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AP Notes Chapter 2 Molecules, Ions and Their Compounds.

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1 AP Notes Chapter 2 Molecules, Ions and Their Compounds

2 Chemical Compounds Chemical compounds result from the joining together of atoms Chemical compounds result from the joining together of atoms Chemical Bonds are the forces that hold atoms together. Chemical Bonds are the forces that hold atoms together. Chemical formulas are used to describe the number and kind of atoms in a compound Chemical formulas are used to describe the number and kind of atoms in a compound There are two major types of compounds that differ mostly by the way the atoms hold on to each other or the type of bond. There are two major types of compounds that differ mostly by the way the atoms hold on to each other or the type of bond.

3 Ionic compound are held together with an Ionic bond joining metal ions and non metal ionsIonic compound are held together with an Ionic bond joining metal ions and non metal ions Transfer of electrons cause the formation of ions or charged particlesTransfer of electrons cause the formation of ions or charged particles Ionic Compounds

4 Ions & Ionic Compounds Atoms or groups of atoms with a charge. Atoms or groups of atoms with a charge. Cations- positive ions - get by losing electrons(s). Metallic Cations- positive ions - get by losing electrons(s). Metallic Anions- negative ions - get by gaining electron(s). Nonmetallic Anions- negative ions - get by gaining electron(s). Nonmetallic It is these opposite charges that define an ionic compound and an ionic bond It is these opposite charges that define an ionic compound and an ionic bond Solid Ionic compounds are called salts. Solid Ionic compounds are called salts.

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6 Ionic Compounds Law of Definite Proportion- compounds have a constant composition. Law of Definite Proportion- compounds have a constant composition. Ions react in specific ratios by mass and charge. Ions react in specific ratios by mass and charge. Ionic compounds do not have a charge Ionic compounds do not have a charge Positive and negative charges balance Positive and negative charges balance Ions exist in small whole number ratios. Ions exist in small whole number ratios. Get charges from table, name of metal ion, or memorized from the list. Get charges from table, name of metal ion, or memorized from the list. Use parenthesis to indicate multiple polyatomics. Use parenthesis to indicate multiple polyatomics.

7 Naming Ionic Compounds Cation is wrtiten first in name and formula. Cation is wrtiten first in name and formula. If the cation is monoatomic- Name the metal (cation) just write the name. If the cation is monoatomic- Name the metal (cation) just write the name. If the cation is polyatomic- name it. If the cation is polyatomic- name it. THEN If the anion is monoatomic- name it but change the ending to –ide. THEN If the anion is monoatomic- name it but change the ending to –ide. If the anion is poly atomic- just name it If the anion is poly atomic- just name it Practice Ion names and formula w/charge Practice Ion names and formula w/charge

8 Naming Ionic Compounds Have to know what ions they form Have to know what ions they form off table, polyatomic, or figure it out off table, polyatomic, or figure it out CaS CaS K 2 S K 2 S AlPO 4 AlPO 4 K 2 SO 4 K 2 SO 4 FeS FeS CoI 3 CoI 3 Calcium sulfide Potassium sulfide Aluminum phosphate Potassium sulfate Iron II sulfideor Ferrous sulfide Cobalt III iodideor Cobaltic iodide

9 Naming Ionic Compounds Fe 2 (C 2 O 4 ) Fe 2 (C 2 O 4 ) MgO MgO MnO MnO KMnO 4 KMnO 4 NH 4 NO 3 NH 4 NO 3 Hg 2 Cl 2 Hg 2 Cl 2 Cr 2 O 3 Cr 2 O 3

10 Writing Ionic Formulas Sodium nitride Sodium nitride sodium- Na is always +1 sodium- Na is always +1 Nitride - ide tells you it comes from the table Nitride - ide tells you it comes from the table nitride is N -3 nitride is N -3 Doesnt add up to zero. Doesnt add up to zero. Na +1 N -3

