Chapter 3 Notes

1

3Chemistry: A Molecular Approach by Nivaldo J. TroChemistry: A Molecular Approach by Nivaldo J. TroCHEM 1411 General ChemistryCHEM 1411 General Chemistry

Mr. Kevin A. BoudreauxAngelo State Universitywww.angelo.edu/faculty/kboudrea

Mr. Kevin A. BoudreauxAngelo State Universitywww.angelo.edu/faculty/kboudrea

Molecules, Compounds, Molecules, Compounds, and Chemical Equationsand Chemical Equations

Chapter Objectives:• Learn the basic concepts behind chemical bonds.• Learn how to write formulas and name chemical

compounds.• Learn how to use percent compositions to find

empirical and molecular formulas.• Learn how to balance chemical equations.

2

Chemical CompoundsChemical Compounds• Most substances that we encounter are compounds,

not elements.

• A chemical compound is a pure substance formed from the combination of two or more different elements. The properties of the compound may be completely unlike those of the elements that form it.

• The formula for a compound lists the symbols of the individual elements followed by subscripts which indicate the number of atoms of that element. (If no subscript is given, it is understood to be “1.”) E.g., NaCl, H2O, C12H22O11.

Chapter 3 Notes

3

Ionic and Molecular Ionic and Molecular CompoundsCompounds

4

Elements and CompoundsElements and Compounds• Elements and compounds can be further subdivided,

as shown below:

Chapter 3 Notes

5

Types of BondingTypes of Bonding• When two atoms collide during a reaction, it is the

electrons that make the actual contact, since they occupy a much greater volume than the nucleus.

• Thus, it is the electrons that form the connections, or chemical bonds, that join atoms together to form compounds.

• Elements combine to form compounds in two different ways:– transferring electrons from atoms of one

element to another results in ionic bonds.– sharing electrons between atoms of different

elements results in covalent bonds.

6

Ionic Bonds and Ionic CompoundsIonic Bonds and Ionic Compounds• Ionic bonds form when one atoms transfers one or

more electrons to another atom, producing ions. • Ionic compounds are compounds that are held

together by ionic bonds between positively-charged cations and negatively-charged anions.

• Ionic compounds generally result when a metal combines with a nonmetal:– Metal + Nonmetal → ionic compound– Metal + Polyatomic ion → ionic compound– In general, metals tend to give up electrons, while

nonmetals accept electrons.

Chapter 3 Notes

7

Ionic Bonds and Ionic CompoundsIonic Bonds and Ionic Compounds

Figure 3.1

8

Ionic Bonds and Ionic CompoundsIonic Bonds and Ionic Compounds• The ionic bond is the strong attraction between the

cations and the anions. Unlike molecules, the cation and anion are not physically joined together.

• Thus, there is no molecule of NaCl; ionic compounds instead form ionic solids, which contain equal amounts of positive and negative charge surrounding each other in a regular array called a crystal.

Chapter 3 Notes

9

Ionic Bonds and Ionic CompoundsIonic Bonds and Ionic Compounds• The smallest unit of an ionic compound is the

formula unit, the smallest electrically neutral collection of ions.

• Monatomic ions are cations or anions derived from a single atom, such as Cl-, O2-, Na+, and Mg2+.

• Polyatomic ions are combinations of atoms that possess an overall charge, such as CO3

2-, SO42-,

NO3-, CN-, NH4

+, C2H3O2-, etc.

• Ionic compounds are electrically neutral — there must be the same amount of positive charge as there is negative charge.

10

Examples: Writing Ionic FormulasExamples: Writing Ionic Formulas1. Write the formula for the ionic compound formed

between the following pairs of elements and provide a name for the compound.

a. Al and F

b. Na and S

c. Ba and S

d. Mg and P

e. Ca and Cl

f. Na and P

Chapter 3 Notes

11

Covalent Bonds and MoleculesCovalent Bonds and Molecules• Covalent bonds form when two or more nonmetals

share their electrons. The electrons are at their lowest potential energy when they are between the two nuclei that are being joined:

Figure 3.2

12

Covalent Bonds and MoleculesCovalent Bonds and Molecules• Each atom in the bond “holds on” to the shared

electrons, and the atoms are thus physically tied together.

• When two or more atoms are joined by covalent bonds, the resulting structure is called a molecule.

• Molecular compounds are usually formed from combinations of nonmetals:– Nonmetal + Nonmetal → molecular compound– Hydrogen + Nonmetal → molecular compound

Chapter 3 Notes

13

Types of Chemical FormulasTypes of Chemical Formulas• An empirical formula gives the relative number of

atoms of each element in a compound; i.e., the smallest whole number ratio that is possible.

• A molecular formula gives the actual number of atoms of each element in a molecule of a compound.

Molecular Empiricalformula formula

Hydrogen peroxide H2O2 HOWater H2O H2OGlucose C6H12O6 CH2O

• A structural formula uses lines to represent covalent bonds, and shows how the atoms in a molecule are joined together:

H—O—O—H H—O—H O=C=O

14

Molecular ModelsMolecular Models• A ball-and-stick model represents atoms as balls

and covalent bonds as sticks; they are normally color-coded to specific elements, and show the three-dimensional relationships between atoms in a molecule.

• A space-filling molecular model shows the room taken up by the electron clouds in the molecule, and shows how the molecule might appear if it were scaled to a visible size.

