Naming Ionic and Covalent Compounds

1. Naming Ionic and Covalent Compounds

2. Compounds A compound is a substance composed of two or more elements combined in a specific ratio and held together by chemical bonds. Familiar examples of compounds are water and salt (sodium chloride).

3. Ionic Compounds and Bonding The resulting electrically neutral compound, sodium chloride, is represented with the chemical formula NaCl. The chemical formula, or simply formula, of an ionic compound denotes the constituent elements and the ratio in which they combine.

4. Naming Ions and Ionic Compounds A monatomic ion is named by changing the ending of the element’s name to –ide. Cl– is chloride O2– is oxide Some metals can form cations of more than one possible charge. Fe2+ : ferrous ion [Fe(II)] Fe3+ : ferric ion [Fe(III)] Mn2+ : manganese(II) ion Mn3+ : manganese(III) ion Mn4+ : manganese(IV) ion

5. Naming Ions and Ionic Compounds

6. Naming Ions and Ionic Compounds Formulas for ionic compounds are generally empirical formulas. Ionic compounds are electronically neutral.

7. Formulas of Ionic Compounds Al3+ O2– In order for ionic compounds to be electronically neutral, the sum of the charges on the cation and anion in each formula must be zero. Aluminum oxide: Al2O3 Sum of charges: 2(+3) + 3(–2) = 0

8. Formulas of Ionic Compounds

9. Naming Ions and Ionic Compounds To name ionic compounds: 1) Name the cation • omit the word ion • use a Roman numeral if the cation can have more than one charge 2) Name the anion • omit the word ion Examples: NaCN sodium cyanide FeCl2 iron(II) chloride FeCl3 iron(III) chloride

10. Covalent Bonding in Ionic Species Ca2+ PO43– Polyatomic ions consist of a combination of two or more atoms. Formulas are determined following the same rule as for ionic compounds containing only monatomic ions: ions must combine in a ratio that give a neutral formula overall. Calcium phosphate: Ca3(PO4)2 5.7 Sum of charges: 3(+2) + 2(–3) = 0

11. Covalent Bonding in Ionic Species

12. Covalent Bonding in Ionic Species

13. Worked Example 5.9 Name the following ionic compounds: (a) Fe2(SO4)3, (b) Al(OH)3, and (c) Hg2O. Strategy Begin by identifying the cation and anion in each compound, and then combine the names for each, eliminating the word ion. Solution (a) Fe2(SO4)3 is iron(III) sulfate. (b) Al(OH)3 is aluminum hydroxide. (c) Hg2O is mercury(I) oxide. Think About It Be careful not to confuse the subscript in the formula with the charge in the metal ion. In part (a), for example, the subscript on Fe is 2, but this is an iron(III) compound.

14. Covalent Bonding in Ionic Species Oxoanions are polyatomic anions that contain one or more oxygen atoms and one atom (the “central atom”) of another element. Starting with the oxoanions that end in –ate, we can name these ions as follows: The ion with one more O atom than the –ate ion is called the per…ate ion. Thus, ClO3- is the chlorate ion, so ClO4- is the perchlorate ion. The ion with one less O atom than the –ate ion is called the –ite ion. Thus, ClO2- is the chlorite ion. The ion with two fewer O atom than the –ate ion is called the hypo…ite ion. Thus, ClO- is the hypochlorite ion. At minimum, memorize the oxoanions that end in –ate so you can apply these guidelines when necessary.

15. Covalent Bonding in Ionic Species perchlorate ClO4- chlorate ClO3- chlorite ClO2- hypochlorite ClO- nitrate NO3- nitrite NO2- phosphate PO43- phosphite PO33- sulfate SO42- sulfite SO32-

