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

Ammonium ion, NH4+

Carbonate ion, CO32-

Hydrogen carbonate ion, HCO3-

Sulfate ion, SO42-

Combining power of 3 Phosphate ion, PO43-

Hydroxide ion, OHNitrate ion, NO3Chemical 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. “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

1 H 1.008

KEY

Hydrogen

3 Li 6.941

4 Be 9.012

Lithium

Beryllium

11 Na 22.99

12 Mg 24.31

Atomic Number Symbol Standard Atomic Weight Name

Helium

5 B 10.81

79 Au 197.0 Gold

Boron

13 Al 26.98

The Combining Power or Valencies of the Transition Metals Vary

Sodium

Magnesium

19 K 39.10

20 Ca 40.08 Calcium

Scandium

Titanium

Vanadium

37 Rb 85.47

Rubidium

38 Sr 87.61

Strontium

39 Y 88.91 Yttrium

40 Zr 91.22

Zirconium

41 Nb 92.91

Niobium

Molybdenum

Technetium

Ruthenium

55 Cs 132.9

56 Ba 137.3

57–71

Cesium

Barium

Lanthanoids

72 Hf 178.5

Hafnium

73 Ta 180.9

Tantalum

74 W 183.9

Tungsten

75 Re 186.2

Rhenium

76 Os 190.2

87 Fr

88 Ra

89–103

104 Rf

105 Db

106 Sg

107 Bh

Francium

Radium

Actinoids

Rutherfordium

Dubnium

Seaborgium

Bohrium

Potassium

2 He 4.003

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

21 Sc 44.96

22 Ti 47.87

23 V 50.94

Carbon

7 N 14.01

Nitrogen

8 O 16.00

9 F 19.00

10 Ne 20.18

14 Si 28.09

15 P 30.97

16 S 32.07 Sulfur

17 Cl 35.45

Chlorine

18 Ar 39.95

34 Se 78.96

35 Br 79.90

36 Kr 83.80

Oxygen

Fluorine

Neon

Aluminum

Silicon

Phosphorus

32 Ge 72.64

33 As 74.92 Arsenic

Selenium

Bromine

51 Sb 121.8

52 Te 127.6

53 I 126.9

54 Xe 131.3

Argon

Chromium

25 Mn 54.94

Manganese

26 Fe 55.85

27 Co 58.93

28 Ni 58.69

29 Cu 63.55

30 Zn 65.38

31 Ga 69.72 Gallium

Germanium

42 Mo 95.96

43 Tc

44 Ru 101.1

45 Rh 102.9

Rhodium

46 Pd 106.4

Palladium

47 Ag 107.9 Silver

48 Cd 112.4

Cadmium

49 In 114.8

50 Sn 118.7 Tin

Antimony

Tellurium

77 Ir 192.2

80 Hg 200.6

81 Tl 204.4

82 Pb 207.2

83 Bi 209.0

85 At

86 Rn

Platinum

79 Au 197.0

84 Po

Iridium

78 Pt 195.1

Polonium

Astatine

Radon

108 Hs

109 Mt

110 Ds

111 Rg

112 Cn

Hassium

Meitnerium

24 Cr 52.00

Mg(OH)2 Al2(SO4)3

6 C 12.01

Iron

Osmium

Cobalt

Nickel

Copper

Gold

Darmstadtium Roentgenium

Zinc

Mercury

Indium

Thallium

Lead

Bismuth

Iodine

Krypton

Xenon

Copernicium

NH4Cl

Na2SO4

MgCO3

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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 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

Chemical formula

“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

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

Chemical formula

“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



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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



“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