14 Science, mathematics, and computing

14.4 Chemistry

14.4.1 Introduction

The International Union of Pure and Applied Chemistry (IUPAC) generates comprehensive advice on chemical nomenclature, terminology, standardized methods for measurement, and atomic weights. By their recommendations, symbols for the elements are set in roman with an initial capital, no point at the end; spelled-out names of chemical compounds are in lower-case roman; and symbols for the elements in formulas are printed in roman without spaces:

H2SO4 Cu(CrO2)2
Table 14.3 lists the IUPAC-accepted names and abbreviations of chemical elements.

14.4.2 Roman and italic

In certain kinds of name, symbols are printed in italic (O-methylhydroxylamine, fac-triamine-trinitrosylcobalt(iii)). Italic is also used for certain prefixes, of which the commonest are o-, m-, p-, cis-, and trans- (o-tolidine, p-diethylbenzene, cis-but-2-ene). Retain the italic, but not

the cis isomer

position a is ortho to the methyl group

the hyphen, when the prefix is used as a separate word:

The prefixes d-, l-, and dl- are no longer used for labelling stereoisomers, which are expressed either by small capitals or by symbols: D-(+), L-(−), and DL-(±) respectively; for example ‘dl-lactic acid’, ‘(+)-tartaric acid’. In each case the hyphens must be retained, although not when expressing their absolute configuration.

14.4.3 Formulas and structural drawings

A chemical formula shows the elements present in a compound and their relative proportions (H2O, C2H6O); a chemical equation represents the changes that occur in a chemical reaction, in words or symbols:

glucose + oxygen→carbon dioxide + water

C6H12O6(aq) + O2(g)→CO2(g) + H2O(g)

Table 14.3 Chemical elements

Element

Symbol

Atomic no.

