1. Chemistry 068, Chapter 5

2. Compounds and Nomenclature Most substances are compounds rather than elements. Compounds are substances formed from more than one element. Nomenclature is the system used to name chemical compounds.

3. Molecules Lone atoms are fairly rare – most matter is made up of multiple atoms acting together. A group of two or more atoms, tightly bonded together, that functions as a single unit is called a molecule. Aggregates of many molecules can be either ionic (held together by positive and negative charged atoms strongly held together in a lattice) or molecular (lots of molecules weakly held together).

4. Classifying Molecules Molecules can be homonuclear or heteronuclear. –Homonuclear, or homoatomic, molecules consist of only one type of atom. These can still be called elements. –Heteronuclear, or heteroatomic, molecules consist of more than one type of atom. These are compounds. The number of atoms in the molecule leads to the molecule being called diatomic (2 atoms), triatomic (3 atoms), tetratomic (4 atoms), and so forth.

5. Chemical Formulas A chemical formula is a representation of the number of and types of elements present in a compound. –It is very important to strictly follow the rules for writing chemical symbols in chemical formulas. –CO (one carbon and one oxygen) is not the same as Co (one cobalt). Subscripts on atoms indicate the number of atoms of each type in the molecule. –Atoms in parenthesis indicate sub-units in the molecules. A subscript on the parenthesis is multiplied times all of the atoms in the parenthesis to indicate the number of atoms.

6. Chemical Formulas (Cont’d) All portions of a compound will have this constant ratio of atoms. –This is the law of constant composition. The meaning of the chemical formula varies slightly between ionic and molecular compounds. –In ionic compounds, the formula gives the ratio of the atom in the compound. –In molecular compounds, the formula gives the ratio of the atoms in the individual molecules making up the compound.

7. Chemical Formula Problems How many of each type of atom are in each of the following compounds? –CO 2 –O 2 –(NH 4 ) 2 O

8. Chemical Formula Problems (Cont’d) Use the given information to write a formula for each of the following compounds. –Three carbons and eight hydrogens. –Two hydrogens and one oxygen. –One carbon and four hydrogens.

9. Types of Chemical Formulas An empirical formula gives the simplest whole number ratio of atoms. A molecular formula gives actual number of atoms in the molecule. For example CH is an empirical formula, C 6 H 6 is a molecular formula. A structural formula uses lines to show how a molecule is put together. (More on these is a later chapter).

10. Molecular View Elements can be split into two categories. –Atomic elements exist as single atoms. –Molecular elements do not normally exist in nature as single atoms. Compounds are typically either molecular or ionic. –Molecular compounds are formed by two or more nonmetals. –Ionic compounds are formed by metals and nonmetals or polyatomic ions bonding.

11. Predicting Ionic Charge It is possible to predict ionic charge from the position of an element on the periodic table. The first two groups will form positive ions equal to their group #. The charge on transition metals cannot be easily predicted. The charge on the last group (noble gasses) is zero. The next three groups will be -1 each group left of the noble gasses. The remaining two groups are harder to predict as they can be positive or negatively charged.

13. Predicting Ionic Charge Problems Predict the charge of ions formed from the following atoms. –Na –Al –P –Cl –Ar

14. Isoelectronic Species Isoelectronic species have the same number of electrons. This does NOT mean they have the same properties, they are only alike in the number of electrons they posses.

