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Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 5 Molecules and Compounds.

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Presentation on theme: "Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 5 Molecules and Compounds."— Presentation transcript:

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2 Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 5 Molecules and Compounds

3 Tro's Introductory Chemistry, Chapter 5 2 Molecules and Compounds Molecules and Compounds Compounds = composed of 2 or more elements chemically combined Properties completely different from component elements Salt –Sodium (Na) – shiny, reactive, poisonous –Chlorine (Cl) – pale yellow gas, reactive, poisonous –Sodium chloride (NaCl) – table salt, flavor enhancer

4 Tro's Introductory Chemistry, Chapter 5 3 Pure substances have constant composition –all samples of a pure substance contain same elements in same ratios or proportions regardless of source –mixtures have variable composition Law of Constant Composition

5 Tro's Introductory Chemistry, Chapter 5 4 Compounds Display Constant Composition Water (H 2 O) decomposed by electrolysis yields 16.0 grams of oxygen to every 2.00 grams of hydrogen. Water has a constant Mass Ratio of Oxygen to Hydrogen of 8.0.

6 Tro's Introductory Chemistry, Chapter 5 5 Formulas Describe Compounds Compound = a distinct substance that is composed of atoms of two or more elements Formulas give the number and type of each atom in the simplest unit of the compound –Molecules (H 2 O) or ions (CaCl 2 ) Number of atoms of each element is written to the right of the element as a subscript –if only one atom, 1 subscript is not written Polyatomic groups are placed in parentheses –if more than one, i. e. Ca(NO 3 ) 2

7 Tro's Introductory Chemistry, Chapter 5 6 Formulas Describe Compounds Examples: water = H 2 O  two atoms of hydrogen and 1 atom of oxygen table sugar (sucrose) = C 12 H 22 O 11  12 atoms of C, 22 atoms of H and 11 atoms O

8 Tro's Introductory Chemistry, Chapter 5 7 Classifying Materials Atomic elements = elements whose particles are single atoms; Na, Ne, Hg, Ag Molecular elements = elements whose particles are multi-atom molecules; H 2, O 2, N 2, Cl 2

9 8 Molecular Elements Certain elements occur as 2 atom molecules Rule of 7’s –there are 7 common diatomic elements –find the element with atomic number 7, N –make a figure 7 by going over to Group 7A, then down –don’t forget to include H 2 H2H2 Cl 2 Br 2 I2I2VIIA N 2 O 2 F 2 7

10 Tro's Introductory Chemistry, Chapter 5 9 Classifying Materials Molecular compounds = compounds whose particles are molecules made of only nonmetals, i.e. CO 2 Ionic compounds = compounds whose particles are cations (+) and anions (-), i.e. NaCl

11 Tro's Introductory Chemistry, Chapter 5 10 Molecular Compounds Two or more nonmetals, i.e. H 2 O, CO 2, C 6 H 12 O 6 Smallest unit is a molecule

12 Tro's Introductory Chemistry, Chapter 5 11 Order of Elements in a Formula Metals written first –NaCl Nonmetals written in order from Table 5.1 –CO 2 –occasional exceptions for historical or informational reasons H 2 O, but NaOH Order of Listing Nonmetals in Chemical Formulas Table 5.1 FOClBrISHNPC

13 Tro's Introductory Chemistry, Chapter 5 12 Ionic Compounds Metals + nonmetals No individual molecule units, instead have a 3- dimensional array of cations and anions made of formula units

14 13 Molecular View of Elements and Compounds

15 Tro's Introductory Chemistry, Chapter 5 14 Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound aluminum, Al aluminum chloride, AlCl 3 chlorine, Cl 2 acetone, C 3 H 6 O carbon monoxide, CO cobalt, Co

16 Tro's Introductory Chemistry, Chapter 5 15 Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound aluminum, Al = atomic element aluminum chloride, AlCl 3 = ionic compound chlorine, Cl 2 = molecular element acetone, C 3 H 6 O = molecular compound carbon monoxide, CO = molecular compound cobalt, Co = atomic element

17 Tro's Introductory Chemistry, Chapter 5 16 Major Classes of Compounds Ionic –metal + nonmetal metal first in formula Binary Ionic –compounds with polyatomic ions Molecular –2 nonmetals Binary Molecular (or Binary Covalent) –Acids – formula starts with H though acids are molecular, they behave as ionic when dissolved in water may be binary or oxyacid

18 17 Binary Ionic Compounds: Writing a correct formula 1. Write down the charges of the stable ions with the positive ion first. Ex: for Chlorine and magnesium Mg Cl

19 18 2. Cross-over charges to get subscripts. Drop all +/- signs. Ex: for Chlorine and magnesium Mg Cl

20 19 3. Reduce/Simplify subscripts to get the lowest whole number ratio. The subscript “1” does not have to be shown. Ex: for Chlorine and magnesium MgCl 2 Ex: calcium and sulfur Ca +2 S -2 Ca 2 S 2 cross-over CaS simplify

21 20 How many electrons will an atom lose or gain in an ionic compound? lose 1 e - lose 2 e - lose 3 e - gain 3 e - gain 2 e - gain 1 e -

22 21 What will be the charge on the “stable ion” formed?

