NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
While there are many thousands of different chemical compounds there is a very definite system of nomenclature whereby we can name or write chemical formulas for most compounds. We divide the compounds into two main types – binary compounds and ternary compounds.
I. Binary Compounds All true binary compounds contain only two elements. The name of every binary compound ends with “ide.” Binary compounds come in three types. They are: Type I ………. the metal forms only one type of cation Type II ……… the metal forms two or more types of cations Type III …….. contains only nonmetals We will look at each type, one at a time.
Type I Binary Compounds For Type I binary compounds the metal present can be found in either Group 1 or Group 2 on the periodic table. The naming system for this type of compound is quite simple and is found below.
Rules for naming Type I binary compounds 1. The cation is always name first and the anion second. 2. A simple cation (obtained from a single atom) takes its name from the name of the element. 3. A simple anion (obtained from a single atom) is named by taking the first part of the element name (the root) and adding the letters “IDE.” 4. Write the name for the compound by combining the names of the ions.
When naming Type I binary compounds:
name of first element root + ide
The root is merely an abbreviation for the name of the second element. The roots of the most commonly used elements are listed in the following table.
Roots of the most commonly used elements.
arsenic = arsen nitrogen = nitr bromine = brom oxygen = ox carbon = carb phosphorus = phosph chlorine = chlor selenium = selen fluorine = fluor sulfur = sulf hydrogen = hydr tellurium = tellur iodine = iod
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Examples: Name the compound RbI. Rb is the chemical symbol for rubidium. I is the chemical symbol for iodine, whose root is “iod.” Add the “ide” ending to get iodide. Put the pieces together to get the name rubidium iodide.
Name the compound CaO. Ca is the chemical symbol for calcium. O is the symbol for oxygen, whose root is “ox.” Add the “ide” ending to get oxide. Put the pieces together to get the name calcium oxide.
Name the compound Li3N. Li is the chemical symbol for lithium. N is the chemical symbol for nitrogen, whose root is “nitr.” Add the “ide” ending to get nitride. Put the pieces together to get the name lithium nitride.
Write the formula for potassium sulfide. st The chemical symbol of potassium is K. K is in the 1 column of the periodic table, therefore, its ionic charge is +1. Sulfide is derived from sulfur, whose symbol is S. Its ionic charge is -2. +1 -2 So far we have… K S. The total positive charge must balance the total negative charge. Therefore, we need 2 K atoms to give a total positive charge of +2. This balances the -2 charge on the sulfur. Putting it all together we have K2S.
Write the formula for magnesium chloride. nd The chemical symbol of magnesium is Mg. Mg is in the 2 column of the periodic table, therefore, its ionic charge is +2. Chloride is derived from chlorine, whose symbol is Cl. Its ionic charge is -1. +2 -1 So far we have… Mg Cl The total positive charge must balance the total negative charge. Therefore, we need 2 chlorine atoms to give a total negative charge of -2. This balances the charge on the magnesium. Putting it all together we have MgCl2.
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Type II Binary Compounds For Type II binary compounds the metal present is NOT found in either Group 1 or Group 2 on the periodic table. The naming system for this type of compound is found below.
Rules for naming Type II binary compounds 1. The cation is always named first and the anion second. 2. A simple cation (obtained from a single atom) takes its name from the name of the element. Include a Roman numeral to indicate the ionic charge on the metal cation. 3. A simple anion (obtained from a single atom) is named by taking the first part of the element name (the root) and adding the letters “IDE.” 4. Write the name for the compound by combining the names of the ions.
