1 molecules and compounds read chapter 3. study all examples and complete all exercises. complete...

1

Molecules and CompoundsMolecules and CompoundsRead Chapter 3.

Study all examples and complete all exercises.

Complete all bold numbered problems.

2

Chapter 3 OutlineChapter 3 Outline

• Molecular FormulaMolecular Formula

• Molar MassMolar Mass

• Empirical and Molecular Empirical and Molecular FormulaFormula

• NomenclatureNomenclature

3

Compounds & MoleculesCompounds & Molecules

NaCl, salt

Buckyball, C60

4

Compounds & MoleculesCompounds & Molecules

• COMPOUNDS COMPOUNDS are a combination of 2 or

more elements in definite ratios by mass.

• The character of each element is lost when

forming a compound.

• MOLECULES MOLECULES are the smallest unit of a smallest unit of a

compound that retains the characteristics of compound that retains the characteristics of

the compound. the compound.

5

MOLECULAR FORMULASMOLECULAR FORMULAS• Formula for glycine isFormula for glycine is CC22HH55NNOO22• In one molecule there areIn one molecule there are

– 2 C 2 C atomsatoms

– 5 H5 H atomsatoms

– 1 N1 N atomatom

– 2 O2 O atomsatoms

6

WRITING FORMULASWRITING FORMULAS

• FormulaFormula

HOCHHOCH22CHCH22OHOH

to show atom orderingto show atom ordering

• or in the form of a or in the form of a structural formulastructural formula

7

Molecular ModelingMolecular Modeling

8

Molecular ModelingMolecular Modeling

Ball & stickBall & stick Space-fillingSpace-filling

Drawing of glycineDrawing of glycineCC

HH

HH CC

HH

HH

OO

OO HHNN

9

Resources for Resources for Molecular ModelingMolecular Modeling

• Oxford Molecular/CAChe Scientific Oxford Molecular/CAChe Scientific

software on Saunders General software on Saunders General

Chemistry CD-ROMChemistry CD-ROM

• Rasmol and Chime on the InternetRasmol and Chime on the Internet

• See http://www.saundercollege.comSee http://www.saundercollege.com

10

ELEMENTS THAT EXIST ELEMENTS THAT EXIST AS MOLECULESAS MOLECULES

Allotrope of Allotrope of CC

BuckyballBuckyball, CC6060

12

IONS AND IONIC COMPOUNDSIONS AND IONIC COMPOUNDS

• IONS IONS are atoms or groups of atoms are atoms or groups of atoms

with a positive or negative charge. with a positive or negative charge.

• Taking away an electron from an atom Taking away an electron from an atom

gives a gives a CATION with a positive CATION with a positive

charge.charge.

• Adding an electron to an atom gives an Adding an electron to an atom gives an

ANION with a negative charge.ANION with a negative charge.

13Formation of Formation of Cations & AnionsCations & Anions

14

Formation of Formation of Cations & AnionsCations & Anions

A cation forms when an atom loses one or more electrons.

An anion forms when an atom gains one or more electrons

Mg --> MgMg --> Mg2+2+ + 2 e- + 2 e- F + eF + e-- --> F --> F--

15

PREDICTING ION CHARGESPREDICTING ION CHARGES

In generalIn general

• metals (Mg) metals (Mg) lose electrons lose electrons ---> ---> cationscations

• nonmetals (F) nonmetals (F) gain electronsgain electrons ---> ---> anionsanions

LiLi1+1+ F F1-1- LiF LiF

MONATOMIC IONSMONATOMIC IONS

16

Figure 3.7

Sn4+Pb4+

Also

17

METALSMETALSM ---> n e- + MM ---> n e- + Mn+n+

where n = periodic groupwhere n = periodic group

NaNa++

MgMg2+2+

AlAl3+3+

Transition metals --> MTransition metals --> M2+2+ or M or M3+3+

are most commonare most common

18

NONMETALSNONMETALS

NONMETAL + n e- ------> XNONMETAL + n e- ------> Xn-n-

where n = 8 where n = 8 - - Group numberGroup number

CC4-4- carbidecarbide

NN3-3- nitridenitride

OO2-2- oxideoxide

FF-- fluoridefluoride

BromineBromine

19

Groups of atoms with a charge.

