“Water is H2O.”Today, we’ll see that water is the basis of how we measure mass.

Later this week, we will use H2O and some of its component atoms to exemplify molecules, compounds and atoms.

Matter has mass and occupies space.

A solution is a very fine mixture that eventually happens without mechanical agitation.

Definition of Matter: Details

•Matter: has mass and occupies space.

•Mass: how easy is it to accelerate the object. F = ma

•Acceleration: change in speed with time (dv/dt = d2x/dt 2 for you Calculus experts)

•Gravity provides a convenient, relatively constant, acceleration: F = mg where g = 9.8 m-s-2

Mass is measured indirectly• We could define one gram as the mass of

one cubic centimeter (or one cc) of water. • Then see how much a spring is

compressed with this mass on it under Earth’s gravity.

• For a good spring, an object that compresses it 2x more than one cubic cc of water must have 2 grams of mass.

• When you weigh something, you indirectly obtain its mass.

• The thing really being measured is a force, which has other units (kgms-2).

• We’ll practice with compound units soon.

1 cm

1 cm

1 cm

How would we measure mass without

Earth’s gravity?

Or no gravity at all?

http://spaceflight.nasa.gov/gallery/images/station/

View from insidethe spacestation.

Matter Occupies Space

What’s Space?

What does it mean to occupy the space?

In fact, for almost anything you can name, most of the space is not occupied!

Before we can understand that, we have to have ways to measure physical

properties.

Space is volume.

Our unit of length in chemistry is often the centimeter: one-hundredth of a meter.

Volume is length x width x height, or cm3

1 cm

1 cm

1 cm1 cm3 of water is one milliliter of water (one one-thousandth of a liter, and a liter is almost the same volume as a quart.)

S.I. Units* (Appendix C)

*The units have a bizarre history! On some other planet—did you know that there are billions of planets?—perhaps some other form of intelligent life is using altogether different units. Even here in the USA, we still dislike these units. Even most chemists prefer gram to kilogram, centimeter to meter, etc.

Length MeterMass KilogramTime SecondTemperature KelvinsNumber of something MoleElectric current AmpereLuminous intensity Candela

Prefixes—yes, you have to memorize them.

Prefix Example

Example means

Nano Nanometer 0.0000000001 m or 10-9 m

Micro Microliter 0.000001 L or 10-6 L

Milli Milligram 0.001 gram

Centi Centimeter 0.01 meter

Deci Deciliter 0.1 liters (= 100 milliliters, by the way)

Deka Dekameter 10 meters

Hecto Hectogram 100 grams

Kilo Kilometer 1000 meters (=0.6 miles, by the way)

Mega MegaHz 1000 cycles per second, once a very fast computer!

Giga GigaHz 1,000,000 = 106 cycles per second, now an OK computer (barely)

Sm

alle

r th

an

Larg

er

than

Properties with Compound Units

Density is the mass per unit volume. For example, the liquid mercury in a thermometer has a density of 13.6 grams per cubic centimeter.

Units of density: mL

g

cm

g

3

Billiard ball floating in mercury.

http://www.zyra.org.uk/mercury3.htm

Why do we care?1. Density is an

important, easily measured property that lets us gauge the purity of substances.

2. Heavy stuff sinks, so that tells us what we might have to do to, say, clean up a hazardous waste site. The Hanford Nuclear Site: 50

million gallons (more?) of contaminated wastes on the beautiful Columbia River. Pricetag to clean: $40,000,000,000 = $4 x 1010.(I have seen much higher estimates, too).

http://www.whistleblower.org/article.php?did=18&scid=28http://murray.senate.gov/hanfordcleanup/index.cfm

Another property with a compound unit: force.

Defining physical relation

F=ma

Mass in kilograms, kg

Acceleration, m/s2

Resulting physical unit

2sm

kg

Called a Newton, nt

Still more complex: pressure

Defining physical relation

P = F/A

Force, Newtons

Area, m2

Resulting physical unit

22

2

2 smkg

msm

kg

mnt

Called a Pascal, Pa

These aren’t the usual units of pressure here in the USA! 101,325 Pa = atmospheric pressure = 14.7 p.s.i.

Example: most cars use 32 p.s.i. in their tires. What’s that in Europe?