23 Tro's Introductory Chemistry, Chapter 5 22 Rules for Naming Ionic Compounds from Formula Made of cation and anion Name by simply naming the ions –If cation is: Type I metal (main group) = metal name Type II metal (transition element) = metal name(charge) Polyatomic ion = name of polyatomic ion –If anion is: Nonmetal = root of nonmetal name + ide Polyatomic ion = name of polyatomic ion

24 Tro's Introductory Chemistry, Chapter 5 23 Metal Cations Type I –metals whose ions can only have one possible charge IA, IIA, (Al, Ga, In) –determine charge by position on the Periodic Table IA = +1, IIA = +2, (Al, Ga, In = +3) Type II –metals whose ions can have more than one possible charge (transition elements) –determine charge by charge on anion How do you know a metal cation is Type II? its not Type I !!!

25 Tro's Introductory Chemistry, Chapter 5 24 Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms. lithium, Li copper, Cu gallium, Ga tin, Sn strontium, Sr

26 Tro's Introductory Chemistry, Chapter 5 25 Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms. lithium, LiType I+1 copper, CuType II gallium, GaType I+3 tin, SnType II strontium, SrType I+2

27 Tro's Introductory Chemistry, Chapter 5 26 Determining Charge and Naming Monatomic Nonmetal Anions Determine the charge from position on the Periodic Table To name anion, change ending on the element name to –ide 4A = -4 5A = -3 6A = -2 7A = -1 C = carbide N = nitride O = oxide F = fluoride Si = silicide P = phosphide S = sulfide Cl = chloride

28 27 Naming Type I Binary Ionic Compounds Contain Metal Cation + Nonmetal Anion Metal listed first in formula & name 1. name metal cation first, name nonmetal anion second 2. cation name is the metal name 3. nonmetal anion named by changing the ending on the nonmetal name to -ide

29 28 What is the correct formula and name for a compound made from: 1. nitrogen and potassium 2. magnesium and oxygen 3. chlorine and calcium 4. oxygen and aluminum

30 29 1. nitrogen and potassium K 3 Npotassium nitride 2. magnesium and oxygen MgOmagnesium oxide 3. chlorine and calcium CaCl 2 calcium chloride 4. oxygen and aluminum Al 2 O 3 aluminum oxide

31 Tro's Introductory Chemistry, Chapter 5 30 Naming Type II Binary Ionic Compounds Name metal cation first, name nonmetal anion second Metal cation name is the metal name followed by a Roman Numeral in parentheses to indicate its charge –determine charge from anion charge –Common Type II cations in Table 5.5 Nonmetal anion named by changing the ending on the nonmetal name to -ide

32 Tro's Introductory Chemistry, Chapter 5 31 Example – Naming Binary Ionic, Type II Metal CuCl 1. Identify Major Class Cu = metal, on left side of Periodic Table Cl = nonmetal, on right side of Periodic Table  Ionic  Ionic 2. Identify the Subclass 2 elements,  Binary Ionic 3. Is the metal Type I or Type II Cu not in Group IA, IIA, or (Al, Ga, In)  Type II

33 Tro's Introductory Chemistry, Chapter 5 32 Example – Naming Binary Ionic, Type II Metal CuCl 4. Identify cation and anion Cl = Cl - because it is Group 7 Cu = Cu + to balance the charge 5. Name the cation Cu + = copper( I ) 6. Name the anion Cl - = chloride 7. Write the cation name first, then the anion name copper( I ) chloride

34 33 Give the formula and name for a compound from Cu +1 and sulfur Cu +1 S -2 formula = Cu 2 S name = copper( I ) sulfide

35 34 Give the formula and name for a compound from Fe +2 and chlorine Fe +2 Cl -1 formulaFeCl 2 formula = FeCl 2 name= iron( II ) chloride name = iron( II ) chloride Give the formula and name for a compound from Cu +2 and sulfur Cu +2 S -2 formula = CuS name = copper( II ) sulfide