(See back of periodic chart)

POLYATOMIC IONSPOLYATOMIC IONS

20

Some Common Some Common Polyatomic IonsPolyatomic Ions

HHNNOO33

nitric acidnitric acid

NNOO33--

nitrate ionnitrate ion

21


NNHH44++

ammonium ionammonium ion

One of the few common One of the few common polyatomic cationspolyatomic cations

22Some Common Some Common Polyatomic IonsPolyatomic Ions

COCO332-2-

carbonate ion

HCOHCO33--

bicarbonate ion

hydrogen carbonate

23Some Common Some Common Polyatomic IonsPolyatomic Ions

POPO443-3-

phosphate ion

CHCH33COCO22--

acetate ion

24

SOSO442-2-

Sulfate ion

SOSO332-2-

Sulfite ion


25

NONO33--

Nitrate ion

NONO22--

Nitrite ion


26

COMPOUNDS FORMED FROM COMPOUNDS FORMED FROM IONSIONS

CATION + ANION CATION + ANION COMPOUNDCOMPOUND

NaNa++ + Cl + Cl-- NaClNaCl

A neutral compound requires equal number of + and - charges.

27

IONIC COMPOUNDSIONIC COMPOUNDS

NNHH44++

ClCl--

ammonium chloride,ammonium chloride, NHNH44ClCl

28

Some Ionic CompoundsSome Ionic CompoundsCaCa2+2+ + 2 F + 2 F-- CaF CaF22

Calcium fluoride

MgMg2+2+ + 2 NO + 2 NO33-- Mg(NO Mg(NO33))22

Magnesium nitrate

3 Fe3 Fe2+2+ + 2 PO + 2 PO443-3- Fe Fe33(PO(PO44))22

Iron(II) phosphate

Calcium FluorideCalcium Fluoride

29

Sample QuestionsSample Questions• Predict the charges for the ions formed

from:SeSe GaGa

PP SrSr

• Give the formula for each ion in Al2(SO4)3

• Give the formula for the ionic compound

that forms between Na and SNa and S

Ga and OGa and O

Ba and NBa and N

Answers

30

Properties of Ionic CompoundsProperties of Ionic CompoundsForming NaCl from Na and ClForming NaCl from Na and Cl22

• A metal atom can transfer an electron to a nonmetal.

• The resulting cation and anion are attracted to each other by

electrostatic electrostatic forcesforces..

3030

31

Electrostatic ForcesElectrostatic Forces

The oppositely charged ions in ionic compounds are attracted to one another by

ELECTROSTATIC FORCESELECTROSTATIC FORCES..

These forces are governed by

COULOMB’S LAWCOULOMB’S LAW..

32

Electrostatic ForcesElectrostatic ForcesCOULOMB’S LAWCOULOMB’S LAW

As ion charge increases, the attractive force _______________.

As the distance between ions increases, the attractive force ________________.

This idea is important and will come up many times in future

discussions!

Force of attractionForce of attraction Force of attractionForce of attraction ==== (charge on(charge on++)(charge on)(charge on--))(charge on(charge on++)(charge on)(charge on--))

(distance between ions)(distance between ions)22(distance between ions)(distance between ions)22

33

Importance of Coulomb’s LawImportance of Coulomb’s Law

NaNaClCl,, NaNa++ and and ClCl--,,m.p. 801 m.p. 801 ooCC

MgMgOO,, MgMg2+2+ andand OO2-2-

m.p. 2800 m.p. 2800 ooCC

AlN, AlAlN, Al3+3+ and N and N3-3- m.p. 2900 m.p. 2900 ooCC

34

Names of CompoundsNames of Compounds

• Rules for nomenclature are Rules for nomenclature are found in section 3.5 found in section 3.5

• STUDY them carefully!!STUDY them carefully!!

• We will be studying We will be studying nomenclature in the nomenclature in the laboratory in Experiment MA.laboratory in Experiment MA.

