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S. Ensign, matter and measurements1

What is “Chemistry”?

The study of the properties of materials and the changes that materials undergo

The study of the composition, properties, and transformations of matter

The study of the properties of materials and the changes that materials undergo

The study of the composition, properties, and transformations of matter


Many societal issues require an understanding of chemistry to comprehend and evaluate

• Why do most scientists believe global warming is caused by the burning of fossil fuels? What is the greenhouse effect?

• What is the ozone layer, what results in its depletion, and why is it important?

• What is acid rain and what causes it?• What health hazards are present in the air we breathe, water

we drink, and food we eat? Should we be worried about them?

• What are the health benefits/risks of different diets and foods (oats, antioxidants, selenium, tomatoes, butter vs. margarine)

• Should we fluoridate our water? What are the pros and cons?• Are alternate medical practices beneficial, worthless, or

dangerous? Will an ionic footbath remove toxins from our bodies? Will magnets align our energy fields?


How does chemistry relate to other sciences?• Materials: properties and changes• Some materials you may encounter in your profession:

Computer chips- silicon and ceramics Computer science

Geologic specimens: rocks, fossils Geology

Viruses, bacteria, monkeys Biochemistry, biology, medicine

Polymers, ceramics Engineering

Energy sources, petroleums Chemistry, engineering

Air bag design Engineering

Pharmaceuticals Pharmacy, medicine

Pollutants, toxins, carcinogens Toxicology, medicine

Fertilizers, pesticides Agriculture

Explosives Military, engineering


The hierarchy of scientific learning….

• What’s at the top?• What’s at the bottom?• What’s most

important?• What’s least

important?

Biology

Chemistry

Mathematics

Physics

Philosophy


Chemistry is an “experimental science”The “Scientific Process”

Make observations, design and perform experiments

Find patterns, trends, laws

Formulate and test “hypotheses”

Develop a “theory”


Lecture outline, Chapter 11. Introduction to matter2. Substances and mixtures3. Elements and compounds4. Physical and chemical properties and

changes5. Units of measurement6. Exponential notation and prefixes7. Uncertainty in measurement8. Dimensional analysis


NGC 4449 galaxy , Image Credit: NASA, ESA, A. Aloisi (STScI/ESA), and The Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

The universe consists largely of matter and energy

2


Matter- The physical material of the universe. Anything that occupies space and has mass.

Energy- Much more complicated with multiple levels of definitions.

•Potential to perform work (Ch. 5)•Potential energy (Ch. 5)•Kinetic energy (Ch. 5)•Heat (Ch. 5)•Radiant energy (Ch. 6)•Chemical energy (Ch. 5)•Free energy (Ch. 19)•Electrical energy (Ch. 20)•Nuclear energy (Ch. 21)


The three physical states of matter

Physical state

Defined volume?

Defined shape?

Compress/expand?

Gas

Liquid

Solid

Classifying matter: Substance• Matter with fixed composition and distinct

properties.– Water, sucrose, salt, oxygen, glycerol, aspirin, iron


Classifying matter: Mixture• A combination of 2 or more substances

– Kool-aid, air, salt water, steel– Each substance in the mixture retains its own

chemical identity and properties– May be heterogeneous or homogeneous and in any

physical state• Heterogeneous: non-uniform• Homogeneous: uniform throughout (a solution)

– Can be separated into constituent substances by physical means (evaporation, heating, filtering, etc)



Matter

Pure substance

Mixture

Not separable by physical means

Separable by physical means

Heterogeneousmixture

Homogeneous mixture (solution)

Non-uniformthroughout

Uniformthroughout

ex: granite, oil and vinegar salad dressing, frozen mixed vegetables

Gatorade, air, salt water, antifreeze, gasoline, brass

Subdividing matter

Ex: water, sucrose, salt, oxygen, glycerol, aspirin, iron

Can pure substances be broken down further by other means?