36 35 What is the formula for copper( II ) oxide? Cu +2 O -2 formula = CuO

37 Tro's Introductory Chemistry, Chapter 5 36 Compounds with Polyatomic Ions Polyatomic ions are single ions that contain more than one atom Formula: cation first, polyatomic anion or polyatomic cation, monatomic anion Name cation first and then anion –Non-polyatomic cations named like Type I and II –Non-polyatomic anions named with –ide –Polyatomic ions = use name of polyatomic ion

38 Tro's Introductory Chemistry, Chapter 5 37 Some Common Polyatomic Ions (be able to recognize these) Name Formula and Charge acetate C2H3O2–C2H3O2–C2H3O2–C2H3O2– carbonate CO 3 2– hydrogen carbonate (aka bicarbonate) HCO 3 – hydroxide OH – nitrate NO 3 – nitrite NO 2 – sulfate SO 4 2– chlorate ClO 3 – ammonium NH 4 +

39 Tro's Introductory Chemistry, Chapter 5 38 Naming Ionic Compounds with Polyatomic Ion Na 2 SO 4 1. Identify Major Class Na = metal, on the left side of Periodic Table SO 4 = is a polyatomic ion,  Ionic 2. Identify the Subclass compound has 3 elements  Ionic with Polyatomic Ion 3. Is the metal Type I or Type II Na is in Group IA,  Type I

40 Tro's Introductory Chemistry, Chapter Identify the ions Na = Na + because in Group 1 SO 4 = SO 4 2- a polyatomic ion 5.Name the cation Na + = sodium (Type I) 6.Name the anion SO 4 2- = sulfate 7.Write the name of the cation followed by the name of the anion sodium sulfate Naming Ionic Compounds with Polyatomic Ion Na 2 SO 4

41 Tro's Introductory Chemistry, Chapter 5 40 Naming Ionic Compounds with Polyatomic Ion Fe(NO 3 ) 3 1.Identify Major Class Fe = metal, on left side of Periodic Table NO 3 = is a polyatomic ion because it is in ( )  Ionic 2.Identify the Subclass Have 3 elements  Ionic with Polyatomic Ion 3.Is the metal Type I or Type II Fe not in Group IA, IIA, or (Al, Ga, In)  Type II

42 Tro's Introductory Chemistry, Chapter 5 41 Naming Ionic compounds with Polyatomic Ion Fe(NO 3 ) 3 5. Identify the ions NO 3 = NO 3 - a polyatomic ion Fe = Fe +3 to balance the charge of the 3 NO Name the cation Fe +3 = iron( III ) (Type II ) 7. Name the anion NO 3 - = nitrate 8. Write the name of the cation followed by the name of the anion iron( III ) nitrate

43 Tro's Introductory Chemistry, Chapter 5 42 Rules for Naming Binary Molecular Compounds Binary molecular compounds = composed of 2 nonmetal elements for binary molecular compound: –name first nonmetal –then name second nonmetal with ide ending –then give each name a prefix to indicate number of atoms (subscript) of each element in formula

44 43 Naming Binary Molecular Compounds 1. Name first element in formula first –use the full name of the element 2. Name the second element in the formula with an -ide –as if it were an anion, however, remember these compounds do not contain ions! 3. Use a prefix in front of each name to indicate the number of atoms a)Never use the prefix mono- on the first element

45 Tro's Introductory Chemistry, Chapter 5 44 Subscript - Prefixes 1 = mono-; –not used on first nonmetal 2 = di- 3 = tri- 4 = tetra- 5 = penta- 6 = hexa- 7 = hepta- 8 = octa- drop last “a” if name begins with vowel

46 Tro's Introductory Chemistry, Chapter 5 45 Naming Binary Molecular Compounds BF 3 1. Identify Major Class B = nonmetal, on right side of Periodic Table F = nonmetal, on right side of Periodic Table  Molecular 2. Identify the Subclass 2 elements  Binary Molecular

47 Tro's Introductory Chemistry, Chapter 5 46 Naming Binary Molecular Compounds BF 3 4. Name the first element: boron 5. Name the second element with an –ide fluorine  fluoride 6. Add a prefix to each name to indicate the subscript monoboron, trifluoride 7. Write the first element with prefix, then the second element with prefix –Drop prefix mono from first element boron trifluoride

48 Tro's Introductory Chemistry, Chapter 5 47 Formula Mass Formula mass = mass of an individual molecule or formula unit also known as molecular mass or molecular weight Sum of the masses of the atoms in a single molecule or formula unit –whole = sum of the parts! mass of 1 molecule of H 2 O = 2(1.01 amu H) amu O = amu


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