35

Counting AtomsCounting Atoms• Mg burns in air (Mg burns in air (OO22) to) to

produce white produce white magnesium oxide,magnesium oxide, MgMgOO.. • How can we figure out How can we figure out

how much oxide is how much oxide is produced from a produced from a given mass ofgiven mass of MgMg??

36

Counting AtomsCounting Atoms

• Chemistry is a quantitative science — we need a “counting unit.”

• The MOLEThe MOLE

• 1 mole is the amount of substance that contains as many particles (atoms, molecules) as there are in 12.0 g of 12C.

37

Particles in a MoleParticles in a Mole

6.02 x 106.02 x 102323

Avogadro’s Number

Amedeo Avogadro1776-1856

There is Avogadro’s number of There is Avogadro’s number of particles in a mole of any substance.particles in a mole of any substance.

38

MoleMole in Chemistry is NOT:in Chemistry is NOT:

•An informer / spyAn informer / spy

•Dark spot on Cindy Crawford’s upper lipDark spot on Cindy Crawford’s upper lip

•Rodent that burrows in the groundRodent that burrows in the ground

•A tunneling machineA tunneling machine

•Wave breakWave break

•Spicy Mexican sauceSpicy Mexican sauce

•An informer / spyAn informer / spy

•Dark spot on Cindy Crawford’s upper lipDark spot on Cindy Crawford’s upper lip

•Rodent that burrows in the groundRodent that burrows in the ground

•A tunneling machineA tunneling machine

•Wave breakWave break

•Spicy Mexican sauceSpicy Mexican sauce

39

A mole is a convenient A mole is a convenient measuring tool.measuring tool.

Pair Dozen Ream

Baseballs 2 baseballs 12 baseballs 13 baseballs500 baseballs

Pineapples2 Pineapples

12 Pineapples

13 Pineapples500 Pineapples

Calculators2 Calculators

12 Calculators

13 Calculators500 Calculators

Planets 2 Planets 12 Planets 13 Planets 500 Planets

40

Mole = mol = Mole = mol = 6.022 6.022 10 102323 “particles” “particles”

Mole

Baseballs 6.022 1023 baseballs

Pineapples 6.022 1023 Pineapples

Calculators 6.022 1023 Calculators

Planets 6.022 1023 Planets

41

Just as

1 doz eggs = 12 eggs

or

1 mol of eggs = 6.022 1023 eggs

A mole is a “Number”

1 mol of H = 6.022 1023 atoms of H

1 mol of O = 6.022 1023 atoms of O

1 mol of Al = 6.022 1023 atoms of Al

1 mol of Cr = 6.022 1023 atoms of Cr

42

In chemistry, the In chemistry, the molmol is is more then just a numbermore then just a number

1 mol 1 mol amu = 1.00 g amu = 1.00 g

12 2411 1.661 10

12amu mass C g

43

1 mol 1 mol amu = 1.00 g amu = 1.00 gProof:

1 mol = 6.022 1023

amu = 1.661 10-24 g

1 mol amu = (6.022 1023) (1.661 10-24g) = 1.00 g

44

Molar MassMolar Mass1 mol of 12C

= 12.00 g of C= 6.02 x 1023 atoms of C

12.00 g of 12C is its

MOLAR MASSTaking into account all

of the isotopes of C, the molar mass of C is 12.011 g/mol

45

Molar MassMolar Mass1 mol of 12C = 12.00 g of C

= 6.02 x 1023 atoms of C

12.00 g of 12C is its MOLAR MASS

Taking into account all of the isotopes of

C, the molar mass of C is 12.011 g/mol

Find molar mass from periodic table

1313

AlAl

26.981526.9815

atomic numberatomic number

symbolsymbol

atomic weightatomic weight

46

PROBLEM: How many moles PROBLEM: How many moles are represented by 0.200 g of are represented by 0.200 g of Mg?Mg?

How many atoms in this piece of Mg?

0.200 g

=

1 mole

24.3 g0.00823 mole

0.00823 mole

=

6.02 x 1023 atom

1 mole

4.95 x 1021 atom

47

MOLECULAR WEIGHT MOLECULAR WEIGHT AND MOLAR MASSAND MOLAR MASS

Molecular weight Molecular weight is the sum

of the atomic weights of all atoms

in the molecule.

