60 (1978).
A. Atoms and molecules
Name Symbol SI unit Definition
Activity (radioactivity) A Bq A dN B /dt
Atomic mass constant m u kg m u m a ( 12 C)/12
Bohr magneton B J·T 1 B eh/4m e
Bohr radius a 0 m a 0 2 0 h 2 /m e e 2
Decay (rate) constant s 1 A N B
Dissociation energy D, E d J
From ground state D 0 J
From the potential minimum D e J
Electric dipole moment of a molecule p, C·m E p p E
Electric field gradient q V·m 2 q
2 V/
Electric polarizability of a molecule C·m 2 ·V 1 p(induced) E
Electron affinity E ea J
Electron rest mass m e kg
Elementary charge, proton charge e C
Fine structure constant e 2 /2 0 hc
g factor
g