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, NH 4 - Hydrogen carbonate ion, HCO 3 Hydroxide ion, OH - - Nitrate ion, NO 3 Carbonate ion, CO 3 2- Sulfate ion, SO 4 2- Phosphate ion, PO 4 3- 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(NO 3 ) 2 and not Mg 2+ (NO 3 - ) 2 or Mg(NO 3 - ) 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 SrOH 2 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 Li 2 CO 3 and not (Li) 2 CO 3 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, CuSO 4 and lead chloride, PbCl 2 Rule 5. The valency of silver is always 1. The valency of zinc is always 2.
112 Cn Copernicium 9 F 19.00 Fluorine 17 Cl 35.45 Chlorine 35 Br 79.90 Bromine 53 I 126.9 Iodine 85 At Astatine 7 N 14.01 Nitrogen 15 P 30.97 Phosphorus 33 As 74.92 Arsenic 51 Sb 121.8 Antimony 83 Bi 209.0 Bismuth 5 B 10.81 Boron 13 Al 31 Ga 69.72 Gallium 49 In 114.8 Indium 81 Tl 204.4 Thallium 107 Bh Bohrium 108 Hs Hassium 109 Mt Meitnerium 110 Ds Darmstadtium 111 Rg Roentgenium 87 Fr Francium 88 Ra Radium 89 103 Actinoids 104 Rf Rutherfordium 105 Db Dubnium 106 Sg Seaborgium 1 H 1.008 Hydrogen KEY 2 He 4.003 Helium 3 Li 6.941 Lithium 4 Be 9.012 Beryllium Atomic Number Symbol Standard Atomic Weight Name 197.0 Gold 6 C 12.01 Carbon 8 O 16.00 Oxygen 10 Ne 20.18 Neon 11 Na 22.99 Sodium 12 Mg 24.31 Magnesium 14 Si 28.09 Silicon 16 S 32.07 Sulfur 18 Ar 39.95 Argon 19 K 39.10 Potassium 20 Ca 40.08 Calcium 21 Sc 44.96 Scandium 22 Ti 47.87 Titanium 23 V 50.94 Vanadium 24 Cr 52.00 Chromium 25 Mn 54.94 Manganese 26 Fe 55.85 Iron 27 Co 58.93 Cobalt 28 Ni 58.69 Nickel 29 Cu 63.55 Copper 30 Zn 65.38 Zinc 32 Ge 72.64 Germanium 34 Se 78.96 Selenium 36 Kr 83.80 Krypton 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 42 Mo 95.96 Molybdenum 43 Tc Technetium 44 Ru 101.1 Ruthenium 45 Rh 102.9 Rhodium 46 Pd 106.4 Palladium 47 Ag 107.9 Silver 48 Cd 112.4 Cadmium 50 Sn 118.7 Tin 52 Te 127.6 Tellurium 54 Xe 131.3 Xenon 55 Cs 132.9 Caesium 56 Ba 137.3 Barium 57 71 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 Osmium 77 Ir 192.2 Iridium 78 Pt 195.1 Platinum 79 Au 197.0 Gold 80 Hg 200.6 Mercury 82 Pb 207.2 Lead 84 Po Polonium 86 Rn Radon 79 Au The Combining Power or Valencies of the Transition Metals Vary The Combining Power or Valencies of the Elements of the Periodic Table 26.98 Aluminium
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 MgOH 2 1 silver nitrate 2 ammonium nitrate 3 zinc sulfate 4 aluminium 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 aluminium phosphate 16 sodium hydrogen carbonate 17 barium nitrate 18 iron(ii) hydroxide 19 zinc phosphate 20 aluminium carbonate 21 silver phosphate 22 aluminium sulfate 23 potassium sulfate 24 silver sulfate 25 magnesium nitrate
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 MgOH 2 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 aluminium 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 of Compounds with Polyatomic Groups Sheet 1- ANSWERS 1 silver nitrate AgNO 3 2 ammonium nitrate NH 4 NO 3 3 zinc sulfate ZnSO 4 4 aluminium hydroxide Al(OH) 3 5 sodium sulfate Na 2 SO 4 6 potassium carbonate K 2 CO 3 7 magnesium hydroxide Mg(OH) 2 8 calcium carbonate CaCO 3 9 potassium phosphate K 3 PO 4 10 sodium nitrate NaNO 3 11 potassium hydroxide KOH 12 magnesium phosphate Mg 3 (PO 4 ) 2 13 barium hydroxide Ba(OH) 2 14 ammonium sulfate (NH 4 ) 2 SO 4 15 aluminium phosphate AlPO 4 16 sodium hydrogen carbonate NaHCO 3 17 barium nitrate Ba(NO 3 ) 2 18 iron(ii) hydroxide Fe(OH) 2 19 zinc phosphate Zn 3 (PO 4 ) 2 20 aluminium carbonate Al 2 (CO 3 ) 3 21 silver phosphate Ag 3 PO 4 22 aluminium sulfate Al 2 (SO 4 ) 3 23 potassium sulfate K 2 SO 4 24 silver sulfate Ag 2 SO 4 25 magnesium nitrate Mg(NO 3 ) 2
Chemical Formula of Compounds with Polyatomic Groups Sheet 2 - ANSWERS 26 sodium hydroxide NaOH 27 barium phosphate Ba 3 (PO 4 ) 2 28 calcium sulfate CaSO 4 29 potassium hydrogen carbonate KHCO 3 30 copper nitrate Cu(NO 3 ) 2 31 calcium phosphate Ca 3 (PO 4 ) 2 32 sodium carbonate Na 2 CO 3 33 lead(ii) sulfate PbSO 4 34 silver hydroxide AgOH 35 calcium nitrate Ca(NO 3 ) 2 36 calcium hydroxide Ca(OH) 2 37 sodium phosphate Na 3 PO 4 38 ammonium phosphate (NH 4 ) 3 PO 4 39 aluminium nitrate Al(NO 3 ) 3 40 barium sulfate BaSO 4 41 magnesium sulfate MgSO 4 42 iron(ii) sulfate FeSO 4 43 iron(iii) hydroxide Fe(OH) 3 44 lead(ii) nitrate Pb(NO 3 ) 2 45 copper sulfate CuSO 4 46 barium carbonate BaCO 3 47 copper hydroxide Cu(OH) 2 48 copper carbonate CuCO 3 49 zinc nitrate Zn(NO 3 ) 2 50 potassium nitrate KNO 3