Molar massMolar mass = molecular weight

in grams

48

What is the molar mass of What is the molar mass of ethanol, Cethanol, C22HH66O?O?

1 mol contains

2 mol C (12.0 g C/1 mol) = 24.0 g C

6 mol H (1.0 g H/1 mol) = 6.0 g H

1 mol O (16.0 g O/1 mol) = 16.0 g O

TOTAL = molar mass = 46.0 g/mol

49

• Formula = C8H9NO2

• Molar mass = 151.0 g/mol

TylenolTylenol

50

How many moles of alcohol are How many moles of alcohol are there in a “standard” can of beer if there in a “standard” can of beer if there are 21.3 g of Cthere are 21.3 g of C22HH66O?O?

21.3 g=

1 mole

46.0 g0.463 mole0.463 mole

51

How many How many molecules molecules of alcohol of alcohol are there in a “standard” can of are there in a “standard” can of beer if there are 21.3 g of Cbeer if there are 21.3 g of C22HH66O?O?

0.463 mole

=

6.02 x 1023 molecule

1 mole

2.79 x 102.79 x 102323 molecule molecule

52

How many How many atoms of C atoms of C are there are there in a “standard” can of beer if in a “standard” can of beer if there are 21.3 g of Cthere are 21.3 g of C22HH66O?O?


=

2 atom C

1 molecule

5.58 x 105.58 x 102323 atom C atom C

Sample problems

53

Empirical and Molecular Empirical and Molecular FormulasFormulas

A pure compound always consists of the same elements combined in the same proportions by weight.

Therefore, we can express molecular composition as PERCENT BY WEIGHT

Ethanol, C2H6O

52.2% C, 13% H,

34.8% O

54

Percent CompositionPercent CompositionConsider some of the family of

nitrogen-oxygen compounds:

NO2, nitrogen dioxide and closely related, NO, nitrogen monoxide (or nitric oxide)

Structure of NO2 Chemistry of NO, nitrogen monoxide (nitric oxide)

55

Percent CompositionPercent CompositionConsider NO2, Molar mass = ?

What is the weight percent of N and of O?

Wt. % O = 2 (16 .0 g O per mole )

46 .0 g x 100% = 69 .6%

Wt. % N = 14.0 g N

46.0 g NO 2 • 100% = 30.4 %

56

Percent CompositionPercent CompositionWhat are the weight percentages of N What are the weight percentages of N

and O in NO?and O in NO?

Wt. % O = 16.0 g O 30.0 g NO

100% = 53.3%•

57

Percent CompositionPercent CompositionSamples ProblemsSamples Problems

1. Calculate the percent composition of H1. Calculate the percent composition of H22O.O.

Wt. % O = 16.0 g O 18.0 g H2O

• 100% = 88.9%

58


2. Calculate the percent O in NaOH.2. Calculate the percent O in NaOH.

59


3. Calculate the percent O and the 3. Calculate the percent O and the percent water in CuSOpercent water in CuSO44

..5H5H22O. O.

Wt. % O = 144.0 g O

249.6 g CuSO4 • 5H2O • 100% = 57.69 %

60

Determining Determining FormulasFormulas

In chemical analysis we determine the In chemical analysis we determine the

% by weight of each element in a given % by weight of each element in a given

amount of pure compound and derive amount of pure compound and derive

thethe EMPIRICALEMPIRICAL or or SIMPLESTSIMPLEST formula.formula.

61A compound of B and H is A compound of B and H is 81.10% B. What is its empirical 81.10% B. What is its empirical formula?formula?

81.10 g 1 mole

10.8 g

18.90 g 1 mole

1.0 g

BB H H

1.00 mole B 2.5 mole H

7.51mole B 19 mole H

7.51 mole B 7.51 mole B

2.00 mole B 5.0 mole HB2H5

62

A compound of B and H is 81.10% B. A compound of B and H is 81.10% B. Its empirical formula is BIts empirical formula is B22HH55. What is . What is

its its molecular formulamolecular formula??

Is the molecular formula B2H5, B4H10, B6H15, B8H20, etc.?

