Chapter 5 Molecules and Compounds · Chapter 5 Molecules and Compounds . Tro's "Introductory Chemistry", Chapter 5 2 ... Chapter 5 23 Metal Cations 23 TYPE 2

Chapter 5

Molecules and

Compounds

Tro's "Introductory Chemistry",

Chapter 5

2

Molecules and Compounds • When elements combine to form

compounds their properties change

• Salt

Sodium—shiny, reactive, poisonous.

Chlorine—pale yellow gas, reactive, poisonous.

Sodium chloride—table salt.

• Sugar

Carbon—pencil or diamonds.

Hydrogen—flammable gas.

Oxygen—a gas in air.

Combine to form white crystalline sugar.


Chapter 5

3

Compounds Display Constant

Composition • All pure substances have constant composition.

All samples of a pure substance contain the same

elements in the same percentages (ratios).

Mixtures have variable composition.


Chapter 5

4

Example: Constant Composition

If we decompose water, we find 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.

0.8g 2.0

g 0.16

hydrogen of mass

oxygen of mass Ratio Mass


Chapter 5

5

How to Represent Compounds • A compound is substance that is composed of atoms

of two or more elements.

• Compounds can be represented

Writing the symbol of each element present in the compound.

describing the number of each atom in the simplest unit of the compound.

• The number of atoms of each element is written to the right of the element as a subscript.

If there is only one atom, the 1 subscript is not written.

• Polyatomic groups are placed in parentheses.

If more than one.


Chapter 5

6

Water = H2O \ two atoms of

hydrogen and 1 atom of oxygen

Table sugar = C12H22O11 \12 atoms

of C, 22 atoms of H and 11 atoms O

How to Represent Compounds


Chapter 5

7

Order of Elements in a Formula • Metals are written first.

NaCl

• Nonmetals are written in order from

Table 5.1.

CO2

There are occasional exceptions for

historical or informational reasons.

H2O, but NaOH .

Table 5.1

Order of Listing Nonmetals in Chemical Formulas

C P N H S I Br Cl O F


Chapter 5

8

Example—Write Formulas for Each of the

Following Compounds.

• Hematite—Composed of four oxide ions for

every three iron ions.

• Acetone—Each molecule contains six

hydrogen atoms, three carbon atoms, and

one oxygen atom.

Fe3O4

C3H6O


Chapter 5

9

Molecules with

Polyatomic Ions

Mg(NO3)2

Compound called

magnesium nitrate.

Symbol of the polyatomic

ion called nitrate.

Symbol of the polyatomic

ion called sulfate.

CaSO4

Compound called

calcium sulfate.

Implied “1” subscript

on magnesium.


on calcium.

Parentheses to group two NO3s. No parentheses for one SO4.

10

Molecules with

Polyatomic Ions, Continued

Mg(NO3)2

Compound called

magnesium nitrate.

CaSO4

Compound called

calcium sulfate.

Subscript indicating

two NO3 groups. No subscript indicating

one SO4 group.


on nitrogen, total 2 N.


on sulfur, total 1 S.

Stated “3” subscript

on oxygen, total 6 O.

Stated “4” subscript

on oxygen, total 4 O.


Chapter 5

11

Example—Determine the Total Number of Atoms

or Ions in One Formula Unit of Each of the

Following.

• Mg(C2H3O2)2

• Practice

• (Hg2)3(PO4)2

1 Mg + 4 C + 6 H + 4 O = 15


Chapter 5

12

Classifying Materials

• Atomic elements = Elements whose

particles are single atoms.

• Molecular elements = Elements whose

particles are multi-atom molecules.

• Molecular compounds = Compounds

whose particles are molecules made of only

nonmetals.

• Ionic compounds = Compounds whose

particles are cations and anions.

13

Molecular Elements

• Certain elements occur as diatomic molecules.

i.e., two atoms of the same element bonded together

H2

Cl2

Br2

I2

7

7A

N2 O2 F2


Chapter 5

14

Molecular Compounds

• Two or more

nonmetals.

• Smallest unit is a

molecule.


Chapter 5

15

Ionic Compounds

• Metals + nonmetals.

• No individual

molecule units, instead

have a 3-dimensional

array of cations and

anions made of

formula units.