Chapter 3 Notes

15

Representing MoleculesRepresenting Molecules

16

Atomic and Molecular ElementsAtomic and Molecular Elements• Atomic elements are found in nature in units of

single atoms. Most elements are atomic elements.• Molecular elements are found as molecules with

two or more of the same atom joined together.– Many nonmetals are found in their elemental

form as diatomic molecules (H2, N2, O2, F2, Cl2, Br2, I2); some as polyatomic molecules (P4, As4, S8, Se8)

Memorize!

Chapter 3 Notes

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Naming Chemical Naming Chemical CompoundsCompounds

18

MainMain--Group MetalsGroup Metals• Group 1A, 2A, and 3A metals tend to form cations

by losing all of their outermost (valence) electrons.

• The charge on the cation is the same as the group number.

• The cation is given the same name as the neutral metal atom, with the word “ion” added to the end.

aluminum ionbarium ionstrontium ioncalcium ionmagnesium ion

Ion name

Al3+

Ba2+

Sr2+

Ca2+

Mg2+

Ion

3A

2AGroup

cesium ionpotassium ionsodium ionlithium ionhydrogen ion

Ion name

Cs+

K+

Na+

Li+

H+

Ion1A

Group

Chapter 3 Notes

19

Transition and PostTransition and Post--Transition MetalsTransition Metals• These elements usually form ionic compounds;

many of them can form more than one cation.• The charges of the transition metals must be

memorized; Group 4A and 5A metal cations tend to be either the group number, or the group number minus two.)

• Common or trivial names: -ic endings go with the higher charge, -ous endings go with the lower charge [Fe2+ ferrous ion, Fe3+ ferric ion].

• Systematic names (Stock system): name the metal first, followed in parentheses by the charge in Roman numerals [Fe2+ iron(II) ion, Fe3+ iron(III) ion].

20

Transition and PostTransition and Post--Transition MetalsTransition Metals

cuprous ioncopper(I) ionCu+

cupric ioncopper(II) ionCu2+

cobaltous ioncobalt(II) ionCo2+

cobaltic ioncobalt(III) ionCo3+

ferrous ioniron(II) ionFe2+

ferric ioniron(III) ionFe3+

manganous ionmanganese(II) ionMn2+

manganic ionmanganese(III) ionMn3+

chromous ionchromium(II) ionCr2+

chromic ionchromium(III) ionCr3+

cadmium ionCd2+silver ionAg+zinc ionZn2+

nickel(II) ionNi2+

Common nameSystematic nameIon

Chapter 3 Notes

21

Transition and PostTransition and Post--Transition MetalsTransition Metals

gold(III) ionAu3+

bismuth(V) ionBi5+bismuth(III) ionBi3+

plumbic ionlead(IV) ionPb4+plumbous ionlead(II) ionPb2+stannic iontin(IV) ionSn4+stannous iontin(II) ionSn2+mercuric ionmercury(II) ionHg2+mercurous ionmercury(I) ionHg2

2+

Common nameSystematic nameIon

22

MainMain--Group NonmetalsGroup Nonmetals• Group 4A - 7A nonmetals form anions by gaining

enough electrons to fill their valence shell (eight electrons). The charge on the anion is the group number minus eight.

• The anion is named by taking the element stem and adding the ending -ide.

hydride ioniodide ionbromide ionchloride ionfluoride iontelluride ionselenide ionIon name

H–I–Br–Cl–F–Te2–Se2–Ion

1A

7A

6AGroup

sulfide ionoxide ionarsenide ionphosphide ionnitride ionsilicide ioncarbide ion

Ion name

S2–O2–As3–P3–N3–Si4–C4–Ion

6A

5A

4AGroup

Chapter 3 Notes

23

Common Cations and AnionsCommon Cations and AnionsIA VIIIA

1 2

1 H Elements To Memorize HeHydrogen Helium

1+, 1- IIA IIIA IVA VA VIA VIIA —3 4 6 Atomic Number 5 6 7 8 9 10

2 Li Be C Symbol B C N O F NeLithium Beryllium Carbon Name Boron Carbon Nitrogen Oxygen Fluorine Neon

1+ 2+ 4- Charges 3+ 4- 3- 2- 1- —11 12 13 14 15 16 17 18

3 Na Mg Al Si P S Cl ArSodium Magnesium VIII Aluminum Silicon Phosphorus Sulfur Chlorine Argon

1+ 2+ IIIB IVB VB VIB VIIB 644444474444448 IB IIB 3+ 4- 3- 2- 1- —19 20 24 25 26 27 28 29 30 33 34 35 36

4 K Ca Cr Mn Fe Co Ni Cu Zn As Se Br KrPotassium Calcium Chromium Manganese Iron Cobalt Nickel Copper Zinc Arsenic Selenium Bromine Krypton

1+ 2+ 2+, 3+ 2+, 3+ 2+, 3+ 2+, 3+ 2+ 1+, 2+ 2+ 3- 2- 1- —37 38 47 48 50 51 52 53 54

