Atoms, Molecules, and Ions Chapter 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2.6 Chemical Formulas Molecular formula Molecular Model Structural formula Empirical formula Formula of ionic Compound 分子式 分子模型 結構式 經驗式 離子化合物公式

3 Formulas and Models

4 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. H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2

5 Ionic compounds consist of a combination of cations and anions. The formula is usually 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

6 The most reactive metals (green) and the most reactive nonmetals (blue) combine to form ionic compounds.

7 Formulas of Ionic Compounds Al 2 O 3 2 x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 2 x +1 = +21 x -2 = -2 Na + CO 3 2-

Example 2.4 Write the formula of magnesium nitride, containing the Mg 2+ and N 3− ions. When magnesium burns in air, it forms both magnesium oxide and magnesium nitride.

Example 2.4 Strategy Our guide for writing formulas for ionic compounds is electrical neutrality; that is, the total charge on the cation(s) must be equal to the total charge on the anion(s). Because the charges on the Mg 2+ and N 3− ions are not equal, we know the formula cannot be MgN. Instead, we write the formula as Mg x N y, where x and y are subscripts to be determined.

Example 2.4 Solution To satisfy electrical neutrality, the following relationship must hold: (+2)x + (−3)y = 0 Solving, we obtain x/y = 3/2. Setting x = 3 and y = 2, we write Check The subscripts are reduced to the smallest whole- number ratio of the atoms because the chemical formula of an ionic compound is usually its empirical formula.

Chemical Nomenclature 化學命名 11

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13 Chemical Nomenclature Ionic Compounds 離子化合物 –Often a metal + nonmetal ( 金屬 + 非金屬 ) –Anion (nonmetal), add “-ide” to element name ( 陰離子非金屬元素名稱後加 -ide) BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate 氯化鋇 氧化鉀 氫氧化鎂 硝酸鉀

14 Transition metal ionic compounds –indicate charge on metal with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2 iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3 iron(III) chloride Cr 2 S 3 3 S so Cr is +3 (6/2) chromium(III) sulfide

Naming Compounds I. Ionic CompoundsIonic Compounds cation + anions  Potassium Bromide  Zinc Iodide  Aluminum Oxide  Lithium hydroxide  Potassium cyanide KBr 溴化鉀 ZnI 2 碘化鋅 Al 2 O 3 氧化鋁 LiOH 氫氧化鋰 KCN 氰化鉀

Transition metal with different charge MnO Mn 2 O 3 MnO 2  Manganese (II) oxide  Manganese (III) oxide  Manganese (IV) oxide Mn 2+ Mn 3+ Mn 4+

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Example 2.5 Name the following compounds: (a)Cu(NO 3 ) 2 (b)KH 2 PO 4 (c)NH 4 ClO 3 copper(II) nitrate potassium dihydrogen phosphate. ammonium chlorate

Example 2.5 Strategy Note that the compounds in (a) and (b) contain both metal and nonmetal atoms, so we expect them to be ionic compounds. There are no metal atoms in (c) but there is an ammonium group, which bears a positive charge. So NH 4 ClO 3 is also an ionic compound. Our reference for the names of cations and anions is Table 2.3. Keep in mind that if a metal atom can form cations of different charges (see Figure 2.11), we need to use the Stock system.

Example 2.5 Solution (a)The nitrate ion ( ) bears one negative charge, so the copper ion must have two positive charges. Because copper forms both Cu + and Cu 2+ ions, we need to use the Stock system and call the compound copper(II) nitrate. (b)The cation is K + and the anion is (dihydrogen phosphate). Because potassium only forms one type of ion (K + ), there is no need to use potassium(I) in the name. The compound is potassium dihydrogen phosphate. (c) The cation is (ammonium ion) and the anion is. The compound is ammonium chlorate.