15. Ionic Compound Formulas Ionic compounds are molecules formed by combining two ions. –Either single or polyatomic ions. The cation is always listed first in the formula. The charges on individual ions is not shown. Formulas must have a net charge of zero. Ratios of the ions must create a zero net charge – you must have as many positive charges as negative charges. For example: – NaCl is formed from Na + and Cl - –CaBr 2 is formed from Ca 2+ and Br -

16. Typical Ionic Formulas Anions (X) Cation (M) --2-3-4 +MXM 2 XM 3 XM 4 X +2MX 2 MXM 3 X 2 M 2 X +3MX 3 M 2 X 3 MXM 4 X 3 +4MX 4 MX 2 M 3 X 4 MX

17. Ionic Compound Problems Determine the empirical formulas for the ionic compounds formed by combining the following: –Mg 2+ and F - –Fe 3+ and O 2- –Be 2+ and S 2-

18. Polyatomic Ions Polyatomic ions consist of a group of atoms, held together by covalent bonds, which are held together due to the loss or gain of electrons. The entire polyatomic group works the same way as a single ion when determining formulas. It is important to realize that polyatomic ions are not true molecules, they are pieces of compounds and not compounds themselves.

19. Ionic Compound Problems Determine the empirical formulas for the ionic compounds formed by combining the following: –Mg 2+ and OH - –NH 4 + and O 2- –Na + and NO 3 -

20. Nomenclature Nomenclature is the system used to name chemical compounds. –The system has been adopted by the IUPAC. There are separate rules for different types of molecules. Most of these rules apply to binary compounds. –Binary compounds are those consisting of only two elements.

21. Classification of Compounds for Nomenclature For nomenclature purposes, molecules are broken down into several categories: –Elements. –Ions and ionic compounds. For nomenclature purposes, and compound of a metal and nonmetal are considered ionic as are compounds containing one or more polyatomic ions. –Binary molecular compounds. Again, for nomenclature purposes, these only include compounds of nonmetals and nonmetals. Metalloids are usually named using molecular nomenclature. –Acids.

22. Nomenclature – Elements Naming elements is simple – you just use the name off of the periodic table. In the case of elements that normally exist as diatomic molecules, rather than single atoms, you still use the element name. –They are sometimes indicated as diatomic element or molecular element to differentiate them from a single atom. –This specifically applies to H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2

23. Nomenclature – Elements Examples Fe N 2 Sn

24. Binary Ionic Compounds Binary ionic compounds contain a metal and a nonmetal. Binary ionic compounds are contain either fixed charge or variable charge metal ions. –The naming rules are slightly different for each.

25. Fixed vs. Variable Charge Metal Ions Fixed charge metal ions can only have one possible charge. –There are only 15 fixed charge elements. –They are: Li +, Na +, K +, Rb +, Cs +, Ag +, Be 2+, Mg 2+, Ca 2+,Sr 2+,Ba 2+, Zn 2+, Cd 2+, Al 3+, Ga 3+. Variable charge metal ions can have different charges. –Each charge has a separate name, so Fe 2+ has a different name than Fe 3+. –All metals, other than the 15 above, are variable charge.

27. Positive Ion Nomenclature Positive ions are simply called metal ion, unless there is more than one possible positive ion (variable charged). Polyatomic ions each have their own name. Fixed charge metals are thus: –Note that the particular charge does not matter. –So Na + is called sodium ion. –Mg 2+ is called magnesium ion.

28. Positive Ion Nomenclature (Cont’d) In the case of variable charge metals they are named metal (charge) ion with the charge in roman numerals. –In this case, charge does matter, as you must denote which charge it has. –Cu + is thus copper (I) ion. –Cu 2+ is thus copper (II) ion. For variable charge metals, there is also an older method which uses ous suffix for smaller charge and ic for larger charge. –Cu + is thus cuprous ion. –Cu 2+ is thus cupric ion.

29. Common Variable Charge Metal Ions ElementIonsOld Root Name Chromium (Cr)+2, +3Chrom- Cobalt (Co)+2, +3Cobalt- Copper (Cu)+1, +2Cupr- Gold (Au)+1, +3Aur- Iron (Fe)+2, +3Ferr- Lead (Pb)+2, +4Plumb- Manganese (Mn)+2, +3Mangan- Tin (Sn)+2, +4Stann- Mercury (Hg)Hg 2 2+ ; Hg 2+ Mercur-

30. Negative Ion Nomenclature Polyatomic ions each have their own name. Single atom negative ions consist of a stem which denotes the particular ion and end in ide.