5 Rb Sr Ag Cd Sn Sb Te I XeRubidium Strontium Silver Cadmium Tin Antimony Tellurium Iodine Xenon

1+ 2+ 1+ 2+ 2+, 4+ 3+, 5+ 2- 1- —55 56 57 79 80 82 83 86

6 Cs Ba La Au Hg Pb Bi RnCesium Barium Lanthanum Gold Mercury Lead Bismuth Radon

1+ 2+ 3+ 1+, 2+ 2+, 4+ 3+, 5+ —88 89

7 Ra AcRadium Actinium

Lanthanides

92

Actinides UUranium

24

Polyatomic IonsPolyatomic Ions• Polyatomic ions are ions composed of groups of

covalently bonded atoms which have an overall charge.

phosphatePO43–perchlorateClO4

–

dichromateCr2O72–hypochloriteClO–

chromateCrO42–chloriteClO2

–

oxalateC2O42–chlorateClO3

–

thiosulfateS2O32–nitriteNO2

–

sulfiteSO32–nitrateNO3

–

sulfateSO42–cyanateOCN–

hydrogen carbonate, bicarbonateHCO3–cyanideCN–

carbonateCO32–hydroxideOH–

acetate (OAc–, CH3CO2–)C2H3O2

–hydroniumH3O+permanganateMnO4

–ammoniumNH4+

Chapter 3 Notes

25

Polyatomic Ions Polyatomic Ions —— Regularities in NamesRegularities in Names• There are some regularities in the names of these

polyatomic ions:• Thio- implies replacing an oxygen with a sulfur:

TeO42– tellurateIO3

– iodateSiO3

2– silicateAsO43– arsenateSeO4

2– selenateBrO3– bromate

CO32– carbonatePO4

3– phosphateSO42– sulfateClO3

– chlorateGroup 4AGroup 5AGroup 6AGroup 7A

• Replacing the first element with another element from the same group gives a polyatomic ion with the same charge, and a similar name:

SCN– thiocyanateS2O32– thiosulfate

OCN– cyanateSO42– sulfate

26

• Some nonmetals form a series of oxoanions having different numbers of oxygens (all with the same charge). The general rule for such series is shown below. (Note that in some cases, the -ate form has three oxygens, and in some cases four oxygens. These forms must be memorized.)

Polyatomic Ions Polyatomic Ions —— OxoanionsOxoanions

chlorideCl–stem + ide(the monatomic ion)

Xy–

perchlorateClO4–per + stem + ateXOn+1

y–

hypochloriteClO–hypo + stem + iteXOn-2y–

chloriteClO2–stem + iteXOn-1

y–

chlorateClO3–stem + ateXOn

y–

Chapter 3 Notes

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Polyatomic Ions Polyatomic Ions —— Ions Containing HydrogensIons Containing Hydrogens• Acid salts are ionic compounds that still contain an

acidic hydrogen, such as NaHSO4. In naming these salts, specify the number of acidic hydrogens still in the salt.

• The prefix bi- implies an acidic hydrogen.

dihydrogen phosphateH2PO4–

monohydrogen phosphateHPO42–

phosphatePO43–

hydrogen sulfate, bisulfateHSO4–

sulfateSO42–

hydrogen carbonate, bicarbonateHCO3–

carbonateCO32–

28

Writing Formulas of Ionic CompoundsWriting Formulas of Ionic Compounds• The positive ion is given first, followed by the

monatomic or polyatomic anion.• The subscripts in the formula must produce an

electrically neutral formula unit.• The subscripts should be the smallest set of whole

numbers possible.• If there is only one of a polyatomic ion in the

formula, do not place parentheses around it. If there is more than one of a polyatomic ion, put the ion in parentheses, and place the subscript after the parentheses.

• Remember the Prime Directive in writing formulas: Ca(OH)2 ≠ CaOH2!

Chapter 3 Notes

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Nomenclature of Ionic Compounds:Nomenclature of Ionic Compounds:Metal + NonmetalMetal + Nonmetal

• A binary compound is a compound formed from two different elements. A diatomic compound (or diatomic molecule) contains two atoms, which may or may not be the same.

• Metals combine with nonmetals to form ionic compounds. Name the cation first (specify the charge, if necessary), then the nonmetal anion (element stem + -ide).

• Do NOT use counting prefixes! This information is implied in the name of the compound.

name ofmetalcation

charge of metal cationin Roman numerals in

parenthesis (if necessary)

element stem ofnonmetal anion

+ -ide^

30

Nomenclature of Ionic Compounds:Nomenclature of Ionic Compounds:Metal + Polyatomic IonMetal + Polyatomic Ion

• Metals combine with polyatomic ions to give ionic compounds. Name the cation first (specify the charge, if necessary), then the polyatomic ion as listed in the previous table.

• Once again, do NOT use counting prefixes!

name ofmetalcation

charge of metal cationin Roman numerals in

parenthesis (if necessary)

name ofpolyatomic

ion^

Chapter 3 Notes

31

Nomenclature of Ionic Compounds: ExamplesNomenclature of Ionic Compounds: ExamplesNa+ Cl-

Na+ S2-

Na+ P3-

Ca2+ Cl-

Ca2+ S2-

Fe2+ Cl-

Fe3+ Cl-

Na+ SO42-

Ca2+ CO32-

Cr2+ NO3-

NaClNa2SNa3P

sodium chloridesodium sulfidesodium phosphide

32

Nomenclature of Ionic Compounds:Nomenclature of Ionic Compounds:HydratesHydrates

• Hydrates are ionic compounds which also contain a specific number of water molecules associated with each formula unit. The water molecules are called waters of hydration.