See notes for harder problems—a little like the team homeworks.

p.s.i. = pounds per square inch

Today’s Announcements

Chancellor’s Distinguished Lecture Series

“The Dark Side of the Universe: Beyond the Stars and the Starstuff We Are Made Of”

Professor Michael TurnerUniversity of Chicago5:00 p.m. 130 Nicholson Hall

Daily Evaluations

We made the quota last Thursday; bonus points will be added.

Biggest concern: Teams! PLEASE GIVE IT A CHANCE.

ConversionsFigure out the smaller unit. You will need a larger number of those. Example: Q. How many deciliters in 10 Liters? A. Deciliters is smaller, so you will need

more of them. Ten deciliters for each liter times 10 liters = 100 deciliters.

Or, you can do it very prim and proper (Appendix C of your

text)

deciliter 1Liter 1.0

1

1Liter 10

deciliter 1

.

1. Write the given: 10 liters2. Write the conversion: 1 deciliter = 0.1 liter3. Divide both sides of the conversion by right side: 4. Divide both sides of the conversion by left side:

5. Multiply the “given” from step 1 with whicheverform of the number one from steps 3-4

cancels the undesired unit.

deciliters 100Liter 0.1

deciliter 1Liter 10

Try to learn to line things out

deciliters 100Liter 0.1

deciliter 1Liter 10

Start by putting what you want at the left. Arrange conversion factors so as to cancel out the unit you do not want!

Despite the metric system, you must still to be able to convert between

different unit systems. Example: the smallest MOPAR V8 engine of 1965 was 273 cubic

inches. Today, we’d quote that in liters, but how many liters?

Reason it out: A liter is like one quart, a cubic inch is like your thumb.You will need a smaller number.

1 inch = 2.54 centimeters (Appendix C of text)

L 4.5mL 1000

L 1cm 1mL 1

in 1cm 2.54

in 273 3

33

You may find it much easier at first to do these problems one

step at a time.

33333 cm 16.4cm (2.54) inch 1

For example, just compute the conversion factor for in3 to cm3 first.

Cube both sides

cm 2.54 inch 1

Now what?

Problem for your team: estimate the volume of this

room in milliliters.

This will also teach us a bit about scientific notation.

Mapping: conversions that involve more than

multiplication & division. Example:

Centigrade to Fahrenheit

1.832F

Co

o

oC

oF

0

32

Slope = 1.8

32C1.8F oo

Kelvin temperature

273.15CK o

oC

K

0

273.15 Slope = 1

Converting oC to oF in your head 

Double the oC temperature.

Subtract 10%. 

Add 32. 

16 oC = 61 oF    July in Duluth or January in

Baton Rouge 

98.6 oF = 37 oC Body Temperature or

Summer in Dallas 

- 40 oF = - 40 oC Winter in Duluth, but hardly

the coldest day

100 oFRectal temperature of the

cow 

77 oC = 25 oC Room Temperature

77 K = -196.15 oC = -321 oF Liquid N2   

Facts of Life

Stop here?

Elements

If all the atoms in a given sample of "material" are

"the same" then the chemical is said to be an

elemental form. Actually, almost the same!

Another definition of elements

Difficult to purify further by the means available to a 1930’s chemist.

Example: •It is easy to break water down into oxygen and hydrogen. •It gets a lot harder after that. •Oxygen is an element. •Hydrogen is another element.

There are about 118 elements….some of them man-made.

This will become more and more clear asthe semester progresses.

Atoms: Trust me (for now)

The word means “indivisible” Atoms are NOT indivisible! Much effort went into cutting them

up to figure out how they work. We will cover that fascinating history

later.

We think atoms look like this

All the mass is here!

The light red spaceis mostly empty!

That is why almost everything is really empty!

Some elements exist as single atoms.

Example: Xe, Ne

www.theroadwanderer.net/ 66NMex/gallneon.htm

Some elements exist as arrays of atoms with undefined size.

Example: Carbon as diamond

http://www.phy.mtu.edu/nue/CubeHover_small.htmlhttp://www.phy.mtu.edu/nue/CubeHover_small.html

The 45.52 carat Hope Diamond

Example: Carbon as graphite (the little disk floating above

the cubical magnets, same stuff as pencil “lead”!)

Of huge interest to chemists, and almost nobody else, some elements

exist as molecules.Example: Hydrogen as H2

Molecules?