16

Molecular View of

Elements and Compounds


Chapter 5

17

Classify Each of the Following as Either an

Atomic Element, Molecular Element,

Molecular Compound, or Ionic Compound,

Continued. • Aluminum, Al

• Aluminum chloride, AlCl3

• Chlorine, Cl2

• Acetone, C3H6O

• Carbon monoxide, CO

• Cobalt, Co

= Atomic element.

= Ionic compound.

= Molecular element.

= Molecular compound.

= Molecular compound.

= Atomic element


Chapter 5

18

Ionic Compounds

• Ionic compounds are made of ions.

• Ionic compounds always contain cations and anions.

Cations = + charged ions; anions = − charged ions.

• The sum of the + charges of the cations must equal the sum of the − charges of the anions.

• If Na+ is combined with S2-, you will need 2 Na+ ions for every S2- ion to balance the charges, therefore the formula must be Na2S.


Chapter 5

19

Writing Formulas for

Ionic Compounds

NAME-TO-FORMULA

1. Write the symbol for the metal cation and its charge.

2. Write the symbol for the nonmetal anion and its charge.

3. Charge (without sign) becomes subscript for the other

ion.

4. Reduce subscripts to smallest whole-number ratio.

5. Check that the sum of the charges of the cation cancels

the sum of the anions.


Chapter 5

20

Write the Formula of a Compound Made from

Aluminum Ions and Oxide Ions.

1. Write the symbol for the metal

cation and its charge.

2. Write the symbol for the

nonmetal anion and its charge.

3. Charge (without sign) becomes

subscript for the other ion.

4. Reduce subscripts to smallest

whole-number ratio.

5. Check that the total charge of

the cations cancels the total

charge of the anions.

Al+3 column 3A

O2- column 6A

Al+3 O2-

Al2O3

Al = (2)∙(+3) = +6

O = (3)∙(-2) = -6


Chapter 5

21

Practice—What Are the Formulas for

Compounds Made from the Following

Ions?

• Potassium ion with a nitride ion.

• Calcium ion with a bromide ion.

• Aluminum ion with a sulfide ion.


Chapter 5

22

Metal Cations

22

TYPE 1

• Main group metals

have invariant charge i.e., metals whose ions can have only one possible charge

Groups 1A & 2A,

Al3+, Ag1+, Zn2+, Sc3+

cation name = metal name


Chapter 5

23

Metal Cations

23

TYPE 2

• Transition metals

metals with variable

charges i.e., metals

whose ions can have

more than one possible

charge

determine charge of

cation by charge on

anion

name = metal name

with Roman numeral

charge in parentheses


Chapter 5

24

24

Naming Monatomic Nonmetal Anion

• 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


Chapter 5

25

25

Naming Ionic Compounds

FORMULA-TO-NAME

• Recall: ionic compounds are made of cations and anions

• Name the cation first, followed by the anion

if cation is:

main group metal = metal name

transition metal = metal name(charge)

polyatomic ion = name of polyatomic ion

if anion is:

nonmetal = stem of nonmetal name + -ide

polyatomic ion = name of polyatomic ion


Chapter 5

26

26

1) Naming binary Ionic Compounds for

Metals with Invariant Charge

2) Naming Binary Ionic Compounds for

Metals with Variable Charge

Su

mm

ary

Su

mm

ary

S

um

mary


Chapter 5

27

Example : What is the name of the

compound CsF

27

1. Identify cation and anion.

Cs = Cs+ because it is in Group 1A

F = F– because it is in Group 7A

2. Name the cation.

Cs+ = cesium

3. Name the anion.

F– = fluoride

4. Write the cation name first, then the anion name.

cesium fluoride


Chapter 5

28

Practice: Name the following compounds

28

1. KCl

2. MgBr2


Chapter 5

29

29

Determining the Charge on a Cation with

Variable Charge e.g., Au2S3 1. Determine the charge on the anion

Au2S3—The anion is S. Since it is in Group 6A, its charge is 2−

2. Determine the total negative charge

Since there are 3 S in the formula, the total negative charge is −6

3. Determine the total positive charge

Since the total negative charge is −6, the total positive charge is +6

4. Divide by the number of cations

Since there are 2 Au in the formula and the total positive charge is +6, each Au has a 3+ charge


Chapter 5

30

Practice : Find the charge on the cation.