When naming Type II binary compounds:
name of first element (Roman numeral) root + ide
Roman Numerals 1...... I 6 VI 2...... II 7...... VII 3...... III 8...... VIII 4...... IV 9...... IX 5...... V 10...... X
Examples: Name the compound FeCl2. Fe is the chemical symbol for iron. o Fe is not in Group 1 or Group 2; therefore a Roman numeral is needed in the name. We’ll come back to that shortly. Cl is the chemical symbol for chlorine, whose root is “chlor.” Add the “ide” ending to get chloride. At this point we have iron (??) chloride. To find the Roman numeral … o Find the charge of the anion. . Cl has a -1 charge. o Multiply times the number of those atoms to get the total negative charge. . There are 2 Cl atoms. . 2 times -1 = -2. total negative charge. o Balance total negative charge with total positive charge. . The total negative charge of -2 must be balanced with a total positive charge of +2. o Divide the total positive charge by the number of atoms to get Roman numeral. . There is only 1 Fe . +2 divided by 1 = +2. The Roman numeral is II. Put the pieces together to get the name iron (II) chloride.
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Name the compound PbS2. Pb is the chemical symbol for lead. o Pb is not in the Group 1 or Group 2; therefore a Roman numeral is needed. S is sulfur, whose root is “sulf.” Add the “ide” ending to get sulfide. At this point we have lead (??) sulfide. To find the Roman numeral … . S has a charge of -2. . There are 2 sulfur atoms so … 2 x -2 = -4. total negative charge . The total positive charge must be +4. . There is 1 lead atom so … +4 ÷ 1 = +4. The Roman numeral is IV. Put the pieces together to get the name lead (IV) sulfide.
Write the formula for nickel (III) oxide. The chemical symbol of nickel is Ni. The ionic charge is +3, as given by the Roman numeral. Oxide is derived from oxygen, whose symbol is O. Its ionic charge is -2. +3 -2 So far we have Ni O. In order to balance the charges we find the least common multiple (LCM) of 3 and 2. The LCM is 6. We need two Ni atoms (+6 ÷ +3 = 2) and three O atoms (-6 ÷ -2 = 3) to balance the charges. Putting it all together we have Ni2O3.
Write the formula for lead (IV) nitride. The chemical symbol of lead is Pb. The ionic charge is +4. Nitride is derived from nitrogen, whose symbol is N. Its ionic charge is -3. +4 -3 So far we have Pb N. The LCM of 4 and 3 is 12. We need three Pb atoms (+12 ÷ +4 = 3) and 4 N atoms (-12 ÷ -3 = 4) to balance the charges. Putting it all together we have Pb3N4.
Write the name for iron (II) oxide. The chemical symbol of iron is Fe. The ionic charge is +2. Oxide is derived from oxygen, whose symbol is O. Its ionic charge is -2. +2 -2 So far we have Fe O Since the charges already balance there is no additional work to be done. Putting it all together we have FeO.
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Type III Binary Compounds Type III binary compounds contain no metal atoms. The naming system for Type III compounds uses prefixes to indicate the number of each atom present. The naming system for this type of compound is found below.
Rules for naming Type III binary compounds 1. The first element in the formula is named first, and the full element name is used. 2. The second element is named as though it were an anion: root + ide. 3. Prefixes are used to denote the numbers of atoms present. (See table below) 4. The prefix mono- is never used for naming the first element.
When naming Type III binary compounds:
prefix + name of first element prefix + root + ide
Prefixes 1...... mono 6...... hexa 2...... di 7...... hepta 3...... tri 8...... octa 4...... tetra 9...... nona 5...... penta 10...... deca
Examples: Name the compound NO2. N is the chemical symbol of nitrogen. Since there is only one nitrogen atom AND it is the first element the prefix mono is not used. O is the chemical symbol of oxygen, whose root is ox. Add the -ide ending to get oxide. There are two oxygen atoms so we also add the prefix di to get dioxide. Put the pieces together to get the name nitrogen dioxide.
Name the compound N2O. N is the chemical symbol of nitrogen. Since there are two nitrogen atoms we need to add the prefix di to get dinitrogen. O is the chemical symbol of oxygen, whose root is ox. Add the -ide ending to get oxide. There is only one oxygen atom we add the prefix mono (mono IS used for the second element) to get monoxide. Put the pieces together to get the name dinitrogen monoxide.