31. Common Negative Ions ElementIon Stem Name Bromine (Br)-1Brom- Carbon (C)-4Carb- Chlorine (Cl)-1Chlor- Fluorine (F)-1Fluor- Hydrogen (H)-1Hydr- Iodine (I)-1Iod- Nitrogen (N)-3Nitr- Oxygen (O)-2Ox- Phosphorous (P)-3Phosph- Sulfur (S)-2Sulf-

32. Ion Nomenclature Problems Name each of the following ions. Ag + Fe 2+ Fe 3+ Cl - O 2-

33. Ion Nomenclature Problems (Cont’d) Write formulas for each of the following ions. Bromide ion. Stannic ion. Manganese (III) ion. Hydrogen ion. Lithium ion.

34. Binary Ionic Compound Nomenclature Ionic compound names consist of two words. The first is the name of the metal. The word ion is excluded. –In the case of variable charge metals the charge is indicated by a roman numeral in parenthesis or by the old systematic names (-ic and –ous). The second is the name of the nonmetal ion, dropping the word ion. Note that the number of each ion is not a part of the name – it is inferred from the ions that form the compound. –Thus you must be able to determine the formula of an ionic compound from the name and the type of ions in it. Thus, NaCl is called sodium chloride. Thus, FeCl 2 is called iron (II) chloride or ferrous chloride.

35. Binary Ionic Compound Nomenclature Problems Name each of the following compounds. AgCl CaBr 2 FeO Fe 2 O 3 K 3 N

36. Binary Ionic Compound Nomenclature Problems (Cont’d) Write formulas for each of the following compounds. Potassium bromide. Stannic chloride. Manganese (III) nitride. Sodium carbide. Silver fluoride.

37. Nomenclature of Polyatomic Ions There are hundreds of polyatomic ions and each one has its own name. There is no easy way to learn the polyatomic ions. –Memorization is required. –There are very few patterns. The halogens follow the same names and charges. –The only thing that changes is the halogen stem name. There is a general pattern for the oxygen containing ions: –Lowest # Oxygens to greatest follows: –One to four oxygens: hypo-ite, -ite, -ate, per-ate –Only two possible: -ite, -ate Thio- compounds replace an oxygen with a sulfur. –OCN - is cyanate ion, SCN - is thiocyanate.

38. Common Polyatomic Ions ElementFormulaName NitrogenNO 3 - Nitrate ion NO 2 - Nitrite ion NH 4 + Ammonium ion N 3 - Azide ion SulfurSO 4 2- Sulfate ion HSO 4 - Hydrogen sulfate ion (bisulfate ion) SO 3 2- Sulfite ion HSO 3 - Hydrogen sulfite ion (bisulfite ion) S 2 O 3 2- Thiosulfate ion PhosphorusPO 4 3- Phosphate ion HPO 4 2- Hydrogen phosphate ion H 2 PO 4 - Dihydrogen phosphate ion PO 3 3- Phosphite ion

39. Common Polyatomic Ions (Cont’d) ElementFormulaName CarbonCO 3 2- Carbonate ion HCO 3 - Hydrogen carbonate ion (bicarbonate ion) C 2 O 4 2- Oxalate ion *C 2 H 3 O 2 - Acetate ion CN - Cyanide ion OCN - Cyanate ion SCN - Thiocyanate ion Chlorine**ClO 4 - Perchlorate ion ClO 3 - Chlorate ion ClO 2 - Chlorite ion ClO - Hypochlorite ion *Sometimes written CH 3 COO - **All of the halogens follow the same pattern.

