ch 8 - compounds & molecules 8.1 ionic compounds – fr 2-28 8.2 molecular compounds - fr 29-52...

Ch 8 - Compounds & Molecules

8.1 Ionic Compounds – Fr 2-288.2 Molecular Compounds - Fr 29-528.3 Intermolecular Forces – Fr 53- 82

8.4 Formula Masses – Fr 83-110

In early chapters we discussed physical and chemical properties

In later chapters we discussed atom structures and chemical bonding

Physical and chemical

properties

Atom structures and

chemical bonding

Each chloride ion is attracted to all nearby

sodium ions

Each sodium ion is attracted to all nearby

chloride ions

Structure of NaCl

We have seen that in an ionic salt each atom interacts with all its neighbors.

In any ionic crystal, the ratio of positive ions to negative ions must allow for all of the positive charge to cancel out all of the negative charge.

Lead(II) sulfide(PbS)

Aluminum oxide(Al2O3)

Copper(II) sulfate(CuSO4)

Pb2+ and S2–

(+2) and (–2)2Al3+ and 3O2–

(+6) and (–6)Cu2+ and SO4

2–

(+2) and (–2)

The ionic structure leads to the following physical properties:

Ionic substances are solid at room temperature

Ionic substances have very high melting points

Properties

To be in a liquid state, there must be enough energy for each atom to break free from the attractive forces from its neighbors.

The interconnected network of bonds holds the entire crystal together




Ionic substances are hard

Properties

Ionic substances are brittle, which means they break




Ionic substances are hard but brittle

Properties

When melted or dissolved, ions are free to move around, making it possible for an ionic solution to conduct electricity

Ions dissolved in water move in random directions by colliding

with water molecules

Overall ion movement toward the electrodes creates an

electrical current

Properties

Polyatomic ions

An ion does not have to be a single atom. An ion can be a small molecule with a charge.

a polyatomic ion

a monatomic ion

Polyatomic ions

Calcium carbonate, CaCO3

The calcium ion contributes a +2 charge (Ca2+)

The CO3 molecule needs two extra electrons.

Polyatomic ions

The two oxygens now have a –1 charge,

giving the whole molecule a –2 charge

The carbonate ion switches among these three versions.

Ammonium sulfate (NH4)2SO4 is made from two polyatomic ions

Now we will learn how to:

- Write formulas for ionic compounds

- Write names for ionic compounds

- Name ions with transition metals

Balancing positive and negative charge in ionic formula writing

Writing formulas

Write the correct formulas for the compounds that will form using the following ion pairs: Mg2+ and Cl–, Na+ and S2–, Al3+ and O2–.

Writing formulas

Writing names

With monatomic ions:

Writing names

Names for polyatomic ions

Writing names

With polyatomic ions:With monatomic ions:

Naming transition metal ions

Most transition metals can have different charges

Check whether a Roman numeral is necessary for elements in the highlighted parts of the

periodic table

A Roman numeral indicates the charge on a positive ion


Consider PbCl2

Check the common ions table

Use the negative ion to determine the charge on lead

With only one Pb ion, and a total charge of +2 needed,

the Pb ion must be lead(II)


Check the common ions table

Zn only forms a +2 ion

No Roman numeral is needed

Consider ZnSO4

Write the names for each of the following formulas: CaCl2, Zn(NO3)2, Fe3(PO4)2.

Asked: Names for the formulas aboveGiven: Three formulas and a common ion tableRelationships: The name of each formula is

constructed form the name of the ions. If the negative ion is a single atom, modify the name of the element to end in “-ide.” If the positive ion might form multiple charges, make sure to use a Roman numeral in the name.

Write the names for each of the following formulas: CaCl2, Zn(NO3)2, Fe3(PO4)2.

Asked: Names for the formulas aboveGiven: Three formulas and a common ion tableRelationships: The name of each formula is

constructed form the name of the ions. If the negative ion is a single atom, modify the name of the element to end in “-ide.” If the positive ion might form multiple charges, make sure to use a Roman numeral in the name.