11 Writing Ionic Formulas Sodium nitride Sodium nitride sodium- Na is always +1 sodium- Na is always +1 nitride - ide tells you it comes from the table nitride - ide tells you it comes from the table nitride is N -3 nitride is N -3 Doesnt add up to zero Doesnt add up to zero Need 3 Na Need 3 Na Na +1 N -3 Na 3 N

12 Ionic Compound Formulas Sodium sulfite Sodium sulfite calcium iodide calcium iodide Lead (II) oxide Lead (II) oxide Lead (IV) oxide Lead (IV) oxide Mercury (I) sulfide Mercury (I) sulfide Barium chromate Barium chromate Aluminum hydrogen sulfate Aluminum hydrogen sulfate Cerium (IV) nitrite Cerium (IV) nitrite Na 2 S CaI 2 PbO Pb 2 O 4 or PbO 2 Hg 2 S BaCrO 4 Al(HSO 4 ) 3 Ce(NO 3 ) 4

13 Covalent Compounds Composed of Molecules Composed of Molecules Law of Multiple Proportions- When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers. Law of Multiple Proportions- When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers. Chemical formula- the number and type of atoms in a molecule. Chemical formula- the number and type of atoms in a molecule. C 2 H carbon atoms, 6 hydrogen atoms C 2 H carbon atoms, 6 hydrogen atoms Structural formula shows the connections, but not necessarily the shape. Structural formula shows the connections, but not necessarily the shape.

14 Molecules differ by the number and kind of elements that make them up Molecules differ by the number and kind of elements that make them up Speculate on the formula of two oxides of carbon and oxygen Speculate on the formula of two oxides of carbon and oxygen Carbon monoxide = Carbon monoxide = Carbon dioxide = Carbon dioxide = Show that these compounds follow the law of multiple proportion. Show that these compounds follow the law of multiple proportion. Sometimes formula is not enough to get an adequate picture of a compound Sometimes formula is not enough to get an adequate picture of a compound CO CO2

15 H H HH H HCC There are also other models that attempt to show three dimensional shape. There are also other models that attempt to show three dimensional shape. Ball and stick. Ball and stick.

16 Covalent compounds Two words, with prefixes. Two words, with prefixes. Prefixes tell you how many. Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, septa, nona, deca mono, di, tri, tetra, penta, hexa, septa, nona, deca First element whole name with the appropriate prefix, except mono. First element whole name with the appropriate prefix, except mono. Second element, -ide ending with appropriate prefix. Second element, -ide ending with appropriate prefix. Practice Practice

17 Naming Covalent Compounds Two words, with prefixes Two words, with prefixes Prefixes tell you how many. Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, septa, nona, deca mono, di, tri, tetra, penta, hexa, septa, nona, deca First element whole name with the appropriate prefix, except mono First element whole name with the appropriate prefix, except mono Second element, -ide ending with appropriate prefix Second element, -ide ending with appropriate prefix Practice Practice

18 CO 2 CO 2 CO CO CCl 4 CCl 4 N 2 O 4 N 2 O 4 XeF 6 XeF 6 N 4 O 4 N 4 O 4 P 2 O 10 P 2 O 10 Naming Covalent Compounds

19 Covalent compounds The name tells you how to write the formula The name tells you how to write the formula Sulfur dioxide Sulfur dioxide difluorine monoxide difluorine monoxide nitrogen trichloride nitrogen trichloride diphosphorus pentoxide diphosphorus pentoxide

20 Summary for Writing Formulas and Names of Compounds Two sets of rules, ionic and covalent Two sets of rules, ionic and covalent To decide which to use, decide what the first word is. To decide which to use, decide what the first word is. If is a metal or polyatomic use ionic. If is a metal or polyatomic use ionic. If it is a non-metal use covalent. If it is a non-metal use covalent.