40. Common Polyatomic Ions (Cont’d) ElementFormulaName OxygenO 2 2- Peroxide ion BoronBO 3 3- Borate ion HydrogenH 3 O + Hydronium ion OH - Hydroxide ion MetalsMnO 4 - Permanganate ion CrO 4 2- Chromate ion Cr 2 O 7 2- Dichromate ion

41. Nomenclature of Polyatomic Ions Problems Name each of the following ions. OH - SO 4 2- SO 3 2- NO 3 - NH 4 +

42. Nomenclature of Polyatomic Ions Problems (Cont’d) Write formulas for each of the following ions. Hydronium ion. Permanganate ion. Perchlorate ion. Peroxide ion. Acetate ion.

43. Nomenclature of Polyatomic Ion Containing Compounds Follow the same rules as binary ionic compound nomenclature. Names consist of two words. The first is the name of the positive ion, dropping the word ion. The second is the name of the negative ion, dropping the word ion. Again, the numbers of each ion is not a part of the name. Thus, NaOH is called sodium hydroxide. Thus, Fe(ClO) 2 is called iron (II) hypochlorite or ferrous hypochlorite.

44. Nomenclature of Polyatomic Ion Containing Compounds Problems Name each of the following compounds. KOH Li 3 PO 4 Na 2 SO 4 NH 4 ClO 3 NaNO 3

45. Nomenclature of Polyatomic Ion Containing Compounds Problems (Cont’d) Write formulas for each of the following compounds. Sodium peroxide. Stannic borate. Chromium (III) Phosphate. Sodium carbonate. Lithium hydrogen sulfate. Auric oxalate.

46. Nomenclature of Binary Molecular (Covalent) Compounds Binary covalent compounds consist of two types of nonmetal atoms. Greek prefixes are used to indicate the number of each type of atom.

47. Nomenclature of Binary Molecular (Covalent) Compounds (Cont’d) Greek Prefixes # AtomsPrefix 1mono- 2di- 3tri- 4tetra- 5penta- 6hexa- 7hepta- 8octa- 9nona- 10deca-

48. Nomenclature of Binary Molecular (Covalent) Compounds (Cont’d) The order of which atom is first follows the following pattern. –The element further to the left is central. B  Si/C  Sb/As/P/N  H  Te/Se/S  I/Br/Cl  O  F The central atom is usually, but not always, listed first in its formula and name. –The central atom is usually the least electronegative.

49. Nomenclature of Binary Molecular (Covalent) Compounds (Cont’d) Names consist of two words. This first is prefixnonmetal. The second prefixnonmetalide. –The second element is given the name of its negative ion (the –ide ending). The mono prefix is dropped for the first nonmetal. –Any other prefix is kept. –Mono is kept for the second element. Thus, BBr 3 is boron tribromide. Thus B 2 Br 6 is Diboron hexabromide.

50. Nomenclature of Binary Molecular (Covalent) Compound Problems (Cont’d) Name each of the following compounds. CO CO 2 H 2 O ClO 2 NO 2

51. Nomenclature of Binary Molecular (Covalent) Compound Problems (Cont’d) Write formulas for each of the following compounds. Silicon dioxide. Nitrogen dioxide. Sulfur trioxide. Tetrasulfur tetranitride. Carbon tetrahydride.

52. Nomenclature of Acids For nomenclature purposes, acids are hydrogen containing compounds whose molecules yield H + ion in water. –Note that we only use this definition for nomenclature purposes. To be considered an acid for nomenclature purposes it must contain only hydrogen and negative ions. Not all compounds that contain hydrogen are acids. –Acids are noted by listing hydrogen as the first element in the formula. –Of note as an exception is water, H 2 O.

53. Nomenclature of Acids (Cont’d) The naming for acids depends on weather or not the acid is in water. Acids in water are denoted by (aq) appearing next to the name. –For example, HCl(aq) If an acid is NOT in water, it follows the normal rules for (covalent) molecular compound nomenclature. If an acid is in water, it follows the naming rules for acids that follow.