• The formula for the ionic compound is followed by a raised dot and #H2O — e.g., MgSO4·7H2O.

• They are named as ionic compounds, followed by a counting prefix and the word “hydrate”

copper(II) sulfate pentahydrateCuSO4·5H2Obarium chloride hexahydrateBaCl2·6H2Ocalcium sulfate hemihydrateCaSO4·½H2Omagnesium sulfate heptahydrate (Epsom salts)MgSO4·7H2O

Chapter 3 Notes

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Nomenclature of Binary Molecular CompoundsNomenclature of Binary Molecular Compounds• Two nonmetals combine to form a molecular or

covalent compound (i.e., one that is held together by covalent bonds, not ionic bonds).

• In many cases, two elements can combine in several ways to make completely different compounds (e.g., CO and CO2). It is necessary to specify how many of each element is present within the compound.

• In writing formulas, the more cation-like element (the one further to the left on the periodic table) is placed first, then the more anion-like element (the one further to the right on the periodic table).• Important exception: halogens are written before

oxygen. For two elements in the same group, the one with the higher period number is placed first.

34

Nomenclature of Binary Molecular CompoundsNomenclature of Binary Molecular Compounds• The first element in the formula is given the element

name, and the second one is named by replacing the ending of the element name with -ide.

• A numerical prefix is used in front of each element name to indicate how many of that element is present. (If there is only one of the first element in the formula, the mono- prefix is dropped.)

deca-10

nona-octa-hepta-

987

hexa-penta-tetra-

654

tri-3di-2mono-1

prefix(omit mono)

name of first

element

stem of 2nd

element+ -ide

prefix

^

Chapter 3 Notes

35

Nomenclature of Binary Molecular CompoundsNomenclature of Binary Molecular CompoundsNO nitrogen monoxideNO2 nitrogen dioxideN2O dinitrogen monoxideN2O3 dinitrogen trioxideN2O4 dinitrogen tetroxideN2O5 dinitrogen pentoxide

• Some molecular compounds are known by common or trivial names:

H2O waterNH3 ammonia

36

• Acids are compounds in which the “cation” is H+. These are often given special “acid names” derived by omitting the word “hydrogen,” adding the word “acid” at the end, and changing the compound suffix as shown below:

Nomenclature of AcidsNomenclature of Acids

hydro + stem + ic acidstem + idestem + ous acidstem + itestem + ic acidstem + ate

Acid nameCompound name

hydrochloric acidchlorous acidsulfuric acidchloric acid

hydrogen chlorideHClhydrogen chloriteHClO2

hydrogen sulfateH2SO4

hydrogen chlorateHClO3

oxyacids

binary acids

Chapter 3 Notes

37

Summary of Chemical NomenclatureSummary of Chemical Nomenclature

38

Chapter 3 Notes

39

Examples: Formulas and NomenclatureExamples: Formulas and Nomenclature2. Write the formula for the ionic compound formed

between the following pairs of species and provide a name for the compound.

a. Na and sulfate

b. Ammonium and nitrate

c. Ammonium and sulfate

d. Zn and Cl

e. Mercury(I) and nitrite

f. Mercury(II) and sulfite

g. Chromium and S

40

Examples: Formulas and NomenclatureExamples: Formulas and Nomenclature3. Name the following compounds.

a. Ca(NO3)2

b. BaCO3

c. SO3

d. SnCl4

e. Fe2(CO3)3

f. AlPO4

g. N2O

Chapter 3 Notes

41

Examples: Formulas and NomenclatureExamples: Formulas and Nomenclature4. Name the following compounds.

a. CrO

b. Mn2O3

c. KHSO4

d. H2SO3

e. PBr3

f. HCl

g. HClO2

42

Examples: Formulas and NomenclatureExamples: Formulas and Nomenclature5. Write formulas for the following compounds.

a. sodium nitrite

b. lithium hydroxide

c. barium chlorate

d. potassium perchlorate

e. chloric acid

f. magnesium phosphate

g. iron(II) carbonate

Chapter 3 Notes

43

Examples: Formulas and NomenclatureExamples: Formulas and Nomenclature6. Write formulas for the following compounds.

a. calcium bicarbonate

b. periodic acid

c. silver chromate

d. diphosphorus pentoxide

e. manganese(III) carbonate

f. potassium hypochlorite

g. hydrofluoric acid

44

Examples: Formulas and NomenclatureExamples: Formulas and Nomenclature7. Which of the following formulas and/or names is

written incorrectly?

a. NaSO4

b. Na2Cl

c. MgNO3

d. magnesium dichloride

e. iron(III) phosphate, Fe3(PO4)2

f. tin(IV) sulfate, Sn(SO4)2

g. nitrogen chloride, NCl3

Chapter 3 Notes

45

Percent Percent Composition, Composition,

Empirical Formulas, Empirical Formulas, and and

Elemental AnalysisElemental Analysis

46

Percent Composition and Mass PercentagePercent Composition and Mass Percentage• The percent composition of a compound is a list of

the elements present in a substance listed by mass percent. Knowing the percent composition is often a first step to determining the formula of an unknown compound.

• The mass percentage (mass %) of an element in the compound is the portion of the compound’s mass contributed by that element, expressed as a percentage:

100 compound of massmolar

X of massmolar formulain X of atoms Xelement of % Mass ××

=

Chapter 3 Notes

47

Percent Composition and Mass PercentagePercent Composition and Mass Percentage• What is the mass percentage of Cl in the chloro-

fluorocarbon CCl2F2 (Freon-12)?