16. Worked Example 5.10 Name the following species: (a) BrO4-, (b) HCO3-, and (c) H2CO3. Strategy Each species is either an oxoanion or an oxoacid. Identify the “reference oxidation” (the one with the –ate ending) for each, and apply the rules to determine appropriate names. Think About ItRemembering all these names and formulas is greatly facilitated by memorizing the common ions that end in –ate. chlorate ClO3- nitrate NO3- iodate IO3- carbonate CO32- bromate BrO3- oxalate C2O42- sulfate SO42- chromate CrO42- phosphate PO43- permanganate MnO4- Solution (a) BrO4- has one more O atom than the bromate ion (BrO3-), so BrO4- is the perbromate ion. (b) CO32- is the carbonate ion. Because HCO3- has one ionizable hydrogen atom, it is called the hydrogen carbonate ion. (c) With two ionizable hydrogen atoms and no charge on the compound, H2CO3 is carbonic acid. Think About It Make sure that the charges sum to zero in each compound formula. In part (a), for example, Hg2+ + 2Cl- = (+2) + 2(-1) = 0; in part (b), (+2) + 2(-1) = 0; and in part (c), 3(+1) + (-3) = 0.

17. Worked Example 5.11 Determine the formula of sulfurous acid. Strategy The –ous ending in the name of an acid indicates that the acid is derived from an oxoanion ending in –ite. The oxoanion must be sulfite, SO32-, so add enough hydrogen ions to make a neutral formula. Solution The formula of sulfurous acid is H2SO3. Think About It Remembering all these names and formulas is greatly facilitated by memorizing the common ions that end in -ate.

18. Hydrates A hydrate is a compound that has a specific number of water molecules within its solid structure. For example, in its normal state, copper(II) sulfate has five water molecules associated with it. Systematic name: copper(II) sulfate pentahydrate Formula: Cu(SO)4 ∙ 5H2O Some other hydrates are BaCl2 ∙ 2H2O LiCl ∙ H2O MgSO4 ∙ 7H2O Sr(NO3)2 ∙ 4H2O

19. Hydrates When the water molecules are driven off by heating, the resulting compound, Cu(SO)4, is sometimes called anhydrous copper(II) sulfate. Anhydrous means the compound no longer has water molecules associated with it.

20. Familiar Inorganic Compounds

21. Covalent Bonding and Molecules

22. Covalent Bonding and Molecules A chemical formula denotes the composition of the substance. A molecular formulashows the exact number of atoms of each element in a molecule. Some elements have two or more distinct forms known as allotropes. • For example, oxygen (O2) and ozone (O3) are allotropes of oxygen. A structural formulashows not only the elemental composition, but also the general arrangements.

23. Covalent Bonding and Molecules Molecular substances can also be represented using empirical formulas, the whole-number ratio of elements. While, the molecular formulas tell us the actual number of atoms (the true formula), the empirical formula gives the simplest formula. Molecular formula: N2H4 Empirical formula: NH2 The molecular and empirical formulas are often the same.

24. Covalent Bonding and Molecules

25. Naming Molecular Compounds Remember that binary molecular compounds are substances that consist of just two different elements. Nomenclature: 1) Name the first element that appears in the formula. 2) Name the second element that appears in the formula, changing its ending to –ide. Examples: HCl hydrogen chloride HI hydrogen iodide 5.6

26. Naming Molecular Compounds Greek prefixes are used to denote the number of atoms of each element present.

27. Naming Molecular Compounds • The prefix mono- is generally omitted for the first element. • For ease of pronunciation, we usually eliminate the last letter of a prefix that ends in “o” or “a” when naming an oxide. • Example: N2O5 is dinitrogen pentoxide not dinitrogen pentaoxide

28. Worked Example 5.7 Name the following binary molecular compounds: (a) NF3 and (b) N2O4. Strategy Each compound will be named using the systematic nomenclature including, where necessary, appropriate Greek prefixes. Solution (a) nitrogen trifluoride (b) dinitrogen tetroxide Think About It Make sure that the prefixes match the subscripts in the molecular formulas and that the word oxide is not preceded immediately by an “a” or an “o”.

29. Worked Example 5.8 Write the chemical formulas for the following binary molecular compounds: (a) sulfur tetrafluoride and (b) tetraphosphorus decasulfide. Strategy The formula for each compound will be deduced using the systematic nomenclature guidelines. Solution (a) SF4 (b) P4S10 Think About It Double-check that the subscripts in the formulas match the prefixes in the compound names: (a) 4 = tetra and (b) 4 = tetra and 10 = deca.