30

CrO3

Fe3N2


Chapter 5

31

31

Example: Naming Binary Ionic

with Variable Charge Metal CuF2

1. Identify cation and anion

F = F− because it is Group 7

Cu = Cu2+ to balance the two (−) charges from 2 F−

2. Name the cation

Cu2+ = copper(II)

3. Name the anion.

F− = fluoride

4. Write the cation name first, then the anion name.

copper(II) fluoride


Chapter 5

32

32

Practice: Name the following compounds.

1. TiCl4

2. Fe2S3


Chapter 5

33

33

Example: Writing Formula for Binary Ionic

Compounds Containing Variable Charge Metal

manganese(IV) sulfide

1. Write the symbol for the cation

and its charge

2. Write the symbol for the anion

and its charge

3. Switch charge (without sign)

each ion to become subscript

for the other ion


whole number ratio



charge of the anions

Mn4+

S2–

Mn4+ S2− Mn2S4

Mn = (1) × (4+) = +4

S = (2) × (2–) = −4

MnS2


Chapter 5

34

34

Practice: What are the formulas for

compounds made from the following ions?

1) copper(II) nitride

2) iron(III) bromide


Chapter 5

35

35

Compounds Containing

Polyatomic Ions

• Polyatomic ions are single ions that contain

more than one atom

• Name and charge of polyatomic ion do not

change

• As usual, name any ionic compound by naming

cation first and then anion

Some Common Polyatomic Ions

Name Formula

acetate C2H3O2–

carbonate CO32–

hydrogen carbonate HCO3–

hydroxide OH–

nitrate NO3–

nitrite NO2–

chromate CrO42–

dichromate Cr2O72–

cyanide CN–

permanganate MnO4–

ammonium NH4+

Name Formula

hypochlorite ClO–

chlorite ClO2–

chlorate ClO3–

perchlorate ClO4–

sulfate SO42–

sulfite SO32–

hydrogen sulfate HSO4–

hydrogen sulfite HSO3–

phosphate PO43–

phosphite PO33–


Chapter 5

37

37

Patterns for Polyatomic Ions

1. The ‘ate ’ and the ‘ite’ ions. Ions with same

charge but one less oxygen atom.

NO3– Nitrate

NO2– Nitrite

2. hydrogen- prefix before name and add 1 to the

charge

CO32– = carbonate \ HCO3

– = hydrogen carbonate


Chapter 5

38

38

Periodic Pattern of Polyatomic Ions

-ate groups

3A 4A 5A 6A 7A

BO33−

borate

CO32−

carbonate

NO3−

nitrate

SiO32−

silicate

PO43−

phosphate

SO42−

sulfate

ClO3−

chlorate

AsO43−

arsenate

SeO42−

selenate

BrO3−

bromate

TeO42−

tellurate

IO3−

iodate


Chapter 5

39

39

Patterns for Polyatomic Ions

• -ate ion

chlorate = ClO3–

• -ate ion + 1 O same charge, per- prefix

perchlorate = ClO4–

• -ate ion – 1 O same charge, -ite suffix

chlorite = ClO2–

• -ate ion – 2 O same charge, hypo- prefix, -ite

suffix

hypochlorite = ClO–


Chapter 5

40

40

Example: Writing Formula for Ionic

Compounds Containing Polyatomic Ion

Iron(III) phosphate


and its charge


and its charge

3. Switch the charge (without

sign) of each ion to become

subscript for the other ion


whole number ratio.



charge of the anions

Fe3+

PO43−

Fe3+ PO43− Fe3(PO4)3

Fe = (1) × (3+) = +3

PO4 = (1) × (3−) = −3

FePO4


Chapter 5

41

41

Practice: Write the chemical formula of the

following compounds?

aluminum sulfate

chromium(II) hydrogencarbonate


Chapter 5

42

Example—Naming Ionic with Polyatomic Ion,

Na2SO4 1. Identify cation

Na is the cation because metals form positive charge.

• Is the metal Type I or Type II?

Na is in Group 1A, \ Type I.