B2H6 is one example of this class of compounds.

BB22HH66

63A compound of B and H is 81.10% B. A compound of B and H is 81.10% B. Its empirical formula is BIts empirical formula is B22HH55. What is . What is its molecular formula?its molecular formula?

We need to do an EXPERIMENTEXPERIMENT to find the MOLAR MASS.

Here experiment gives 53.3 g/mol.

Compare with the mass of B2H5 , 26.66 g/unit

Find the ratio of these masses.

mol 1

HB of units 2 =

HB ofg/unit 26.66

g/mol 3.53 52

52

Molecular formula =Molecular formula = B B44HH1010

64

Determine the formula of a Determine the formula of a compound of Sn and I using compound of Sn and I using the following datathe following data..

• Reaction of Sn and I2 is done using excess Sn.

• Mass of Sn in the beginning = 1.056 g

• Mass of iodine (I2) used = 1.947 g

• Mass of Sn remaining = 0.601 g

65

Find the mass of Sn that combined with 1.947 g I2.

Mass of Sn initially = 1.056 g

Mass of Sn recovered = 0.601 g

Mass of Sn used = 0.455 g

Tin and Iodine Tin and Iodine CompoundCompound

66

0.455 g 1 mole

118.7 g

1.947 g 1 mole

126.9 g

SnSn I I

1.00 mole Sn 4.01 mole I

0.0383 mole Sn 0.1534 mole I

0.0383 mole Sn 0.0383 mole Sn

SnISnI44

Tin and Iodine Tin and Iodine CompoundCompound

67

More ProblemsMore Problems2. Calculate the formula for the iron sulfide

that forms when 53.73g Fe react with 46.27 g of sulfur.

53.73 g 1 mole

55.8 g

46.27 g 1 mole

32.1 g

FeFe S S

1.00 1.50

0.963 1.44

0.963 0.963

FeFe22SS33

2.00 3.00

68

More ProblemsMore ProblemsCalculate the empirical formula a compound

containing 90.7% Pb and 9.33% O.

90.7 g 1 mole

207.2 g 9.33 g 1 mole

16.0 g

PbPb O O

1.00 1.33

0.438 0.583

0.438 0.438

PbPb33OO44

3.00 3.99

69

More ProblemsMore ProblemsCalculate the empirical formula for a

compound containing 36.5% Na, 25.4% S and 38.1% O.

36.5 g 1 mole

23.0 g

25.4 g 1 mole

32.1 g

NaNa S O S O

2.01 1.00 3.01

NaNa22SOSO33

38.1 g 1 mole

16.0 g

1.59 0.791 2.38

0.791 0.791 0.791

70

More ProblemsCalculate the empirical and molecular

formulas for nicotine, 74.0% C, 8.7% H and 17.3% N, with a molar mass of 160 g/mole.

74.0 g 1 mole

12.0 g

8.7 g 1 mole

1.0 g

C H N

4.98 7.0 1.00

17.3 g 1 mole

14.0 g

6.17 8.7 1.24

1.24 1.24 1.24

Empirical formula C5H7N

71

More ProblemsMore Problems7. Calculate the empirical and molecular

formulas for nicotine, 74.0% C, 8.7% H and 17.3% N, with a molar mass of 160 g/mole.

Empirical formula C5H7N

Molecular formula C10H14N2

160= 2

81

72

Practice ProblemsPractice Problems

Names/FormulasNames/Formulas

FeO

Pb(C2H3O2)2

magnesium bromide

sodium chromate

calcium phosphate

ammonium carbonate

73


(NH4)2S

As2O3

SO2

silicon disulfide

As2S5

dinitrogen monoxide

74


As2S3

dinitrogen pentoxide

silicon tetrabromide

diphosphorus pentoxide

HBrO3

H3PO4(aq)

H2CO3

75

Practice ProblemsPractice ProblemsCalculations

1. 26 g H2 is how many moles H2?

2. 4.25 x 1021 molecules NH3 is how many grams NH3?

3. 1.5 x 102 formula units KClO3 is how many moles KClO3

4. 0.0042 mole Fe2O3 is how many formula units Fe2O3?