Solve: CaCl2 is calcium chloride.Zn(NO3)2 is zinc nitrate.Fe3(PO4)2 is iron(II) phosphate.

Naming simple molecular compounds

P2S3

Consider the following molecular compound:

two phosphorous atomswith three sulfur atoms

diphosphorous trisulfide


H2O


two hydrogen atomswith one oxygen atom

dihydrogen monoxide

(another name for water)


CO


one carbon atomwith one oxygen atom

carbon monoxide

Drop “mono” for the first element


Write the name for each of the following formulas:

N2O4,

S2F10,

SO3.


Write the name for each of the following formulas: N2O4, S2F10, and SO3.

Solve: N2O4 is dinitrogen tetraoxide.

S2F10 is disulfur decafluoride.

SO3 is sulfur trioxide.

Properties of molecular compounds vary widely

HardnessSome are hard and brittle; some are flexible,

soft or mushyState of matter

They can be solid, liquid or gas at room temperatureBoiling points

Their boiling points can vary from –253oC to over 1,000oCAbility to conduct electricity

Most do not conduct electricity well

Water

Water is a covalent compoundAbout eight million billion billion (1024) water molecules make up

this cup of water

Properties of molecular substances depend

on:

- the structure of the individual molecule

- the attractions between molecules

Small

Caffeine, found in tea, coffee,

and soda

Medium

Wax, one of the main hydrocarbons

in beeswax

Molecules can be classified into different categories

Large: polymer Large: network

Protein,molecule on the right shows a thick line

tracing the linear chain with red and blue marking either end

Graphene,layers of which make

graphite

Molecules can be classified into different categories

Small molecules

Acetaminophen(Tylenol)

is a liquid at room temperature

Most small molecules (no more than a dozen atoms) are liquids or gases at room temperature

Some of the most important molecules related to our ecosystem are small molecules

Water

If ice did not float, ponds would freeze from the bottom up, killing everything inside.

Most small molecules (no more than a dozen atoms) are liquids or gases at room temperature

Some of the most important molecules related to our ecosystem are small molecules

Small molecules

Ethene(or ethylene)

Nonpolar (gas at room temperature)Boiling point = –103.7oC

Ethanol

Polar (liquid at room temperature)Boiling point = 78.4oC

Medium-sized molecules

Candle wax is a mixture of medium-sized hydrocarbons

Medium-sized molecules (no more than 100 atoms) tend to be liquids or soft solids at room temperature.

They are often long-chain hydrocarbons or lipids

hydrocarbon: a molecule made entirely from carbon and hydrogen atoms.


Linoleic acid, a major component of vegetable oil

Lipids are typically fats or steroids

Fats are nonpolar and insoluble in water


Testosterone(a steroid)

Most steroids have four rings of carbon atoms.

They can act as hormones, drugs, vitamins, or poisons

1

2

3

4

Polymers

Polyvinyl chloride (PVC) is made by bonding

many vinyl chloride monomers together

A single monomer of vinyl chloride

A single polymer chain typically contains hundreds to thousands of atoms

Recycling symbols and polymer codes

Polymers

polymer: a long chain molecule formed by connecting small repeating units with covalent bonds.

monomer: a small molecule that is a building block of larger molecules called polymers.

Polyvinyl chloride

Polymers

Glucosea natural monomer

Cellulose fragment

Starch fragment

Homopolymers are made from only one type of monomer

Networks

network covalent: a type of large structure, usually made from hundreds to billions of atoms, in which each atom is covalently bonded to multiple neighboring atoms, forming a web of connections.

Silicon dioxide (or quartz)is a mineral in sand

Since every atom in quartz is covalently bonded together, the entire grain can be considered a single network.