Example 2.6 Write chemical formulas for the following compounds: (a)mercury(I) nitrite (b)cesium sulfide (c)calcium phosphate Hg 2 (NO 2 ) 2 Cs 2 S Ca 3 (PO 4 ) 2

Example 2.6 Strategy We refer to Table 2.3 for the formulas of cations and anions. Recall that the Roman numerals in the Stock system provide useful information about the charges of the cation.

Example 2.6 Solution (a)The Roman numeral shows that the mercury ion bears a +1 charge. According to Table 2.3, however, the mercury(I) ion is diatomic (that is, ) and the nitrite ion is. Therefore, the formula is Hg 2 (NO 2 ) 2. (b)Each sulfide ion bears two negative charges, and each cesium ion bears one positive charge (cesium is in Group 1A, as is sodium). Therefore, the formula is Cs 2 S.

Example 2.6 (c) Each calcium ion (Ca 2+ ) bears two positive charges, and each phosphate ion ( ) bears three negative charges. To make the sum of the charges equal zero, we must adjust the numbers of cations and anions: 3(+2) + 2(−3) = 0 Thus, the formula is Ca 3 (PO 4 ) 2.

26 Molecular compounds 分子化合物 −Nonmetals or nonmetals + metalloids −Common names −H 2 O, NH 3, CH 4 −Element furthest to the left in a period and closest to the bottom of a group on periodic table is placed first in formula −If more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom −Last element name ends in -ide

Naming Compounds II. Molecular compoundsMolecular compounds First element + second element-ide  Hydrogen chloride  Hydrogen bromide  Silicon carbide HCl HBr SiC

Naming Compounds II. Carbon monoxide Carbon dioxide Sulfur dioxide Sulfur trioxide Nitrogen dioxide Dinitrogen tetroxide COCO2SO2SO3NO2N2O4COCO2SO2SO3NO2N2O4 Using Greek prefixes to denote the number of atoms of each element

29 HI hydrogen iodide 碘化氫 NF 3 nitrogen trifluoride 三氟化氮 SO 2 sulfur dioxide 二氧化硫 N 2 Cl 4 dinitrogen tetrachloride 四氯化二氮 NO 2 nitrogen dioxide 二氧化氮 N2ON2O dinitrogen monoxide 一氧化二氮 Molecular Compounds

Greek Prfixes 希臘字首

Example 2.7 Name the following molecular compounds: (a)SiCl 4 (b)P 4 O 10 silicon tetrachloride tetraphosphorus decoxide

Example 2.7 Strategy We refer to Table 2.4 for prefixes. In (a) there is only one Si atom so we do not use the prefix “mono.” Solution (a)Because there are four chlorine atoms present, the compound is silicon tetrachloride. (b)There are four phosphorus atoms and ten oxygen atoms present, so the compound is tetraphosphorus decoxide. Note that the “a” is omitted in “deca.”

Example 2.8 Write chemical formulas for the following molecular compounds: (a)carbon disulfide (b) disilicon hexabromide CS 2 Si 2 Br 6

Example 2.8 Strategy Here we need to convert prefixes to numbers of atoms (see Table 2.4). Because there is no prefix for carbon in (a), it means that there is only one carbon atom present. Solution (a)Because there are two sulfur atoms and one carbon atom present, the formula is CS 2. (b) There are two silicon atoms and six bromine atoms present, so the formula is Si 2 Br 6.

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ACIDS 酸類的命名 36

Acid Oxoacid Oxoanion Base 酸 含氧酸 含氧陰離子 鹼 37

38 An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. For example: HCl gas and HCl in water Pure substance, hydrogen chloride Dissolved in water (H 3 O + and Cl − ), hydrochloric acid

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40 An oxoacid is an acid that contains hydrogen, oxygen, and another element. HNO 3 nitric acid H 2 CO 3 carbonic acid H 3 PO 4 phosphoric acid

Naming Compounds IV. Acid An acid is a substances that yields hydrogen ions H + when dissolved in water.

