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Writing Chemical formula with polyatomic groups

1. Use the Periodic table to determine the combining powers of single elements. Eg. Magnesium is in Group 2 and has a combining power of 2.

2. Use Table 1 to determine the valency of the major polyatomic groups.

Table 1: The Combining Power of Polyatomic Ions

Combining power of 1 Combining power of 2 Combining power of 3

Ammonium ion, NH4+

Hydrogen carbonate ion, HCO3-

Hydroxide ion, OH-

Nitrate ion, NO3-

Carbonate ion, CO32-

Sulfate ion, SO42-

Phosphate ion, PO43-

Chemical Formula Help

Rule 1: The charge tells you the combining power. Do not write the charge in the chemical formula!

Eg. The chemical formula for magnesium nitrate is Mg(NO3)2 and not Mg2+(NO3-)2 or Mg(NO3

-)2

Rule 2: Brackets() are needed when a polyatomic group > 1 in a compound. Poly = ‘many’

The hydroxide ion, formula OH-, is a polyatomic group since it is made up of two different elements.

Eg. The chemical formula for strontium hydroxide is Sr(OH)2 and not SrOH2

Eg. The formula for lithium hydroxide is LiOH and not Li(OH) since there is only one OH group.

Rule 3: Do not use brackets when single elements are > 1 in a formula.

Eg. The chemical formula for lithium carbonate is Li2CO3 and not (Li)2CO3

Rule 4. Roman numerals are used for metal valencies that vary. Eg. Iron(II) oxide, FeO

If in doubt use a combining power of 2. Eg. Copper sulfate, CuSO4 and lead chloride, PbCl2

Rule 5. The valency of silver is always 1. The valency of zinc is always 2.

112Cn

Copernicium

9F

19.00Fluorine

17Cl

35.45Chlorine

35Br

79.90Bromine

53I

126.9Iodine

85At

Astatine

7N

14.01Nitrogen

15P

30.97Phosphorus

33As

74.92Arsenic

51Sb

121.8Antimony

83Bi

209.0Bismuth

5B

10.81Boron

13Al

31Ga

69.72Gallium

49In

114.8Indium

81Tl

204.4Thallium

107Bh

Bohrium

108Hs

Hassium

109Mt

Meitnerium

110Ds

Darmstadtium

111Rg

Roentgenium

87Fr

Francium

88Ra

Radium

89–103

Actinoids

104Rf

Rutherfordium

105Db

Dubnium

106Sg

Seaborgium

1H

1.008Hydrogen KEY

2He

4.003Helium

3Li

6.941Lithium

4Be

9.012Beryllium

Atomic Number

Symbol

Standard Atomic WeightName

197.0Gold

6C

12.01Carbon

8O

16.00Oxygen

10Ne

20.18Neon

11Na

22.99Sodium

12Mg

24.31Magnesium

14Si

28.09Silicon

16S

32.07Sulfur

18Ar

39.95Argon

19K

39.10Potassium

20Ca

40.08Calcium

21Sc

44.96Scandium

22Ti

47.87Titanium

23V

50.94Vanadium

24Cr

52.00Chromium

25Mn

54.94Manganese

26Fe

55.85Iron

27Co

58.93Cobalt

28Ni

58.69Nickel

29Cu

63.55Copper

30Zn

65.38Zinc

32Ge

72.64Germanium

34Se

78.96Selenium

36Kr

83.80Krypton

37Rb

85.47Rubidium

38Sr

87.61Strontium

39Y

88.91Yttrium

40Zr

91.22Zirconium

41Nb

92.91Niobium

42Mo

95.96Molybdenum

43Tc

Technetium

44Ru

101.1Ruthenium

45Rh

102.9Rhodium

46Pd

106.4Palladium

47Ag

107.9Silver

48Cd

112.4Cadmium

50Sn

118.7Tin

52Te

127.6Tellurium

54Xe

131.3Xenon

55Cs

56Ba

137.3Barium

57–71

Lanthanoids

72Hf

178.5Hafnium

73Ta

180.9Tantalum

74W

183.9Tungsten

75Re

186.2Rhenium

76Os

190.2Osmium

77Ir

192.2Iridium

78Pt

195.1Platinum

79Au

197.0Gold

80Hg

200.6Mercury

82Pb

207.2Lead

84Po

Polonium

86Rn

Radon

79Au

The Combining Power or Valencies of the Transition Metals Vary

The Combining Power or Valencies of the Elements of the Periodic Table

132.9Cesium

26.98Aluminum

“Aluminum” is a commonly used spelling alternative spelling for “aluminium” that is used in the US May be freely copied for educational use. ©www.chemicalformula.org

Chemical Formula of Compounds with Polyatomic Groups – Sheet 1

A polyatomic group contains more than 1 element. Eg. The hydroxide group, OH- contains oxygen and hydrogen.