Write the formula for carbon tetrachloride. The chemical symbol of carbon is C. There is no prefix before carbon in the chemical name, therefore, there is only 1 C atom in the chemical formula. Tetrachloride has the prefix tetra which means there are 4 atoms present. Chloride is derived from chlorine, whose symbol is Cl. Thus, there are 4 Cl atoms in the chemical formula. Putting it all together we have CCl4.
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Write the formula for dinotrogen pentaoxide. The prefix di means 2. Thus there are 2 N atoms in the chemical formula. The prefix penta means 5. Thus, there are 5 O atoms in the chemical formula. Putting it all together we have N2O5.
II. Ternary compounds Ternary compounds are easy to spot. They usually contain three different elements but may contain more. A ternary compound contains a polyatomic ion. A polyatomic ion is made up of two or more atoms that act as a single unit and have an electric charge.
Nearly all polyatomic ions have a negative charge which means they will be at the end of the + chemical formula and name. One notable exception is the ammonium ion (NH4 ). MEMORIZE THIS ION.
The names of nearly all polyatomic ions end with the letters –ate or –ite. Beware three - - 2- exceptions: cyanide (CN ), hydroxide (OH ), and peroxide (O2 ). These ions end with “ide” which can trick into thinking you have a binary compound when you actually have a ternary compound.
The naming system for ternary compounds is much the same as that for Type I and Type II binary compounds. The main difference is that you do not change the name of a polyatomic ion.
When naming compounds whose first member is a polyatomic ion use the following system:
name of polyatomic ion root + ide
Examples: Name the compound NH4Cl. + NH4 is ammonium o No Roman numeral is needed because ammonium always has a charge of +1. Cl is chlorine, whose root is chlor. Add the “ide” ending to get chloride. Answer…ammonium chloride
Write the formula for ammonium sulfide. + Ammonium is NH4 . Charge …+1. Sulfide is S. Charge …-2 +1 -2 So far we have NH4 S. Balance the charges to get (NH4)2S.
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When naming compounds whose second member is a polyatomic ion use the following system:
name of first element (R.N.?) name of polyatomic ion
Examples: Name the compound Na2SO4. Na is the symbol for sodium o Sodium is in Group 1 so no Roman numeral is needed. 2- SO4 is the formula of the sulfate ion. Put the pieces together to get the name sodium sulfate.
Name the compound CrPO4. Cr is the chemical symbol for chromium. o Cr is not in Group 1 or Group 2; therefore, a Roman numeral is needed. 3- PO4 is the formula of the phosphate ion. So far we have chromium (??) phosphate. To find the Roman numeral o The phosphate ion has a charge of -3. o There is only one phosphate ion so the total negative charge is -3. o The total positive charge must be +3 to balance the total negative charge. o Since there is only one chromium atom it gets the entire +3 charge. The Roman numeral is III. Putting it all together we have chromium (III) phosphate.
Write the formula for potassium cyanide. The chemical symbol of potassium is K. The absence of a Roman numeral indicates that potassium can be found in either Group 1 or Group 2. Its ionic charge is +1. The formula for the cyanide ion is CN- and its charge is -1. +1 -1 So far we have K CN. The charges already balance so the formula is KCN.
Write the formula for iron (III) chromate. Iron is Fe. The Roman numeral indicates a charge of +3. 2- Chromate is CrO4 . Its charge is -2. +3 -2 So far we have Fe CrO4. In order to balance the charges we need two iron atoms and three chromate ions. Putting it together we have Fe2(CrO4)3.
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When naming compounds composed of two polyatomic ions use the following system:
name of polyatomic ion name of polyatomic ion
Examples: Name the compound NH4CN. + NH4 is ammonium CN- is cyanide Answer … ammonium cyanide
Write the formula for ammonium sulfate. + Ammonium is NH4 . -2 Sulfate is SO4 . Answer … (NH4)2SO4.