54. Nomenclature of Acids (Cont’d) Acid naming follows the rules for ionic compound naming with the following differences. Front hydrogens are not included in the name. The word acid is added to the end of all names. Naming is based upon negative ion (anion) naming which is then modified. When writing the formulas from names, enough hydrogens (+1 each) are added to the negative ion to produce a neutral (uncharged) molecule.

55. Nomenclature of Acids (Cont’d) Anion suffixes are replaced with acidic suffixes as follows. Names ending in -ate become names ending in -ic. –Thus HNO 3 (aq), which contain a nitrate, becomes nitric acid. Names ending in -ite become names ending in -ous. –Thus HNO 2 (aq), which contain a nitrite, becomes nitrous acid.

56. Nomenclature of Acids (Cont’d) Names ending in -ide become names which start with hydro- name -ending with -ic. –Thus HF, which contains a fluoride, becomes hydrofluoric acid. Sulfur containing compounds are a special exception. –In these cases you add the ur in sulfur as part of the name of the acid. –They otherwise follow the normal naming rules. –H 2 S(aq) is thus hydrosulfuric acid NOT hydrosulfic acid.

57. Nomenclature of Acids (Cont’d) Phosphorous containing compounds are another special exception. –In these cases you add the or in as part of the name of the acid. –They otherwise follow the normal naming rules. –H 3 P(aq) is thus hydrophosphoric acid NOT hydrophosphfic acid.

58. Nomenclature of Acids Problems Name each of the following acids. HCl(aq) H 2 SO 4 (aq) HClO(aq) HClO 2 (aq) HClO 3 (aq) HClO 4 (aq)

59. Nomenclature of Acids Problems (Cont’d) Write formulas for each of the following acids. Hydrocyanic acid. Phosphoric acid. Hydrobromic acid. Sulfurous acid. Oxalic acid. Acetic acid.

60. Common Names Some compounds also have common names. –There are literally hundreds of such names. These names are often brand names or the names of commonly used substances. In other cases, there are multiple systematic names that could be used for the same compound so a common name is used instead.

61. Common Names (Cont’d) CompoundCommon NameSystematic Name NaClTable saltSodium chloride NaHCO 3 Baking sodaSodium hydrogen carbonate (sodium bicarbonate) MgSO 4 Epsom saltMagnesium sulfate Na 3 PO 4 Cleaning agentSodium phosphate Al(OH) 3 AntacidAluminum hydroxide NaOHDrain cleanerSodium hydroxide MgCO 3 Plaster of ParisMagnesium carbonate NaClOCloroxSodium hypochlorite CaCO 3 ChalkCalcium carbonate

62. Common Names (Cont’d) CompoundCommon NameSystematic Name H 2 OWaterDihydrogen monoxide (hydrogen oxide, hydroxic acid) H 2 O 2 Hydrogen peroxideDihydrogen dioxide (hydroperoxic acid) NH 3 AmmoniaNitrogen trihydride N 2 H 4 HydrazineDinitrogen tetrahydride CH 4 MethaneCarbon tetrahydride C 2 H 6 EthaneDicarbon hexahydride PH 3 PhosphinePhosphorous trihydride AsH 3 ArsineArsenic trihydride

63. Common Name Problems What are the systematic names and formulas for each of the following compounds? Water. Hydrogen peroxide. Table salt. Methane Ammonia.

64. Molecular and Formula Mass The molecular mass is the sum of all of the atomic masses of the atoms in a single molecule. The formula mass is the same thing except that it is the sum of all the atoms in a single formula unit. Most of the time the two will be exactly the same. –It is different for ionic compounds which are actually single large molecules. Because it is the mass for one molecule, a molecular or formula mass is normally given in units of amu.

65. Determination of Formula Mass Problems Determine the formula mass, in amu, of each of the following compounds: –NaCl –NH 3 –CaF 2

66. Significant Figures and Calculations Using Atomic Mass The number of atoms in a formula is considered exact. –So H 2 O contains exactly 2 hydrogens and 1 oxygen. Determination of formula mass is always treated as an addition problem for significant figures purposes.