actinium

Ac

89

aluminium

Al

13

americium

Am

95

antimony

Sb

51

argon

Ar

18

arsenic

As

33

astatine

At

85

barium

Ba

56

berkelium

Bk

97

beryllium

Be

4

bismuth

Bi

83

bohrium

Bh

107

boron

B

5

bromine

Br

35

cadmium

Cd

48

caesium

Cs

55

calcium

Ca

20

californium

Cf

98

carbon

C

6

cerium

Ce

58

chlorine

Cl

17

chromium

Cr

24

cobalt

Co

27

copernicium

Cn

112

copper

Cu

29

curium

Cm

96

darmstadtium

Ds

110

dubnium

Db

105

dysprosium

Dy

66

einsteinium

Es

99

erbium

Er

68

europium

Eu

63

fermium

Fm

100

flerovium

Fl

114

fluorine

F

9

francium

Fr

87

gadolinium

Gd

64

gallium

Ga

31

germanium

Ge

32

gold

Au

79

hafnium

Hf

72

hassium

Hs

108

helium

He

2

holmium

Ho

67

hydrogen

H

1

indium

In

49

iodine

I

53

iridium

Ir

77

iron

Fe

26

krypton

Kr

36

lanthanum

La

57

lawrencium

Lr

103

lead

Pb

82

lithium

Li

3

livermorium

Lv

116

lutetium

Lu

71

magnesium

Mg

12

manganese

Mn

25

meitnerium

Mt

109

mendelevium

Md

101

mercury

Hg

80

molybdenum

Mo

42

neodymium

Nd

60

neon

Ne

10

neptunium

Np

93

nickel

Ni

28

niobium

Nb

41

nitrogen

N

7

nobelium

No

102

osmium

Os

76

oxygen

O

8

palladium

Pd

46

phosphorus

P

15

platinum

Pt

78

plutonium

Pu

94

polonium

Po

84

potassium

K

19

praseodymium

Pr

59

promethium

Pm

61

protactinium

Pa

91

radium

Ra

88

radon

Rn

86

rhenium

Re

75

rhodium

Rh

45

roentgenium

Rg

111

rubidium

Rb

37

ruthenium

Ru

44

rutherfordium

Rf

104

samarium

Sm

62

scandium

Sc

21

seaborgium

Sg

106

selenium

Se

34

silicon

Si

14

silver

Ag

47

sodium

Na

11

strontium

Sr

38

sulphur

S

16

tantalum

Ta

73

technetium

Tc

43

tellurium

Te

52

terbium

Tb

65

thallium

Tl

81

thorium

Th

90

thulium

Tm

69

tin

Sn

50

titanium

Ti

22

tungsten

W

74

uranium

U

92

vanadium

V

23

xenon

Xe

54

ytterbium

Yb

70

yttrium

Y

39

zinc

Zn

30

zirconium

Zr

40

Formulas and reaction schemes may be numbered separately from figures, often with a sequence of bold numbers or letters in square brackets or parentheses, ranged right.

When expressing formulas, the order of brackets normally follows that in mathematics: {[( )]}. Parentheses are used to define the extent of a chemical group, as in (C2H5)3N; square brackets are used to denote, for example, chemical concentration in complex formulas: [H2SO4]. This sequence will vary in certain circumstances, for example in the use of square brackets in denoting coordination compounds:

K3[Fe(CN)6]

[Ni(CO)4]

In organic chemical nomenclature, it is usual to write a formula as a series of groups (known as a structural formula):

CH3COC2H5

RCH2COOCH3

Medial dots can be used to divide off the groups, if clarification of a formula is needed (usually in textbooks). Unicode code point U+00B7 middle dot is acceptable.

(CH3CO·C2H5;

R·CH2·COOCH3)

In most other contexts they can be dispensed with, although dots are required in formulas of addition compounds (Na2CO3·10H2O). Indicate a single bond with a closed-up en rule or a minus sign (C–H), a double bond by an equals sign (CH3CH=CH2), and a triple bond by an equivalence sign (U+2261 identical to) (CH3C≡CH).

In chemical equations, different types of arrows are used to represent reactions or electron movement; arrows may be single or double barbed—each has significance. For example, a long double-barbed arrow is used to indicate the direction of a reaction

CO2 + 2H2O →CH4 + 2O2

and two single-barbed arrows pointing in opposite directions indicate a reversible reaction, which may be in balanced equilibrium (same length arrows)

N2 + 3H2 ⇌ 2NH3

or favour either the reactants or products (different length arrows).

Equations and displayed or skeletal formulas can be created in dedicated chemistry drawing packages; anything other than simple, single-line formulas that can be word processed will be treated as artwork (for details see Chapter 16). There are also TeX macro packages that can be used for creating chemistry graphics or typesetting chemistry according to a publisher’s style (see 14.6.1).

14.4.4 Superscripts and subscripts

Superscripts and subscripts need not occur only singly, and need not follow what they modify. In specifying a particular nuclide, the atomic (proton) number is printed as a left subscript (12Mg). Similarly, the mass (nucleon) number of an element is shown with its symbol and printed as a left superscript (235U, 14C)—not to the right, as formerly. If it is given with the name of the element no hyphen is necessary (uranium 235, carbon 14).

In inorganic chemical nomenclature the relationship between the superscripts and subscripts surrounding a chemical symbol is important: superscript expresses the electrical charge and subscript the number of atoms for each molecule. These should be staggered so as to indicate the ions present (Na+2CO32– (sodium carbonate) but Hg22+Cl2 (dimercury(I) chloride)). A medial dot is used to indicate coordinated species (CuSO4.5H2O). Ionic charge is shown by a right superscript (SO42–). Indicate complex ions by square brackets: K+3[FeCl6]3–.

Indicate oxidation states by a small-capital Roman numeral, set in parentheses close up to the spelled-out name, for example ‘manganese(iv)’; or by a superscript Roman numeral set in capitals to the right of the abbreviated name, for example ‘Mniv.

Atomic orbitals, designated s, p, d, f, g, are roman, and can have subscript letters with superscript numbers attached (dz2, dx2–dy2).


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