Mass % of Cl = 2 × atomic mass of Clmolar mass of CCl2F2

× 100

= 2 × 35.453 g/mol120.91 g/mol × 100

= 58.64%• The mass percentage can be used as a conversion

factor between the mass of the element and the mass of the compound.

58.64 g Cl : 100 g CCl2F2

22FCCl g 100Cl g 64.58

Cl g 64.58FCCl g 100 22

48

Examples: Mass PercentageExamples: Mass Percentage8. Glucose, or blood sugar, has the molecular formula

C6H12O6.a. What is the percent composition of glucose?b. How many grams of carbon are in 39.0 g of

glucose (the amount of sugar in a typical soft drink)?

Answer: a) 40.00% C, 6.714% H, 53.29% Ob) 15.6 g C

Chapter 3 Notes

49

Examples: Mass PercentageExamples: Mass Percentage9. The U.S. Food and Drug Administration (FDA)

recommends that you consume less than 2.4 g of sodium per day. What mass of sodium chloride in grams can you consume and still be within the FDA guidelines? (similar to Example 3.14)

Answer: 6.1 g NaCl

50

Conversion Factors from Chemical FormulasConversion Factors from Chemical Formulas• Another way to approach a problem like the

previous two is to use the atom ratios in the formulas as mole ratios:

• Using conversion factors like this, it is possible to convert from grams of CCl2F2 to moles of CCl2F2, then use the ratio of atoms of Cl in CCl2F2 to convert to moles of Cl, and finally use the molar mass of Cl to convert to grams of Cl.

58.64 g Cl : 100 g CCl2F2

1 mol CCl2F2 : 2 mol Cl

Chapter 3 Notes

51

Examples: Chemical Conversion FactorsExamples: Chemical Conversion Factors8b. Glucose, or blood sugar, has the molecular

formula C6H12O6. How many grams of carbon are in 39.0 g of glucose (the amount of sugar in a typical soft drink)?

39.0 g C6H12O61 mol C6H12O6

180.16 g C6H12O6×

6 mol C1 mol C6H12O6

×12.01115 g C

1 mol C= 15.6 g C

×

52

Examples: Mass PercentageExamples: Mass Percentage10. What mass of hydrogen (in grams) is contained in

1.00 gallons of water? (The density of water is 1.00 g/mL) (Example 3.14)

Answer: 423 g H

Chapter 3 Notes

53

Empirical Formula from Mass PercentageEmpirical Formula from Mass Percentage• We can also go the other way around, and use the

percent composition of a substance to find first its empirical formula, and then its molecular formula.

• If by some process we determine the percent composition of an unknown compound, we can convert this into a gram ratio by assuming that we have 100 g of the compound, and then to a mole ratio by using the atomic weights:

Sample: 84.1% C, 15.9% HAssume 100 g of sample:

C mol 7.00 C g 12.01115

C mol 1 C g 1.84 =×

H mol 15.8 H g 1.00797

H mol 1 H g 5.91 =×

54

Empirical Formula from Mass PercentageEmpirical Formula from Mass Percentage• Since atoms combine in the same ratio that moles

do, we divide all of the numbers of moles by the smallest number to put everything into lowest terms:

2.261.007.0015.8

7.007.00

numbersmallest by divide15.87.00 HC HC HC →⎯⎯⎯⎯⎯⎯ →⎯

• If the mole ratio is not all whole numbers, we multiply through by the smallest integer which will turn all of the numbers into integers. These numbers are the subscripts of the elements in the empirical formula.

( ) formula) (empirical HC HC HC 949.044.0042.261.00 →→

Chapter 3 Notes

55

Molecular Formula from Empirical FormulaMolecular Formula from Empirical Formula• If we know the molar mass of the compound, we can

obtain the molecular formula by dividing the weight of the empirical formula into the molar mass; this will determine the number of empirical formula units in the molecule.

4.000 g/mol 57.12g/mol 228.48

weightformula empiricalweightmolecular

=→

Suppose the molecular weight of the substance is found to be 228.48 g/mol:

( ) formula) (molecular HC HC 3616494 →

56

Examples: Empirical & Molecular FormulasExamples: Empirical & Molecular Formulas11. Vitamin C (ascorbic acid) contains 40.92% C,

4.58% H, and 54.50% O by mass. What is the empirical formula of ascorbic acid? (sim. to Example 3.17)

Answer: C3H4O3

Chapter 3 Notes

57

Examples: Empirical & Molecular FormulasExamples: Empirical & Molecular Formulas12. Black iron oxide is an ore containing iron and

oxygen that occurs in magnetite. A 2.4480 g sample of the ore is found to contain 1.7714 g of iron. Calculate the empirical formula of black iron oxide.

Answer: Fe3O4

58

Examples: Empirical & Molecular FormulasExamples: Empirical & Molecular Formulas13. Styrofoam is a polymer made from the monomer

styrene. Elemental analysis of styrene shows its percent composition to be 92.26 % C and 7.75% H. Its molecular mass is found to be 104.15 g/mol. What are the empirical and molecular formulas of styrene?