30. Compounds Containing Hydrogen The names of molecular compounds containing hydrogen do not usually conform to the systematic nomenclature guidelines. Many are called by the common, nonsystematic names or by names that do not indicate explicitly the number of H atoms present. Examples: B2H6 Diborane SiH4 Silane NH3 Ammonia PH3 Phosphine H2O Water H2S Hydrogen sulfide

31. Compounds Containing Hydrogen One definition of an acid is a substance that produces hydrogen ions (H+) when dissolved in water. HCl is an example of a binary compound that is an acid when dissolved in water. To name these types of acids: 1) remove the –gen ending from hydrogen 2) change the –ide ending on the second element to –ic. hydrogen chloride → hydrochloric acid

32. Compounds Containing Hydrogen A compound must contain at least one ionizable hydrogen atomto be an acid upon dissolving.

33. Organic Compounds Our nomenclature discussion so far has focused on inorganic compounds, generally defined as those without carbon. Organic compounds contain carbon and hydrogen, sometimes in combination with other atoms. Hydrocarbons contain only carbon and hydrogen. The simplest hydrocarbons are called alkanes.

34. Organic Compounds

35. Organic Compounds

36. Organic Compounds Many organic compounds contain groups of atoms known as functional groups, which often determine a molecule’s reactivity.

37. H2 H2O NH3 CH4 A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds A diatomic molecule contains only two atoms H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4

38. Writing Chemical Formals There are 7 elements that occur in nature as a diatomic molecule One way to remember these elements is: Mr. BrINClHOF

39. A monatomic ion contains only one atom Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3-

40. 2.5

41. Guidelines for Writing Chemical Formulas for Binary Compounds • Except for Hydrogen, the element farther to the left in the • periodic table appears first. Ie: KCl, PCl3, Al2S3, and Fe3O4 • If hydrogen is present, it appears last except when the other • element is from group 16 or 17. Ie: LiH, NH3, B2H6, CH4 • H2O, HCl and HI • If both elements are from the same group, the lower one • appears first. Ie: SiC and BrF3

42. molecular empirical H2O A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2O CH2O C6H12O6 O3 O N2H4 NH2

43. ionic compounds consist of a combination of cations and an anions • the formula is always the same as the empirical formula • the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl

44. 2 x +3 = +6 1 x +2 = +2 1 x +2 = +2 3 x -2 = -6 2 x -1 = -2 1 x -2 = -2 Formula of Ionic Compounds Al2O3 Al3+ O2- CaBr2 Ca2+ Br- Na2CO3 Na+ CO32-

45. Ion Name (common name) Ion Name (Common name) NH4+ Ammonium CO32- Carbonate H3O+ Hydronium HCO3- Hydrogen carbonate (bicarbonate) OH- Hydroxide SO32- Sulfite CN- Cyanide HSO3- Hydrogen sulfite NO2- Nitrite SO42- Sulfate NO3- Nitrate HSO4- Hydrogen sulfate ClO- Hypochlorite (often written OCl-) SCN- Thiocyanate ClO2- Chlorite S2O32- Thiosulfate ClO3- Chlorate CrO42- Chromate ClO4- Perchlorate Cr2O72- Dichromate MnO4- Permanganate PO43- Phosphate CH3CO2- Acetate (can be written C2H3O2-) HPO42- Hydrogen phosphate C2O42- Oxalate H2PO4- Dihydrogen phospate M U S T K N O W

46. Recognizing Ionic Compounds A compound is ionic if it contains a metal from group 1 Or group 2 or one of the polyatomic ions. Binary metal Oxides and sulfides also have ionic character

47. Chemical Nomenclature • Ionic Compounds • often a metal + nonmetal • anion (nonmetal), add “ide” to element name barium chloride BaCl2 potassium oxide K2O magnesium hydroxide Mg(OH)2 potassium nitrate KNO3

48. Cations of Variable Charge Transition metals such as copper may form cations Of different charge. This is represented by placing a Roman numeral after the transition metal in Parentheses after the name of the metal. CuO Copper(II) oxide Cu2O Copper(I) oxide

49. Transition metal ionic compounds • indicate charge on metal with Roman numerals iron(II) chloride FeCl2 2 Cl- -2 so Fe is +2 FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide

50. Molecular compounds • nonmetals or nonmetals + metalloids • common names • H2O, NH3, CH4, C60 • element further left in periodic table is 1st • element closest to bottom of group is 1st • if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom • last element ends in ide