The building blocks of matter• All matter is comprised of very small, individual

particles called “atoms”• Atoms can be chemically connected (bonded)

to each other• Atoms are composed of smaller “subatomic”

particles called protons, neutrons and electrons• Atoms are distinguished from each other by the

number of subatomic particles (more specifically, protons) they are built from

• A chemical element is a pure substance containing only one type of atom


•The basic unit of an element is an atom, defined by the number of protons it was built from

•Atoms of the same or different type can be “bonded”(joined) together to form “molecules”. A chemical bond is an attraction between two atoms that holds them together

•An element is a substance consisting of only one type of atom, whether individual or bonded atoms


Elements, atoms, and molecules

C OH NHydrogen (1) Carbon (6) Nitrogen (7) Oxygen (8)

H H O O C C C C C C C C CC C C C C C C C C

O OO O O O


Elements and their symbols• ~114 known elements• Some common elements,

their one or two letter abbreviations (“symbols”), and the number of protons they contain:

Hydrogen H 1Helium He 2Carbon C 6Calcium Ca 20Chlorine Cl 17Nitrogen N 7Oxygen O 8Sulfur S 16Silicon Si 14Iodine I 53Iron Fe 26


Elemental composition (by mass) of:

The earth’s crust

The human body

The universe

•A substance composed of two or more different elements joined by chemical bond(s)•The elemental composition (whole number ratio of atoms) is always the same for a pure compound


Compound

OHH

C OO H NH

HCH

HHH C

H

HHH O


Physical and. chemical changesPhysical change- changes that affect the stateor form but not composition of a substance

Chemical change (reaction)- The combining or decomposing of substance(s), by breaking and forming chemical bonds, to form new substance(s) that have new compositions


Changes of state:


Changes of form by rearranging atoms:


Chemical decomposition:

OHH

OHH HH HH

O O


Chemical combination:

HH

HHH N

H

HN N

HH

H NH

H


Chemical combination:

OC C OOOHH HH


Elements cannot be decomposed into simpler substances by chemical means

(chemical reactions)Compounds Elements

OHH

H NH

H

HH O O

N NHH


Matter

Pure substance

Mixture

Not separable by physical means

Separable by physical means

Heterogeneousmixture

Homogeneous mixture (solution)

Non-uniformthroughout

Uniformthroughout

Element Compound

Can be broken down by chemical means

Cannot be broken down to simpler components by chemical means

ex: water, sucrose, carbon dioxide, glycerol, ammonia

ex: hydrogen, oxygen, gold, lead, iron, nitrogen, carbon

ex: granite, oil and vinegar salad dressing, frozen mixed vegetables

Gatorade, air, salt water, antifreeze, gasoline, brass

Subdividing matter


Physical and chemical properties are used to describe and differentiate different types of matterPhysical properties- properties that can be measured without changing the basic identity of the substance

Chemical properties- the way a substance may change or “react” to form other substances


Physical properties-

Chemical properties-

Physical changes-

Chemical changes-


Gauging our progress:1. Introduction to matter2. Substances and mixtures3. Elements and compounds4. Physical and chemical properties and

changes5. Units of measurement6. Exponential notation and prefixes7. Uncertainty in measurement8. Dimensional analysis


Units of measurementThe “systeme international” (SI)

The seven SI base unitsPhysical measurement Name AbbreviationLength Meter mMass Kilogram kgTime Second s (sec)Temperature Kelvin KAmount of substance Mole molElectric current Ampere ALuminous intensity Candela cd


Familiarize yourselves with these 5 base units.

Note that the unit of mass is the only base SI unit using a prefix (kilo, which means x 1000)


The use of prefixes and/or exponential notation are useful when working with very

large and very small numbersThe seven SI base unitsPhysical measurement Name AbbreviationLength Meter mMass Kilogram kgTime Second s (sec)Temperature Kelvin KAmount of substance Mole molElectric current Ampere ALuminous intensity Candela cd

Dealing with very large and very small numbers

• Scientific (exponential) notation: a x 10b

where “a” is a real number and “b” is an integer

• Metric prefix: An affix placed before a unit of measure to indicate a decadic multiple or fraction of the unit– 1 kilogram means 1000 grams– 1 millimeter means 1/1000 of a meter



Writing numbers in exponential notation

• Numbers greater than one:– Move decimal point to the left the number of

places required to give a number between 1 and 10

– The number of places decimal was moved is the exponent “n”