Answer: empirical = CH, molecular = C8H8

Chapter 3 Notes

59

Examples: Empirical & Molecular FormulasExamples: Empirical & Molecular Formulas14. Butanedione is a main component in the smell and

taste of butter and cheese. The empirical formula of butanedione is C2H3O and its molar mass is 86.09 g/mol. What is its molecular formula? (Example 3.18)

Answer: C4H6O2

60

Elemental / Combustion AnalysisElemental / Combustion Analysis• One common way of obtaining a chemical formula

is by performing a combustion analysis (a specific type of elemental analysis).

• In this technique, an unknown sample is burned in pure O2 (a combustion reaction), which converts all of the carbon atoms in the sample into CO2 and all of the hydrogen atoms into H2O.

C, H, O + O2 → CO2 + H2O

Figure 3.9

Chapter 3 Notes

61

Elemental / Combustion AnalysisElemental / Combustion Analysis• The masses of CO2 and H2O are measured after the

process is complete, and from this data, the amount of carbon and hydrogen in the original sample can be determined.

• Elements besides C and H must be determined by other methods; O is usually found by difference.

C % sample in C g C mol CO mol CO g 22 →→→→

H% sample in H g H mol O Hmol O Hg 22 →→→→

H)% C (% - 100% O % +=

62

Examples: Combustion AnalysisExamples: Combustion Analysis15. A sample of an unknown compound with a mass of

0.5438 g is burned in a combustion analysis. The mass of CO2 produced was 1.039 g and the mass of H2O was 0.6369 g. What is the empirical formula of the compound? (sim. to Examples 3.19 & 3.20)

Answer: C2H6O

Chapter 3 Notes

63

Molecules and IsomersMolecules and Isomers• Even knowing the empirical or molecular formulas

of a compound does not necessarily tell us what that compound actually is.

• We’ve already seen that the empirical formula only tells us about the relative numbers of atoms present within the formula unit or molecule.

• Many different compounds can have the same empirical formula. For instance, there are dozens of different compounds that have the empirical formula CH2O.– Notice that in on the following slide, there is no

relationship between the structure and how many ‘CH2O’ units the molecule contains.

64

Some Compounds with Empirical Formula CHSome Compounds with Empirical Formula CH22OO• Composition by mass 40.0% C, 6.71% H, 53.3% O

Major nutrient for energy in cells180.166C6H12O6Glucose

Component of ribonucleic acid (RNA); found in vitamin B2

150.135C5H10O5Ribose

Forms during sugar metabolism120.104C4H8O4Erythrose

Found in sour milk and sourdough bread; forms in muscles during exercise90.083C3H6O3Lactic acid

Vinegar (5% solution); acetate polymers60.052C2H4O2Acetic acid

Disinfectant; biological preservative30.031CH2OFormaldehyde

Function

Molar Mass

(g/mol)

No. of ‘CH2O’

UnitsMolecular FormulaName

Chapter 3 Notes

65

Structural IsomersStructural Isomers• Even compounds that have the same molecular

formula can have the atoms connected in a different order — these are structural isomers.

C

H

H

CH

H

H

O H C

H

H

OH C H

H

H

RefrigerantIntoxicantFunction0.00195 g/mL0.789 g/mLDensity (at 20°C)

-25°C78.5°CBoiling point-139°C-117°CMelting point

Colorless gasColorless liquidAppearance46.0746.07Molar Mass (g/mol)

C2H6OC2H6OMolecular Formula

Dimethyl etherEthanol

66

Mass SpectroscopyMass Spectroscopy• A mass spectrometer is a device which is often

used to obtain atomic and molecular masses. A sample is vaporized in an evacuated chamber, ionized, accelerated by an electrical field, and passed through the poles of a strong magnet, which deflects the ionized particles towards a detector.

• Lighter ions are deflected more than heavier ions, and the detector measures the mass of the particles, and counts the number of particles with that mass.

• The resulting mass spectrum is a graph of ion mass vs. relative number of ions produced.

• Modern mass spectrometers can measure molecular masses and even percent compositions to very high precisions, and the fragmentation pattern of the ions can reveal a great deal about molecular structure.

Chapter 3 Notes

67

Mass SpectroscopyMass Spectroscopy

Mass spectrometer

Mass spectrum of naphthalene (C10H8)

68

Chapter 3 Notes

69

Chemical ReactionsChemical Reactions

70

Chemical Reactions and Chemical EquationsChemical Reactions and Chemical Equations• A chemical reaction occurs when atoms of different

elements combine and create a new chemical compound, with properties which may be completely unlike those of its constituent elements.

• A chemical reaction is written in a standard format called a chemical equation. The reactants (starting materials) are written on the left, and the productson the right, with an arrow in between to indicate a transformation.

• Equations are the “sentences” of chemistry, just as formulas are the “words” and atomic symbols are the “letters.”