Networks

Carbon forms many types of network covalent substances

Diamond BuckyballsCarbon nanotubes

Graphite

Chemical formulas

Use the empirical formula to describe the simplest ratio of elements of that substance

a molecule of water

Use the molecular formula to indicate the exact type and number of each atom in a single molecule of that substanceA sample of ionic or network covalent

substance is a single bonded unit of material

Use the molecular formula to indicate the exact type and number of each atom in a single molecule of that substance

Chemical formulas

Benzene

Empirical formula: Molecular formula:

CH C6H6

a molecule of water

Write the molecular formula for each of the following molecules:

Chemical formulas

Write the molecular formula for each of the following molecules:

Chemical formulas

Asked: The molecular formulaRelationships: The formula should reflect the

exact number and type of atoms in an individual molecule of the substance.

Solve: A. C2H2 B. NH3 C. C2H5O

We have seen in Chapter 3 that molecules in solids and liquids are held together by intermolecular forces

What are these forces? Where do they come from? Do all molecules feel them?

A tiny drop of waterIntermolecular attraction

As a liquid, water molecules can move around but intermolecular forces keep them from separating completely to become a gas.

A quick look at water

strong

London dispersion Dipole-dipole Hydrogen bonding

Types of intermolecular attractions

Betweenpolar molecules

Betweennonpolar molecules

Intermolecular attractions are also called van der Waals attractions

Intermolecular attractionsweak

Dipole-dipole attractions

Like water, formaldehyde is a polar molecule

The polar covalent C=O bond makes the entire molecule polar

We say the molecule has a dipole

dipole-dipole attraction: the attractions between the positive part of one polar molecule and the negative part of another polar molecule.


Like water, formaldehyde is a polar molecule


Dipole-dipole attractions cause formaldehyde to condense into a liquid at room temperature


more

less


Molecules that are more polar will attract strongly.

Boiling point


Molecules that are more polar will attract strongly. more

less

Molecules that attract more strongly

will have a boiling point. higher

lower

Boiling point



will have a boiling point.

higher

lower

Molecules that are more polar will attract strongly. more

less


Higher polarity molecules attract more strongly and have a higher boiling point

propane 1-propanol 1,3-propanediol

least polar

most polar

–42oC 97oC 214oCBoiling points

strong







Hydrogen bonding

Electronegativity

There is a moderate difference in electronegativity between H and F, O and N (0.94 to 1.88)

Hydrogen bonding

Water molecules are held together by a network of hydrogen bonding

Hydrogen bonding

Iceberg photo courtesy of NOAA

One special property of water:Ice is less dense than water in the liquid form

There is more space in between water molecules in ice Water in the liquid form

Hydrogen bonding

surface tension: a force acting to pull a liquid surface into the smallest possible area.

Why a drop of water doesn’t “lie flat” on a hard surface:

In reality water molecules are much, much smaller than on the drawing!

H-bonds keep the water molecules together

Hydrogen bonding

Surface tension from hydrogen bonds allows a water strider to “walk” on water

Hydrogen bonding

DNA uses hydrogen bonds to hold the two strands together

Hydrogen bonds

Hydrogen bonding plays a crucial role in DNA and protein structures

Hydrogen bonding

Hydrogen bonding plays a crucial role in DNA and protein structures

The protein structure is stabilized with H bonds

Hydrogen bonding

Paper glue is a mixture of polyvinyl acetate (PVA) and water

In “wet” glue, polymer molecules are lubricated by water

Hydrogen bonding

Paper glue is a mixture of polyvinyl acetate (PVA) and water

In “wet” glue, polymer molecules are lubricated by water

As glue dries, many more H-bonds form between the polymer molecules, so the glue hardens

strong







London dispersion

Isolated hydrogen molecules are nonpolar

A temporary, very small polarity can be induced when nonpolar molecules are close enough

Molecules with a larger surface area

will attract ____strongly. more

less

London dispersion

propane

pentane

A temporary, very small polarity can be induced when nonpolar molecules are close enough


will attract ____strongly.