III. Naming Polyatomic Ions That Contain Oxygen There are many atoms that form several different polyatomic ions with oxygen. The naming system for these ions is based on two things: the most common ion in each series and the number of oxygen atoms compared to the most common ion. The ones that concern us most are the ions of phosphorus, sulfur, nitrogen, chlorine and carbon. MEMORIZE THESE IONS IMMEDIATELY! 2- CO3 = carbonate - ClO3 = chlorate - NO3 = nitrate 3- PO4 = phosphate 2- SO4 = sulfate
When naming oxygen containing polyatomic ions:
One more oxygen than the most common ...... per ___ ate Most common ...... ___ ate One less oxygen than the most common ...... ___ ite Two less oxygen than the most common ...... hypo ___ ite
Examples: 3- PO5 = perphosphate 3- PO4 = phosphate (most common) 3- PO3 = phosphite 3- PO2 = hypophosphite
2- SO5 = persulfate 2- SO4 = sulfate (most common) (Note: Some of these ions do not exist in the 2- SO3 = sulfite real world. They are written here to show 2- SO2 = hyposulfite how to use the naming system.)
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IV. Naming Acids For this class, all acids begin with H (hydrogen). The names of all acids end with the word “acid.” There are two types of acids: those that contain oxygen and those that do not.
Naming acids that DO NOT contain oxygen 1. Take the name of the anion, add the prefix “hydro” and change the ending to “ic.” 2. Add the word “acid.”
When naming acids that DO NOT contain oxygen:
hydro + root of second element + ic acid
Examples: Name the compound HF. We know this is an acid because the chemical formula starts with “H.” Take the name of the anion (fluoride) add the prefix “hydro” and change the ending to “ic”: hydrofluoric Finally, add the word “acid.” hydrofluoric acid
Name the compound HCN. We know this is an acid because the chemical formula starts with “H.” There is no oxygen present so we start with the prefix “hydro.” Next, take the name of the anion (cyanide) and change the ending to “ic”: hydrocyanic Finally, add the word “acid.” hydrocyanic acid
Write the formula for hydrobromic acid. We know the formula starts with “H” because it is an acid. The charge on H is +1. We also know that the acid does not contain oxygen because of the “hydro” prefix. Removing the “hydro” and “ic” leaves us with “brom”, the root of bromine or Br. The charge on bromine is -1. +1 -1 So far we have H Br Balance the charges to get the formula HBr.
Write the formula for hydrosulfuric acid. We know the formula starts with “H” because it is an acid. The charge on H is +1. We also know that the acid does not contain oxygen because of the “hydro” prefix. Removing the “hydro” and “ic” leaves us with sulfur. The charge on sulfur is -2. +1 -2 So far we have H S Balance the charges to get the formula H2S.
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Naming Acids that DO contain oxygen 1. Find the name of the polyatomic ion. 2. Change “ate” to “ic” or “ite” to “ous.” 3. Add the word acid.
When naming acids that DO contain oxygen:
name of polyatomic ion root + ic/ous acid
(Change “ate” to “ic” or “ite” to “ous”)
Examples: Name the compound HClO4. We know this is an acid because it starts with “H.” - ClO4 is the perchlorate ion. Change the “ate” to “ic” and get perchloric. Add the word acid and get perchloric acid.
Name the compound H2SO3. We know this is an acid because it starts with “H.” 2- SO3 is the sulfite ion. Change the “ite” to “ous” and get sulfous. Add the word acid and get sulfous acid. o The name is actually sulfurous acid, which differs from the root for sulfur.
Write the formula for phosphorous acid. The word acid tells us the first element is “H.” The charge on H is +1. We also know it is a ternary acid because the prefix “hydro” (meaning binary acid) is missing. 3- Change “ous” to “ite” to get phosphite. The formula for phosphite is PO3 . Putting it together and balancing the charges we get H3PO3.