Ex: Write 96,418 in exponential notation1234

The decimal was moved 4 places, so the number is written 9.6418 x 104


Writing numbers in exponential notation• Numbers less than one:

– As for numbers > 1, but move decimal point “n” places to the right

– The exponent is “- n”

Ex: Write 0.00594 in exponential notation1 2 3

The decimal was moved 3 places, so the number is written 5.94 x 10-3


Know the meaning of these 8 prefixes

Prefixes commonly used with SI units in chemistryPrefix Abbre-

viationMeaning(10n)

Meaning (Decimal)

Example

Mega M 106 1,000,000 1 Ms = 106 s Kilo k 103 1,000 75 kg = 75 x 103 g =

75,000 g

Deci d 10-1 0.1 1 dL = 0.1 litersCenti c 10-2 0.01 1 cm = 0.01 mMilli m 10-3 0.001 1 mg = 0.001 g = 10-3 gMicro μ 10-6 0.000001 1 μs = 10-6 sNano n 10-9 0.000000001 700 nm = 700 x 10-9 m

= 7 x 10-7 mPico p 10-12 0.000000000001 5 ps = 5 x 10-12 s

Meaning of some base SI units important to chemistry

• Length (duh)• Mass• Time (duh)• Temperature• Amount


Mass ≠ weight• Mass: a measure of the magnitude of

gravitational force experienced by and exerted by an object

• Weight: the gravitational force felt by an object when on earth

• Mass is measured based on weight on earth• My mass on earth, the moon, and in outer

space is 70 kg. • My weight is 70 kg on the earth, 12 kg on the

moon, and 0 kg in outer space S. Ensign, matter and measurements

37

Temperature• A measure of the direction and magnitude of

heat flow; measure of “hotness” or “coldness” of an object

• Temperature scales and units:K (kelvin): the SI unit

°C (degrees celsius): a common scientific unit

°F (degrees fahrenheit): the conversational unit



)32(95

−⋅= FC oo

3259

+⋅= CF oo

Don’tmemorize

Figure source: Wikimedia commons, Author User:Gringer http://commons.wikimedia.org/wiki/File:Thermometer_CF.svg

Relationship between temperature in °C and °F

Why use kelvin to measure temperature?

• Temperature is referenced relative to the lowest possible attainable temperature (0 K)

• K = 273.15 + °C (memorize)• Absolute zero = 0 K (-273.15 °C)• Water freezes at 273.15 K (0 °C)• Water boils at 373.15 K (100 °C)• Body temperature is ~37 °C (310.15 K)



Derived SI units• Units of measurement obtained by multiplication

and/or division of appropriate base units• Examples:

– Speed– Area – Volume– Density


Length = 10 cm

Length = 10 cm

Length = 10 cm

Area = l x l = 100 cm2

Length = 10 cm

Length = 10 cm

Volume = l x l x l = 1000 cm3 = 1000 mL = 1 L

By definition, 1 mL = 1 cm3


Intensive properties- do not depend on sample size

Extensive properties- do depend on sample size

Intensive or extensive? Temperature, density, volume, mass, heat content, electrical conductivity


Uncertainty in measurements• Exact numbers: values known exactly;

infinitely precise• Inexact numbers: obtained from

measurements. values have some uncertainty and are subject to error

The whole history of physics proves that a new discovery is quite likely lurking at the next decimal place. ~F.K. Richtmeyer


Precision vs. accuracy• Precision: a measure of how closely

individual measurements agree with each other

• Accuracy: a measure of how closely individual measurements agree with the “correct” value

Accuracy?

Precision?


Accuracy and Precision

√√√


You weigh out 10 pennies using a balance with a digital readout that looks like this:

The readout reads:

Thus, you report the mass of the pennies as 26.3 grams. BUT– what if they really weigh:

26.27 g?26.33 g?26.34 g?26.29 g?

26.3 ± 0.1 g

2 6 3

certain uncertain

Certain + uncertain = # of significant figuresUsing the number obtained from this balance, we can say we

have 26.3 grams of pennies, but not 26.30 grams!


What’s the difference between4.0 g and 4.00 g?