Naming Compounds IV. Acids Acids that contain hydrogen, oxygen, and other element are called oxoacids.  Carbonic acid  Chloric acid  Nitric acid  Phosphoric acid  Sulfuric acid H 2 CO 3 碳酸 HClO 3 氯酸 HNO 3 硝酸 H 3 PO 4 磷酸 H 2 SO 4 硫酸

Naming Compounds IV. Acids Oxoacids have the same central atom but a different number of O atoms. Addition of one O atom “ – ic” acid  “per … – ic” acid HClO 3  HClO 4 Chloric acid  perchloric acid

Naming Compounds IV. Acids Oxoacids have the same central atom but a different number of O atoms. Removal of one O atom “ – ic” acid  “ – ous” acid HNO 3  HNO 2 nitric acid  nitrous acid

Naming Compounds IV. Acids Oxoacids have the same central atom but a different number of O atoms. Removal of two O atom “ – ic” acid  “hypo … – ous” acid HBrO 3  HBrO bromic acid  hypobromous acid

Naming Compounds IV. Acids Oxoanions: anions of oxoacids When all the H ion are removed from “– ic” acid “ – ic” acid  “– ate” H 2 CO 3  CO 3 2- carbonic acid  carbonate

Naming Compounds IV. Acid and Bases Oxoanions: anions of oxoacids When all the H ion are removed from “– ous” acid “ – ous” acid  “– ite” H 2 SO 3  SO 3 2- sulfurous acid  sulfurate

48 過氯酸 氯酸 亞氯酸 次氯酸 過氯酸根 氯酸根 亞氯酸根 次氯酸根

Naming Compounds IV. Acids Oxoanions: anions of oxoacids Removal of hydrogen  Phosphoric acid  Dihydrogen phosphate  Hydrogen phosphate  Phosphate H 3 PO 4 H 2 PO 4 _ HPO 4 2 _ PO 4 3 _

50 Naming Oxoacids and Oxoanions 含氧酸 含氧酸根離子 含氧陰離子

51 The rules for naming oxoanions, anions of oxoacids, are as follows: 1. When all the H ions are removed from the “-ic” acid, the anion’s name ends with “-ate.” 2. When all the H ions are removed from the “-ous” acid, the anion’s name ends with “-ite.” 3. The names of anions in which one or more but not all the hydrogen ions have been removed must indicate the number of H ions present. For example: –H 2 PO 4 - dihydrogen phosphate –HPO 4 2- hydrogen phosphate –PO 4 3- phosphate

Example 2.9 Name the following oxoacid and oxoanion: (a)H 3 PO 3 (b)

Example 2.9 Strategy To name the acid in (a), we first identify the reference acid, whose name ends with “ic,” as shown in Figure In (b), we need to convert the anion to its parent acid shown in Table 2.6. Solution (a)We start with our reference acid, phosphoric acid (H 3 PO 4 ). Because H 3 PO 3 has one fewer O atom, it is called phosphorous acid. (b)The parent acid is HIO 4. Because the acid has one more O atom than our reference iodic acid (HIO 3 ), it is called periodic acid. Therefore, the anion derived from HIO 4 is called periodate.

BASES 鹼類的命名 54

55 A base can be defined as a substance that yields hydroxide ions (OH - ) when dissolved in water. NaOH sodium hydroxide 氫氧化鈉 KOH potassium hydroxide 氫氧化鉀 Ba(OH) 2 barium hydroxide 氫氧化鋇

HYDRATES 水合物的命名 56

57 Hydrates are compounds that have a specific number of water molecules attached to them. BaCl 2 2H 2 O LiClH 2 O MgSO 4 7H 2 O Sr(NO 3 ) 2 4H 2 O barium chloride dihydrate lithium chloride monohydrate magnesium sulfate heptahydrate strontium nitrate tetrahydrate CuSO 4 5H 2 O CuSO 4

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59 Organic chemistry is the branch of chemistry that deals with carbon compounds. C H H H OH C H H H NH 2 C H H H COH O methanolmethylamineacetic acid Functional Groups:

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