Write the formula for carbonic acid. The name tells us the first element is “H.” The charge on H is +1. We also know it is a ternary acid because the prefix “hydro” (meaning binary acid) is missing. 2- Change “ic” to “ate” to get carbonate. The formula for carbonate is CO3 . Putting it together and balancing charges we get H2CO3.
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Common Polyatomic Ions
Formula Name
1+ NH4 ammonium
1- C2H3O2 acetate 2- CO3 carbonate 1- HCO3 hydrogen carbonate or bicarbonate ClO1- hypochlorite 1- ClO2 chlorite 1- ClO3 chlorate 1- ClO4 perchlorate 2- CrO4 chromate 2- Cr2O7 dichromate CN1- cyanide OCN1- cyanate SCN1- thiocyanate OH1- hydroxide 1- NO2 nitrite 1- NO3 nitrate 1- MnO4 permanganate 3- PO4 phosphate 2- HPO4 hydrogen phosphate 1- H2PO4 dihydrogen phosphate 2- SO3 sulfite 2- SO4 sulfate 1- HSO4 hydrogen sulfate or bisulfate 2- S2O3 thiosulfate 3- AsO3 arsenite 3- AsO4 arsenate 2- C2O4 oxalate 2- O2 peroxide
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Assignment
Name each of the following compounds.
1. MnO 26. Cu(OH)2
2. ZnBr2 27. PCl5
3. Ca(ClO3)2 28. LiNO3
4. BaSO4 29. KH2PO4
5. AgNO3 30. CuCN
6. H2S 31. KHCO3
7. CaO 32. NaHSO4
8. H2CO3 33. Li2S2O3
9. Mg3(PO4)2 34. H3PO4
10. K2CrO4 35. MgSO4
11. NaI 36. Ca3(AsO3)2
12. Al(NO2)3 37. SiO2 13. ZnSe 38. CuCl
14. Sn(MnO4)2 39. KClO4
15. ICl5 40. CdSO3
16. CoSO3 41. NaBr
17. HF 42. P2O3
18. Fe2(SO4)3 43. HClO
19. Sn(Cr2O7)2 44. N2O4
20. AsBr3 45. NaH
21. KCN 46. WN2
22. NH4OH 47. PbC2O4
23. Fe(ClO4)3 48. H2Se
24. HNO2 49. H3PO2
25. CS2 50. CaH2
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Write the formula for each of the following compounds.
51. tin (II) nitrate 76. calcium bicarbonate 52. zinc phosphate 77. magnesium hydroxide 53. hypophosphorous acid 78. zinc bisulfate 54. iron (III) chloride 79. mercury (I) oxide 55. lithium sulfide 80. chlorous acid 56. silver oxalate 81. lead (IV) sulfide 57. perchloric acid 82. calcium acetate 58. potassium permanganate 83. sodium phosphate 59. strontium hypochlorite 84. gold (III) oxide 60. copper (I) sulfite 85. phosphorous acid 61. carbon disulfide 86. hydroiodic acid 62. calcium oxide 87. sodium fluoride 63. barium carbonate 88. diarsenic pentoxide 64. antimony (III) dichromate 89. sulfur dibromide 65. silicon dioxide 90. aluminum sulfate 66. iron (II) carbonate 91. dinitrogen trisulfide 67. sodium cyanide 92. nickel (III) iodide 68. carbon tetrafluoride 93. scandium (III) phosphate 69. cesium iodide 94. platinum (II) perchlorate 70. sodium chromate 95. sodium dihydrogen phosphate 71. hydrosulfuric acid 96. sulfurous acid 72. aluminum oxide 97. strontium carbonate 73. ammonium thiocyanate 98. copper (II) hydroxide 74. boron trifluoride 99. bismuth (III) oxalate 75. radium sulfate 100. diphosphorous pentaselenide
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