Hence, charge on Na is +1

• Identify anion

Anion is SO4

Polyatomic, because it contains TWO OR MORE different types of elements


Chapter 5

43

4. Name the cation.

Na+ = sodium (Type I).

5. Name the anion.

SO42- = sulfate.

6. Write the name of the cation followed by the name of the anion.

sodium sulfate.


Na2SO4 , Continued


Chapter 5

44


Fe(NO3)3 1. Identify cation

Fe is the cation because metals form positive charge.

• Is the metal Type I or Type II? Fe is a transition metal, \ Type II.

Caution!!: Transition metals have variable charge, so we need to find out what the charge on the anion

• Identify anion Anion is NO3

polyatomic because it contains TWO OR MORE different types of elements


Chapter 5

45

4. Name the anion. NO3

- = nitrate

5. Name the cation. Fe3+ = iron(III) (Type II).

Based on the charge of the nitrate group

6. Write the name of the cation followed by the name of the anion.

iron(III) nitrate.


Fe(NO3)3 , Continued


Chapter 5

46

Practice─Name the Following

1. NH4Cl

2. Ca(C2H3O2)2

3. Cu(NO3)2


Chapter 5

47

47

Writing Names of Binary Molecular

Compounds of Two Nonmetals 1. Write the name of the first element in the formula Use the full name of the element,

2. Write the name of the second element in the formula with an -ide suffix 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.


Chapter 5

48

Subscript—Prefixes

48

• 1 = mono-

not used on first nonmetal

• 2 = di-

• 3 = tri-

• 4 = tetra-

• 5 = penta-

• 6 = hexa-

• 7 = hepta-

• 8 = octa-

• 9 = nona-

• 10 = deca-

• Drop last “a” or “o” if name begins with a vowel.


Chapter 5

49

49

Example: Naming Binary Molecular.

e.g., BF3

1. Name the first element.

boron

2. Name the second element with an -ide.

fluorine fluoride

3. Add a prefix to each name to indicate the subscript.

monoboron trifluoride

Drop the prefix mono from the first element.

boron trifluoride


Chapter 5

50

50

Practice: Name the following.

N2O4

PCl5

I2F7

CO


Chapter 5

51

51

Example: Binary Molecular

dinitrogen pentoxide

• Identify the symbols of the elements.

nitrogen = N

oxide = oxygen = O

• Write the formula using prefix number for

subscript.

di = 2, penta = 5

N2O5


Chapter 5

52

52

Practice: Write formulas for the following.

dinitrogen tetroxide

sulfur hexafluoride

diarsenic trisulfide


Chapter 5

53

53

Acids • Acids are molecular compounds that form H+

when dissolved in water.

To indicate the compound is dissolved in water, (aq) is written after the formula.

not named as acid if not dissolved in water

• sour taste (please never taste it!!)

• dissolve many metals

like Zn, Fe, Mg; but not Au, Ag, Pt

• formula generally starts with H

e.g., HCl, H2SO4


Chapter 5

54

54

Acids

• Dissolve in aqueous solution to form H+ cation and anion

• Binary acids have H+ cation and nonmetal anion

• Oxyacids have H+ cation and polyatomic anion


Chapter 5

55

55

1. Identify the anion

2. Name the anion with an -ic suffix

3. Add a hydro- prefix to the anion name

4. Add the word acid to the end

Naming Binary Acids


Chapter 5

56

56

Example: Naming Binary

Acids. e.g., HCl(aq) 1. Identify the anion

Cl = Cl−, chloride because Group 7A

2. Name the anion with an -ic suffix

Cl− = chloride chloric

3. Add a hydro- prefix to the anion name

hydrochloric

4. Add the word acid to the end

hydrochloric acid


Chapter 5

57

57

Naming Oxyacids

1) Identify the polyatomic ion (anion)

The poly atomic ion in this case will always

contain oxygen

2) If the polyatomic ion name ends in -ate, then

change ending to -ic suffix

3) If the polyatomic ion name ends in -ite, then

change ending to -ous suffix

4) Write word acid at the end of all names.