Molecules

Normal Oxygen, O2

Ozone, O3

Molecules can involve different types of atoms.

H2

O

A molecule is a compound, but not all compounds are

molecules.Molecule of water: Barring total destruction, as in electrolysis,these two hydrogens and the oxygen will stay with each other forever.

Sodium ion, Na+

Chloride ion, Cl-

A tiny chunk of the compound, sodium chloride. Not a molecule.

Learn to draw it yourself: http://www.chemguide.co.uk/atoms/structures/ionicstruct.htmlhttp://www.chemguide.co.uk/atoms/structures/ionicstruct.html

The difference between molecules and compounds is like the difference between marriage and dating.

Molecules = Atomic Marriage: you stay with a particular atom no matter what (barring real torture, such as electrocution—i.e. electrolysis—or something equally painful, like a chemical reaction).

Compounds = Atomic Dating: it’s a lot easier to break up and start seeing other atoms. Later, you might get back together with the original atom….but probably not. Thus, sodium chloride can be easily dissolved. If you dry out that saltwater solution, the sodium and chloride atoms will attach to different partners.

Different Representations of Molecules

A good time to check out the ACS

Molecule of the Week

ACS is the world’s largest scientific society: 118,452 members.

Daily Evaluation/Amusement

Conversions!Cows! Notes. Meanwhile, download

lectures!Do we need to know the m/s velocity

stuff?

Physical States of Matter: Physical vs. Chemical

Transformations •Big 3 are: Liquid, Solid, Gas•Other, more nebulous states exist: glass, liquid crystal •Ice to water to steam are physical transformations:  •no real change in chemical formula.•Water electrolysis to Hydrogen and Oxygen gas

is a chemical transformation: not only does

the formula change, but a molecule is broken. •In many practical operations, both physical and

chemical transformations take place.

Polymer liquid crystal: J. Chem. Phys., 111(4), 1746-1752 (1999).

Isomers (Iso=same; mers=parts)

Chemical EquationsChemists are good at converting one compound to another.  We have discovered a few rules about doing this:

1. The total mass is never changed.

2. Atoms are not changed or lost.  

3. How the atoms are arranged, and which partners they choose,

can change a lot.  

Balancing Chemical Equations

1 H2(g) + 1 Cl2(g) 2 HCl(g)

H atoms on left: 1x 2 = 2Cl atoms on left: 1 x 2 = 2

H atoms on right: 2 x 1 = 2Cl atoms on right: 2 x 1 = 2

Burning Hydrogen

2H2 + O2 2H2O

Ooops…The blue H atoms should be smaller than the orange O atoms.

Another Example

The decomposition of potassium chlorate to potassium chloride and oxygen: 

KClO3 KCl + O2

KCl Problem

Checkit, Dammit!2 KClO3 ----» 2 KCl + 3 O2

AtomOn left

sideOn right

sideK 2 x 1 = 2 2 x 1 = 2

Cl 2 x 1 = 2 2 x 1 = 2

O 2 x 3 = 63 x 2 = 6

The Secret of Balancing (and life)

Do it a lot! DRILL!(You have lots of homework like

this.)Keep trying!  PERSIST!

It is trial and error, so GUESS!

Try This Now!

___CH4 + ___O2 ___H2O + ___CO2

Compute the force in Newtons exerted by your body mass when you stand on a scale.

Blank Screen

Spare Stuff from Appendix

Precision vs. Accuracy

It is possible to be consistently wrong.

Significant FiguresWrong Right Why

1.867 + 2 = 3.867 1.867 + 2 = 4 Addition/Subtraction: use least precise places

1.867 + 2.000 = 4 1.867 + 2.000 = 3.867 "

1.867 x 2 = 3.734 1.867 x 2 = 4 Multiply/Divide: use smallest number of significant figures

1.867 / 2.000 = 1 1.867/2.000 = 0.9355 "

What does this read?

Exponential (Scientific) Notation

Avogadro’s number (the number of H2O molecules in 18 grams of

water):602,000,000,000,000,000,000,000 = 6.02 x 1023

Age of universe in seconds (somebody’s guess):300,000,000,000,000,000 s = 3 x 1017

Learn to type exponents efficiently into your calculator! (The E or EEX button)

Sample problems

How many clock cycles does a 3GHz Pentium computer go through in one day?

How many molecules of water in a nanogram of water?