Boiling point



lower

more

less

London dispersion

Boiling point



lower

London dispersion

(It takes more energy to overcome the intermolecular forces.)

more


will attract ____strongly. less

Molecules with larger surface area attract more strongly and have a higher boiling point

propane butane pentane

least surface area

–42oC 0oC 36oCBoiling points

most surface area

London dispersion

London dispersion

The shape of the molecule also matters!

About the same surface area

Stronger attraction Weaker attractionHigher boiling point Lower boiling point

Intermolecular attractionsweak strong






Molar mass

Atomic mass is the molar mass for that

element

Molar mass

Calculating molar mass

H2SO4

Subscripts apply only to the element or group they follow

For H: 2 x 1.0079 g/mole = 2.02 g/mole

For S: 1 x 32.065 g/mole = 32.07 g/mole

For O: 4 x 15.999 g/mole = 64.00 g/mole

For H2SO4: 98.08 g/mole

Molar mass

Calculating molar mass

(NH4)3PO4

If the subscript follows a parenthesis, then multiply everything inside the parentheses by the subscript

For N: 3 x 14.007 g/mole = 2.02 g/mole

For H: 12 x 1.0079 g/mole = 32.07 g/mole

For P: 1 x 30.974 g/mole = 30.97 g/mole

For O: 4 x 15.999 g/mole = 64.00 g/mole

For (NH4)3PO4: 149.08 g/mole

What is the molar mass of aluminum carbonate, Al2(CO3)3?

Molar mass

What is the molar mass of aluminum carbonate, Al2(CO3)3?

Molar mass

Asked: The molar mass

Given: The name of the formula

Relationships: The name of the formula can be used to determine the ratios of elements in the formula. Then the periodic table can be used to get the molar mass of each of the elements used.

Solve: Aluminum carbonate is ionic, so the formula is Al2(CO3)3.

Percent composition

You can identify a compound using the percent mass of each element.

NaCl

% by atom numberNa: 50% Cl: 50%

% by massNa: 39% Cl: 61%

1 mole of Cl is heavier than 1 mole of Na

Calculate % composition using a chemical formula

Calculate % composition with a measured sample

Two types of problems

Find the % composition of Ca3(PO4)2.

We know the % composition of a white powder. Determine if this powder is common table sugar.

Find the % composition of Ca3(PO4)2.1. Calculate the molar mass

2. Calculate the percent of each element in a mole of the substance

For Ca: 3 x 40.078 = 120.23 g/mole

For P: 2 x 30.974 = 61.95 g/mole

For O: 8 x 15.999 = 127.99 g/mole

For Ca3PO4: 310.17 g/mole

Percent composition

Find the % composition of Ca3(PO4)2.1. Calculate the molar mass

2. Calculate the percent of each element in a mole of the substance

Ca: 120.24 g/mole

P: 30.97 g/mole

O: 64.00 g/mole

Ca3PO4:

310.17 g/mole

120.24100

310.17

30.97100

310.

%

%

%

38.77%

9.98%

20.6

17

64.00100

310.173%

Ca

P

O

Percent composition



Two types of problems

Find the % composition of Ca3PO4.


1.05 g0.16 g1.29 g

2.50 g

C:H2:O2:

Total of unknown:

A white powder can be broken down into 1.05 g of C, 0.16 g of H2, and 1.29 g of O2. Is this powder common table sugar, also known as sucrose (C12H22O11)?

1. Add up the individual mass measurements to get the total mass

2. Calculate the percent composition of the unknown

3. Compare with the percent composition of sucrose

Percent composition

Total of unknown: 2.50 g

1.05100

2.50

0.16100

2.50

42.0%

6.4%

%

%

%1.29

100 515

.6%2. 0

C

H

O





Percent composition





12.01 144.13 /

1.0079 22.17 /

15.999 175.99 /

: 342

:

:

:

12

22

11

.29 /

C

H

O

g mole

g mole

g mole

Molar mass g mole

Percent composition

For sucrose:





144.13100

342.29

22.17100

342.

%

%

%

42.1%

6.5%

51.

29

175.99100

342.294%

C

H

O

For sucrose:

Percent composition


144.13100

342.29

22.17100

342.