Measuring devices are subject to differing degrees of uncertainty in making measurements

100. mL? 100.0 mL? 100.0 mL?


1) All nonzero digits are significant2) Zeros between nonzero digits are

significant3) Zeros to the left of the first nonzero

digit are not significant4) Zeros that fall both at the end of a

number and to the right of the decimal point are significant

5) When a number ends in zeros but contains no decimal point, the zeros may or may not be significant

457 2.5

1.03 1.004

0.02 0.002

0.02003.000

130 10,300

Significant figure rules


Value Rules Sig figs0.036653 1, 3 57.2100 x 10-3 1,4 572,100 km 5 3,4 or 5$25.03 n/a exact76.600 kg 1, 4 54.50200 x 103 g 1, 4 63000 nm 5 1,2,3 or 40.0300 ml 1,3,4 318 students n/a exact

How many significant figures are in the following numbers?

(1) All nonzero digits are significant

(2) Zeros between nonzero digits are significant

(3) Zeros to the left of the first nonzero digit are notsignificant

(4) Zeros that fall both at the end of a number and to the right of the decimal point are significant

(5) When a number ends in zeros but contains no decimal point, the zeros may or may not be significant


Significant figures in calculations• x, ÷ result must have no more sig. figs

than the measurement with the fewest sig. figs.

• +, - result should be reported to same number of decimal places as that of the term with the least number of decimal places


Rounding numbers


Significant figures in calculations• x, ÷ result must have no more sig. figs than

the measurement with the fewest sig. figs.• +, - result should be reported to same number

of decimal places as that of the term with the least number of decimal places


Significant figures in calculationsFor multistep calculations, carry at least one (and preferably more) additional digits past the number of known significant figures for intermediate answers/values

(Don’t introduce errors due to “premature rounding”)


Dimensional analysis• Convert a quantity described in one unit to

an equivalent quantity described in a different unit

Conversion factor: a ratio that correctly expresses the relationship between different numbers that have different units

Units are treated as numbers- multiply and divide them as numbers


Conversion factor: a ratio that correctly expresses the relationship between different numbers that have different units


Units are treated as numbers- multiply and divide them as numbers


You travel to Germany on vacation and rent a Porsche™ at the airport. The gas tank is full. After driving 100. km, you stop and fill the tank. It takes 16 liters and lots of euros, because the europeans have ridiculously high gas taxes.

You want to know what mileage you are getting in miles per gallon. You curse the E. C. for not adopting american units of distance and volume. Why must they be so stubborn?

Use the following conversion factors to determine your gas consumption in miles/gallon:

1 km = 0.6214 miles1 gallon = 3.78 liters


Prefixes commonly used with SI units in chemistryPrefix Abbre-

viationMeaning(10n)

Conversion factor relative to unit with prefix

Conversion factor relative to base unit

Mega M 106 106 g/Mg 10-6 Mg/gKilo k 103 103 g/kg 10-3 kg/g

Deci d 10-1 10-1 g/dg 101 dg/gCenti c 10-2 10-2 g/cg 102 cg/gMilli m 10-3 10-3 g/mg 103 mg/gMicro μ 10-6 10-6 g/μg 106 μg/gNano n 10-9 10-9 g/ng 109 ng/g

Pico p 10-12 10-12 g/pg 1012 pg/g

Note how units with prefixes are used as conversion factors in two orientations. Work with whichever orientation you are most comfortable with.


You have a lab beaker with a volume of 800. ml.

(1) What is the volume in cm3?

(2) What is the volume in liters?

(3) What is the volume in m3 ?


The “cup” is a volume widely used for cooking in the U.S. If 1.00 cup of olive oil has a mass of 205 g, what is the density of the oil in g/ml?1 cup = 225 ml


Ethylene glycol is the main constituent of antifreeze. You need 500. ml of ethylene glycol. But you have no volumetric measuring device. You do have a balance. What mass of ethylene glycol gives 500. ml? densityEG = 1.1135 g/ml


Express 1 ng in units of μg.Or in other words,

How many μg are in1 ng?

what is chemistry - utah state universityion.chem.usu.edu/~ensigns/chem1210/lectureoverheads/1...

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