Polyatomic groups greater than 1 in a formula need brackets. eg. Mg(OH)2 and not MgOH2

No. Compound Chemical formula

1 silver nitrate

2 ammonium nitrate

3 zinc sulfate

4 aluminum hydroxide

5 sodium sulfate

6 potassium carbonate

7 magnesium hydroxide

8 calcium carbonate

9 potassium phosphate

10 sodium nitrate

11 potassium hydroxide

12 magnesium phosphate

13 barium hydroxide

14 ammonium sulfate

15 aluminum phosphate

16 sodium hydrogen carbonate

17 barium nitrate

18 iron(II) hydroxide

19 zinc phosphate

20 aluminum carbonate

21 silver phosphate

22 aluminum sulfate

23 potassium sulfate

24 silver sulfate

25 magnesium nitrate

“Aluminum” is a commonly used spelling alternative spelling for “aluminium” that is used in the US May be freely copied for educational use. ©www.chemicalformula.org

Chemical Formula of Compounds with Polyatomic Groups – Sheet 2

A polyatomic group contains more than 1 element. Eg. The hydroxide group, OH- contains oxygen and hydrogen.

Polyatomic groups greater than 1 in a formula need brackets. eg. Mg(OH)2 and not MgOH2

No. Compound Chemical formula

26 sodium hydroxide

27 barium phosphate

28 calcium sulfate

29 potassium hydrogen carbonate

30 copper nitrate

31 calcium phosphate

32 sodium carbonate

33 lead(II) sulfate

34 silver hydroxide

35 calcium nitrate

36 calcium hydroxide

37 sodium phosphate

38 ammonium phosphate

39 aluminum nitrate

40 barium sulfate

41 magnesium sulfate

42 iron(II) sulfate

43 iron(III) hydroxide

44 lead(II) nitrate

45 copper sulfate

46 barium carbonate

47 copper hydroxide

48 copper carbonate

49 zinc nitrate

50 potassium nitrate

“Aluminum” is a commonly used spelling alternative spelling for “aluminium” that is used in the US May be freely copied for educational use. ©www.chemicalformula.org

Chemical Formula of Compounds with Polyatomic Groups – Sheet 1- ANSWERS

No. Compound Chemical formula

1 silver nitrate AgNO3

2 ammonium nitrate NH4NO3

3 zinc sulfate ZnSO4

4 aluminum hydroxide Al(OH)3

5 sodium sulfate Na2SO4

6 potassium carbonate K2CO3

7 magnesium hydroxide Mg(OH)2

8 calcium carbonate CaCO3

9 potassium phosphate K3PO4

10 sodium nitrate NaNO3

11 potassium hydroxide KOH

12 magnesium phosphate Mg3(PO4)2

13 barium hydroxide Ba(OH)2

14 ammonium sulfate (NH4)2SO4

15 aluminum phosphate AlPO4

16 sodium hydrogen carbonate NaHCO3

17 barium nitrate Ba(NO3)2

18 iron(II) hydroxide Fe(OH)2

19 zinc phosphate Zn3(PO4)2

20 aluminum carbonate Al2(CO3)3

21 silver phosphate Ag3PO4

22 aluminum sulfate Al2(SO4)3

23 potassium sulfate K2SO4

24 silver sulfate Ag2SO4

25 magnesium nitrate Mg(NO3)2

“Aluminum” is a commonly used spelling alternative spelling for “aluminium” that is used in the US May be freely copied for educational use. ©www.chemicalformula.org

Chemical Formula of Compounds with Polyatomic Groups – Sheet 2 - ANSWERS

No. Compound Chemical formula

26 sodium hydroxide NaOH

27 barium phosphate Ba3(PO4)2

28 calcium sulfate CaSO4

29 potassium hydrogen carbonate KHCO3

30 copper nitrate Cu(NO3)2

31 calcium phosphate Ca3(PO4)2

32 sodium carbonate Na2CO3

33 lead(II) sulfate PbSO4

34 silver hydroxide AgOH

35 calcium nitrate Ca(NO3)2

36 calcium hydroxide Ca(OH)2

37 sodium phosphate Na3PO4

38 ammonium phosphate (NH4)3PO4

39 aluminum nitrate Al(NO3)3

40 barium sulfate BaSO4

41 magnesium sulfate MgSO4

42 iron(II) sulfate FeSO4

43 iron(III) hydroxide Fe(OH)3

44 lead(II) nitrate Pb(NO3)2

45 copper sulfate CuSO4

46 barium carbonate BaCO3

47 copper hydroxide Cu(OH)2

48 copper carbonate CuCO3

49 zinc nitrate Zn(NO3)2

50 potassium nitrate KNO3