Zn + S ⎯⎯→ ZnSreactants products

Chapter 3 Notes

71

A Chemical Reaction IllustratedA Chemical Reaction Illustrated

Sodium Chloride (NaCl)solid

mp 801°Cbp 1413°C

white crystals or powderpleasant taste

conducts electricity when dissolved in water

dissolves freely in water

⎯→Chlorine (Cl2)gas

mp -101°Cbp -34°C

pale, yellow-green gaspoisonous; causes lung damage

does not conduct electricitydissolves slightly in water

+Sodium (Na)solid

mp 97.8°Cbp 881.4°C

silvery metallic surfacesoft, easily cut

conducts electricityreacts violently with water

2Na + Cl2 → 2NaCl

72

Balancing Chemical ReactionsBalancing Chemical Reactions• A chemical equation must be balanced: the kinds

and numbers of atoms must be the same on both sides of the reaction arrow (conservation of mass).

unbalanced: H2 + O2 → H2Owrong equation: H2 + O2 → H2O2

balanced: H2 + ½O2 → H2Obalanced: 2H2 + O2 → 2H2O

Chapter 3 Notes

73

Balancing Chemical ReactionsBalancing Chemical Reactions• Equations are balanced by placing a stoichiometric

coefficient in front of each species, indicating how many units of each compound participate in the reaction.– If no coefficient is present, it is assumed to be 1.– Usually, we use the smallest whole-number ratios

for the coefficients.– Never balance equations by changing subscripts!

This changes the identity of the species involved in the reaction!

– In general, it’s a good idea to balance the atoms in the most complex substances first, and the atoms in the simpler substances last.

74

Examples: Balancing EquationsExamples: Balancing Equations__ C4H10 + __ O2 → __ CO2 + __ H2O

__ C(s) + __ O2(g) → __ CO2(g)

__ Fe2O3(s) + __ C(s) → __ Fe(s) + __ CO2(g)

__ HCl(aq) + __ CaCO3(s) → __ CaCl2(aq) + __ H2O(l) + __ CO2(g)

__ Al(NO3)3 + __ CaSO4 → __ Al2(SO4)3 + __ Ca(NO3)2

__KClO3 + __C12H22O11 → __KCl + __CO2 + __H2O

16.

Chapter 3 Notes

75

What Do Coefficients Mean?What Do Coefficients Mean?• On the microscopic level, the coefficients and

chemical symbols in a balanced equation represent the behavior of individual atoms and molecules:

2 molecules H2 + 1 molecule O2 → 2 molecules H2O

• On the macroscopic level, since moles combine in the same ratios that atoms do, the coefficient can also be interpreted as 2 moles of H2 reacting with 1 mole of O2 to form 2 moles of H2O.

76

Chapter 3 Notes

77

Organic CompoundsOrganic Compounds

78

Organic Compounds and Organic ChemistryOrganic Compounds and Organic Chemistry• Originally, “organic compounds” were compounds

that were obtained only from living organisms (like sugar), in contrast to “inorganic compounds,” which came from the earth (like salt). It was believed that only living organisms possessed the “vital force”necessary to create organic compounds (“vitalism”).

• Eventually, it was realized that organic substances followed the same rules of chemistry that inorganic substances did, and could be synthesized in the lab and manipulated just like inorganic compounds.

• Now, organic compounds are defined as compounds that contain the element carbon, and organic chemistry is the study of compounds of carbon.

Chapter 3 Notes

79

WhatWhat’’s So Great About Carbon?s So Great About Carbon?• Carbons atoms can be linked by strong, stable

covalent bonds.

C

neutral carbon, C

C

carbon cation, C4+

C

carbide anion, C4-

CH H

H

H

C

H

H

HH

80

WhatWhat’’s So Great About Carbon?s So Great About Carbon?• Carbon atoms can form stable bonds to many other

elements (H, F, Cl, Br, I, O, N, S, P, etc.). Most organic compounds contain a few hydrogens, and sometimes oxygen, nitrogen, sulfur, phosphorus, etc.

• Carbon atoms can form complex structures, such as long chains, branched chains, rings, chiralcompounds (having a particular “handedness”), complex 3D shapes, etc.

• Because of this variety in bonding and complexity, carbon atoms can form a tremendous variety of compounds. More than 16,000,000 organic compounds are known, as opposed to about 600,000 inorganic compounds.

Chapter 3 Notes

81

WhatWhat’’s So Great About Carbon?s So Great About Carbon?• Complex organic compounds can perform a number

of useful biological functions (vitamins, carbohydrates, lipids, proteins, enzymes, ATP, DNA, RNA are all organic compounds) which are studied in biochemistry.

• Complex organic compounds are present in the foodswe eat (carbohydrates, proteins, fats, etc.)

• Most medicines, whether they come from a chemical plant or a green plant, are organic compounds.

• Most fuels are organic compounds (wood, coal, natural gas, gasoline, kerosene, diesel fuel, oil, and other petroleum-based products).

• Complex organic compounds are also useful in technology (paints, plastics, rubber, textiles, etc.).

82

HydrocarbonsHydrocarbons• Organic compounds can be classified by regular

groupings of atoms called functional groups.• Hydrocarbons contain only carbon and hydrogen.

They are derived primarily from petroleum sources, and are frequently burned as fuel (gasoline, diesel):– Alkanes contain carbon-carbon single bonds.– Alkenes contain carbon-carbon double bonds.– Alkynes contain carbon-carbon triple bonds.