21 Acids Substances that produce H + ions when dissolved in water. Substances that produce H + ions when dissolved in water. All acids begin with H. All acids begin with H. Two types of acids: Two types of acids: Oxyacids Oxyacids Non-oxyacids Non-oxyacids

22 Naming acids If the formula has oxygen in it If the formula has oxygen in it write the name of the anion, but change write the name of the anion, but change ate to -ic acid ate to -ic acid ite to -ous acid ite to -ous acid Watch out for sulfuric and sulfurous Watch out for sulfuric and sulfurous H 2 CrO 4 H 2 CrO 4 HMnO 4 HMnO 4 HNO 2 HNO 2

23 Naming acids If the acid doesnt have oxygen If the acid doesnt have oxygen add the prefix hydro- add the prefix hydro- change the suffix -ide to -ic acid change the suffix -ide to -ic acid HCl HCl H 2 S H 2 S HCN HCN

24 Formulas for acids Backwards from names. Backwards from names. If it has hydro- in the name it has no oxygen If it has hydro- in the name it has no oxygen Anion ends in -ide Anion ends in -ide No hydro, anion ends in -ate or -ite No hydro, anion ends in -ate or -ite Write anion and add enough H to balance the charges. Write anion and add enough H to balance the charges.

25 Formulas for acids hydrofluoric acid hydrofluoric acid dichromic acid dichromic acid carbonic acid carbonic acid hydrophosphoric acid hydrophosphoric acid hypofluorous acid hypofluorous acid perchloric acid perchloric acid phosphorous acid phosphorous acid

26 Percent Composition Percent of each element a compound is composed of. Percent of each element a compound is composed of. Find the mass of each element, divide by the total mass, multiply by a 100. Find the mass of each element, divide by the total mass, multiply by a 100. Easiest if you use a mole of the compound. Easiest if you use a mole of the compound. Find the percent composition of CH 4 Find the percent composition of CH 4 Al 2 (Cr 2 O 7 ) 3 Al 2 (Cr 2 O 7 ) 3 CaSO 4 · 2H 2 O CaSO 4 · 2H 2 O

27 Working backwards From percent composition, you can determine the empirical formula. From percent composition, you can determine the empirical formula. Empirical Formula the lowest ratio of atoms in a molecule. Empirical Formula the lowest ratio of atoms in a molecule. Based on mole ratios. Based on mole ratios. A sample is 59.53% C, 5.38%H, 10.68%N, and 24.40%O what is its empirical formula. A sample is 59.53% C, 5.38%H, 10.68%N, and 24.40%O what is its empirical formula.

28 Sample Problem A gram sample of a compound (vitamin C) composed of only C, H, and O is burned completely with excess O g of CO 2 and g of H 2 O are produced. What is the empirical formula? A gram sample of a compound (vitamin C) composed of only C, H, and O is burned completely with excess O g of CO 2 and g of H 2 O are produced. What is the empirical formula?

29 Empirical To Molecular Formulas Empirical is lowest ratio. Empirical is lowest ratio. Molecular is actual molecule. Molecular is actual molecule. Need Molar mass. Need Molar mass. Ratio of empirical to molar mass will tell you the molecular formula. Ratio of empirical to molar mass will tell you the molecular formula. Must be a whole number because... Must be a whole number because...

30 Sample Problem A compound is made of only sulfur and oxygen. It is 69.6% S by mass. Its molar mass is 184 g/mol. What is its formula? A compound is made of only sulfur and oxygen. It is 69.6% S by mass. Its molar mass is 184 g/mol. What is its formula?

31 Hydrates Some salts trap water crystals when they form crystals. Some salts trap water crystals when they form crystals. These are hydrates. These are hydrates. Both the name and the formula needs to indicate how many water molecules are trapped. Both the name and the formula needs to indicate how many water molecules are trapped. In the name we add the word hydrate with a prefix that tells us how many water molecules. In the name we add the word hydrate with a prefix that tells us how many water molecules.

32 Hydrates In the formula you put a dot and then write the number of molecules. In the formula you put a dot and then write the number of molecules. Calcium chloride dihydrate Calcium chloride dihydrate Chromium (III) nitrate hexahydrate Chromium (III) nitrate hexahydrate CaCl 2 2 CaCl 2 2 Cr(NO 3 ) 3 6H 2 O


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