5. 2.15 moles MgSO4.7H2O is how many g

MgSO4.7H2O?

76

Practice ProblemsPractice Problems6. 25 molecules HBr is how many mole

HBr?7. .00002 g Sn is how many atoms Sn?

8. 7.25 mole H2S is how many g H2S?

9. 5.2 g Sr(OH)2is how many formula units Sr(OH)2?

10. How many moles of CCl4 will contain 2.4 g of chlorine?

77


11. 19 g of HNO3 contains how many

a) molecules of HNO3? b) grams of O?

12. Calculate the percent composition of NaCl.

13. Calculate the empirical and molecular formulas for a compound containing 43.7g P and 56.3g O, with a molar mass of 140 g/mole.

78

Practice Problems AnswersPractice Problems AnswersIron(II) oxide, ferrous oxide

lead(II) acetate, plumbous acetate

MgBr2 Na2CrO4 Ca3(PO4)2

(NH4)2CO3 ammonium sulfide

diarsenic trioxide sulfur dioxide

SiS2 As2S5 N2O

diarsenic trisulfide N2O5 SiBr4

P2O5 bromic acid phosphoric acid

carbonic acid

79

Practice Problems AnswersPractice Problems Answers1. 13 mole 2. 0.120 g

3. 2.5 x 10-22 mole 4. 2.5 x 1021 atom

5. 530. g 6. 4.2 x 10-23 mole

7. 1 x 1017 atom 8. 247 g

9. 2.6 x 1022 formula units

10. 0.017 mole

11. a) 1.8 x 1023 molecule

b) 14 g

12. 39.3%, 60.7% 13. C5H7N

14. P2O5

80

Sample QuestionsSample Questions• Predict the charges for the ions formed

from:Se -2 Ga +3 Al3+

P -3 Sr +2 SO42-

• Give the formula for each ion in Al2(SO4)3

• Give the formula for the ionic compound

that forms between Na and S Na2S

Ga and O Ga2O3

Ba and N Ba3N2

81

Sample ProblemsSample Problems

1. 2.5 mole S = ? atom S 2.5 mole

=

6.02 x 1023 atom

1 mole

1.5 x 1024 atom S

82

Sample ProblemsSample Problems2. 2.1 mole Zn = ? g Zn

2.1 mole=

65.4 g

1 mole 140 g Zn140 g Zn

83


3. 1.42 g Mg = ? atom Mg3. 1.42 g Mg = ? atom Mg

1.42 g

=

1 mole

24.3 g

3.55 x 103.55 x 102222 atom atom

6.02 x 1023 atom

1 mole

84


4. 125.2 g O4. 125.2 g O22 = ? mole O = ? mole O22

125.2 g=

1 mole

32.0 g3.91 mole O3.91 mole O22

85


1. 1.5 mole H1. 1.5 mole H22O = ? g HO = ? g H22OO

1.5 mole=

18.0 g

1 mole 27 g H27 g H2200

86


2. 1.502. 1.50 mole CCl mole CCl44 = ? molecules CCl = ? molecules CCl44

1.5 mole

=


1 mole

9.03 x 109.03 x 102323 molecule molecule

87


3. 1.25 mole CaCl3. 1.25 mole CaCl22 = ? formula units CaCl = ? formula units CaCl22

1.25 mole

=

6.02 x 1023 formula unit

1 mole

7.52 x 107.52 x 102323 formula unit formula unit

88


4. 2.5 g K = ? g KOH4. 2.5 g K = ? g KOH

2.5 g K

=

1 mole K

39.1 g K

3.6 g KOH3.6 g KOH

1 mole KOH

1 mole K

56.1 g KOH

1 mole KOH

89


5.5. 34.5 g CaCO 34.5 g CaCO33 = ? g O = ? g O

34.5gCaCO34.5gCaCO33

==

1 moleCaCO1 moleCaCO33

100.1gCaCO100.1gCaCO33

16.5 g O16.5 g O

3 moleO3 moleO

1 moleCaCO1 moleCaCO33

16.0 gO 16.0 gO

1 moleO1 moleO

1 molecules and compounds read chapter 3. study all examples and complete all exercises. complete...

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