CH H

H

H

methanethe major component of

natural gas

C CH C

H

H

H

H

H

H

H

propaneused in outdoor cooking fuels

C CH C

H

H

H

H

C

H

H

butaneused in lighter fluids

H

H

H

C CH C

H

H

H

C

H

H

H

2-methylpropane(isobutane)

H

HH

Chapter 3 Notes

83

HydrocarbonsHydrocarbons

C CH C

H

H

H

H

C

H

H

C C C C H

H H H H H

HHHHH

octanea component of gasoline

C C

H

H H

Hethene

(ethylene)a ripening agent in some

fruits; used in the manufacture of plastics

H C C Hethyne

(acetylene)used in welding torches

CF F

Cl

Cl

dichlorodifluoromethane(Freon-12)

a chlorofluorocarbon formerly used as an aerosol propellant and

refrigerant

C

CC

C

CC

H

H

H

H

H

H

benzenea common

industrial solvent

H2C

H2CCH2

CH2

CH2

H2C

cyclohexane

84

Organic Compounds Containing OxygenOrganic Compounds Containing Oxygen• Other organic compounds contain oxygen atoms:

– Alcohols contain an —OH group bonded to a carbon atom.

– Aldehydes and ketones contain carbon-oxygen double bonds.

– Carboxylic acids and esters contain carbons that are double-bonded to one oxygen and single-bonded to another.

H3C CH2 O Hethanol

(ethyl alcohol)alcohol found in

fermented beverages

H3C CH

CH3

OH

2-propanol(isopropyl alcohol)found in rubbing

alcohol

H C

O

Hmethanal

(formaldehyde)an aldehyde

a preservative; foundin wood smoke

H3C C

O

Hethanal

(acetaldehyde)an aldehyde

found in perfumes and flavors; metabolic product of

alcohol consumption

Chapter 3 Notes

85

Organic Compounds Containing OxygenOrganic Compounds Containing Oxygen

H3C C

O

CH32-propanone

(acetone)a ketone

common organic solvent;used in paint thinners and

fingernail polishes

CC

H

OHC

HC

HCCH

CH

benzaldehydean aldehyde

causes the odor of almonds and cherries; also found in

apricots and peaches

H3C C

O

OHethanoic acid(acetic acid)

a carboxylic acidproduced in the oxidation of ethanol; active ingredient in vinegar (French, vin aigre,

"sour wine")

C

O

butanoic acid(butyric acid, from Latin butyrum, butter)

a carboxylic acidproduced from the breakdown of soft

triglycerides in butter; has a foul, rancid odor

CH3CH2CH2 OH H3C C

O

Oethyl ethanoate(ethyl acetate)

an esterfound in glues and fingernail

polish removers

CH2CH3

HO

CH3O CH

Vanillinflavoring in Vanilla beans

O

86

Organic Compounds Containing NitrogenOrganic Compounds Containing Nitrogen• Other organic compounds contain nitrogen atoms:

– Amines contain carbon-nitrogen single bonds.– Amides contain nitrogen atoms connected to

carbon-oxygen double bonds.– Amino acids contain both amine and carboxylic

acid groups, and are linked together by amide bonds to form proteins.

NH CH2CH3

H

ethylaminean amine

smell of rotten fish

NH3C CH3

CH3

trimethylaminean amine

smell of rotten fish

C

O

ureaan amide

the major organic component of urine;

about 25 g are excretedevery day

H2N NH2 CC OH

O

H2N

H

CH3alanine

an amino acidused in the synthesis

of proteins

Chapter 3 Notes

87

Other Organic MoleculesOther Organic Molecules

H

C

C OH

Glucosea carbohydrate

the metabolism of glucose is a major source of energy for living organisms

C

C

C

CH2OH

HHO

OHH

OHH

H O

O

H

HO

H

HO

H

HOHH

OH

OH

Vitamin C (ascorbic acid)a water-soluble vitamin found in citrus fruits; prevents scurvy; essential for healthy blood

vessels, bones, and teeth; helps form collagen, a protein that holds tissues together

CC

CO

C

HO OH

OCHCH2OH

OH

H

N

NC

CC

N

CH

N

O

CH3

O

CH3

CH3

Caffeinea mild stimulant found in the

seeds of Coffea arabica, roasted coffee beans

CH3O

HO

N

O

HCapsaicin

responsible for the hot taste of red and green chili peppers

88

Other Organic MoleculesOther Organic MoleculesCH3

CH3

CH3

OH

CH3 CH3

Vitamin A3,7-Dimethyl-9-(2,6,6-trimethyl-1-cyclohex-1-enyl)

-2,4,6,8-nonatetraen-1-olA fat-soluble vitamin; a metabolic product of

carotene, found in liver, egg yolks, butter, and milk;combines with the protein opsin to form rhodopsin,the primary light-gathering pigment in vertebrate

retinas; also involved in cell growth and maintenance of healthy skin tissue.

O

HO

HO

N

CH3

Morphinefound in the opium poppy; a CNS

depressant; very effective painkiller

COH

O

OHSalicylic acid

found in the bark of the willow tree (Salix); reduces fever and relives pain and inflammation,

but causes irritation of the mucous membranes, ulcers, and

stomach bleeding

COH

O

O C

O

CH3Aspirin (acetylsalicylic acid)

produced by reacting salicylic acidwith acetic anhydride, giving a

compound which does not cause asmuch irritation, but retains all of the beneficial medical properties

N

OO

H

H

H

H

H N

Strychninea poison from strychnos plant

(Nux vomica); used as a rat and mouse poison

Chapter 3 Notes

89

Families of Organic CompoundsFamilies of Organic Compounds

90

Organic chemistry nowadays almost drives me mad. To me it appears like a primeval tropical forest full of the most remarkable things, a dreadful endless jungle into which one does not dare enter, for there seems to be no way out.

Friedrich Wöhler