%

%

%

42.1%

6.5%

51.

29

175.99100

342.294%

C

H

O

% composition of unknown:

% C: 42.0%% H: 6.4%% O: 51.6%

% composition of sucrose:

YES!The percent composition is very close,

so the unknown is probably sugar

Percent composition

Empirical formulas

ClNa

NaCl Cl

Na

The empirical formula is the one with the simplest ratio

Na6Cl6ClNa

NaCl Cl

NaClNa NaCl

1:1 ratio6:6 ratio

Calculating an empirical formula1. Convert grams to moles

2. Simplify the mole ratio

3. Write the formulaAssume you have a sample that is 0.504 g hydrogen and 4.00 g oxygen.

Empirical formulas

2

1

:0.5

:

00

0.250

0.250

0.250

H

O

10.504

1.00.500

0.

1

14.00

16.000

:

25:

H

O

moleg

g

moleg

g

moles

moles

smallest number of moles

H2O

2.0

1.

0.04:

:

66

0.023

0.0230

0.023

Cu

O

1: 2.96 0.0466

63.55

1: 4.00 0.023

15.999

moleCu g moles

g

moleO g moles

g

Empirical formulas

A jar of powder is labeled copper oxide, but you do not know whether the copper is Cu+ or Cu2+. After taking a small sample you find that it is made from 2.96 g of copper and 0.37 g of oxygen. What is the correct name and formula for the ionic compound in that jar?

1. Convert grams to moles


3. Write the formula

Cu2O

Empirical formulas


Cu2OCu+

Cu+

O2–

+2 –2

Cu2+

Cu2+

O2–

+4 –2

Copper(I) oxide

Calculating an empirical formula1. Convert grams to moles


3. Write the formulaAssume you have a sample that is 0.504 g hydrogen and 4.00 g oxygen.

Empirical formulas

2

1

:0.5

:

00

0.250

0.250

0.250

H

O

10.504

1.00.500

0.

1

14.00

16.000

:

25:

H

O

moleg

g

moleg

g

moles

moles

smallest number of moles

H2O

2.0

1.

0.04:

:

66

0.023

0.0230

0.023

Cu

O

1: 2.96 0.0466

63.55

1: 4.00 0.023

15.999

moleCu g moles

g

moleO g moles

g

Empirical formulas


1. Convert grams to moles


3. Write the formula

Cu2O

Empirical formulas


Cu2OCu+

Cu+

O2–

+2 –2

Cu2+

Cu2+

O2–

+4 –2

Copper(I) oxide

Molecular formulas

The empirical formula can be the same as the molecular formula…

CH2O Formaldehyde

…but not always.

C6H12O6Glucose

CH2O

CH2O

Molecular formula

Empiricalformula

Molecular formulas

C6H12O6 GlucoseCH2O

Molecular formula

Empiricalformula

The molecular mass will always be equal to, or a multiple of, the empirical formula mass.

180.16 g/mole30.03 g/mole

x 6

x 6

Molecular formulas

CH

Molecular formula

Empiricalformula

13.018 g/mole

C?H?

78.11 g/mole

For CH: 12.011 + 1.0079 = 13.018 g/mole

Given the following empirical formula and molar mass, determine the molecular formula for CH (78.11 g/mole).

Molecular formulas

CH

Molecular formula

Empiricalformula

13.018 g/mole

C6H6

78.11 g/molex 6

The molecular formula is C6H6

Given the following empirical formula and molar mass, determine the molecular formula for CH (78.11 g/mole).



Two types of problems:

Find the % composition of Ca3(PO4)2.


The empirical formula can be the same as the molecular formula…

CH2O Formaldehyde

…but not always.

C6H12O6Glucose

CH2O

CH2O

Molecular formula

Empiricalformula

30 g/mole 180 g/molex 6

x 6

ch 8 - compounds & molecules 8.1 ionic compounds – fr 2-28 8.2 molecular compounds - fr 29-52...

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