Chapter 5

58

58

Example:

Naming Oxyacids. HNO3(aq)

1. Identify the polyatomic ion

NO3 = NO3− = nitrate

2. If the anion has -ate suffix, change it to -ic. If the anion has -ite suffix, change it to -ous.

NO3− = nitrate nitric

3. Write the name of the anion followed by the word acid.

nitric acid


Chapter 5

59

59

Example:

Naming Oxyacids. HNO2(aq)

1. Identify the polyatomic ion

NO2 = NO2− = nitrite

2. If the anion has -ate suffix, change it to -ic. If the anion has -ite suffix, change it to -ous.

NO2− = nitrite nitrous


nitrous acid


Chapter 5

60

60

Example: Naming Oxyacids

H2SO4(aq)

1. Identify the anion

SO4 = SO42− = sulfate

2. If the anion has -ate suffix, change it to -ic. If the anion has -ite suffix, change it to -ous

SO42− = sulfate


sulfuric acid

sulfuric


Chapter 5

61

61

Practice: Name the following

HBr (aq)

HClO3(aq)

H3PO4(aq)


Chapter 5

62

62

Writing Formulas for Acids

1) when name ends in acid, formula starts with H

2) Hydro prefix means it is a binary acid, no prefix means it is an oxyacid

3) Locate the cation and the anion

NB: In acids the cation is always H+

4) for oxyacid, if ending is -ic, polyatomic ion ends in -ate; if ending is -ous, polyatomic ion ends in –ite

5) write formulas as if ionic, even though it is molecular


Chapter 5

63

63

Example: Binary Acids

hydrobromic acid


and its charge.


and its charge.

3. Switch charges (without sign) for

each ion to subscript for the other

ion.

4. Add (aq) to indicate dissolved in

water.

H+

Br−

H+ Br− HBr

HBr(aq)

In all acids, the

cation is H+.

Hydro means

binary.


Chapter 5

64

64

Example: Oxyacids

carbonic acid


and its charge


and its charge

3. Switch charge (without sign) for

each ion to become subscript for

the other ion

4. Add (aq) to indicate dissolved in

water

H+

CO32−

H+ CO32− H2CO3

H2CO3(aq)

In all acids, the

cation is H+.

No hydro means

polyatomic ion.

-ic means -ate ion.


Chapter 5

65

65

Example: Oxyacids

sulfurous acid


and its charge.


and its charge.

3. Switch charge (without sign) of

each ion to become subscript

for the other ion

4. Add (aq) to indicate dissolved

in water.

H+

SO32−

H+ SO32− H2SO3

H2SO3(aq)

In all acids, the

cation is H+.

No hydro means

polyatomic ion.

-ous means -ite ion.


Chapter 5

66

66

Practice: What are the formulas for the

following acids?

chlorous acid

phosphoric acid

hydrobromic acid

Compounds With Trivial Names

Name Formula

Water H2O

Methane CH4

Ammonia NH3


Chapter 5

67

67


Chapter 5

68

Formula-to-Name Flowchart


Chapter 5

69

Formula Mass

• The 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 H2O

= 2(1.01 amu H) + 16.00 amu O = 18.02 amu.


Chapter 5

70

Example—Calculate the Formula Mass of

Al2(SO4)3

amu 17.342)(SOAl

amu 16.00 12O

amu 32.07 3S

amu 26.98 2Al

342


Chapter 5

71

Practice—Calculate the Formula Mass of

Fe2(CO3)3

Answer = 291.73 amu


Chapter 5

72

Recommended Study Problems Chapter 5

NB: Study problems are used to check the student’s understanding

of the lecture material. Students are EXPECTED TO BE ABLE

TO SOLVE ALL THE SUGGESTED STUDY PROBLEMS.

If you encounter any problems, please talk to your professor or seek

help at the HACC-Gettysburg learning center.

Questions from text book Chapter 5, p 151

23, 25, 29, 31, 33, 35, 39, 41, 49, 51, 55, 57, 61, 63, 67, 69, 71-78

ANSWERS

-The answers to the odd-numbered study problems are found at

the back of your textbook

Chapter 5 Molecules and Compounds · Chapter 5 Molecules and Compounds . Tro's "Introductory Chemistry", Chapter 5 2 ... Chapter 5 23 Metal Cations 23 TYPE 2

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