What is Chemistry - Utah State Universityion.chem.usu.edu/~ensigns/chem1210/lectureoverheads/1...
Transcript of What is Chemistry - Utah State Universityion.chem.usu.edu/~ensigns/chem1210/lectureoverheads/1...
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
S. Ensign, matter and measurements2
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?
S. Ensign, matter and measurements3
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
S. Ensign, matter and measurements4
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
S. Ensign, matter and measurements5
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”
S. Ensign, matter and measurements6
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
S. Ensign, matter and measurements7
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
S. Ensign, matter and measurements8
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)
S. Ensign, matter and measurements9
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
S. Ensign, matter and measurements10
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)
S. Ensign, matter and measurements11
S. Ensign, matter and measurements12
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
S. Ensign, matter and measurements13
•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
S. Ensign, matter and measurements14
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
S. Ensign, matter and measurements15
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
S. Ensign, matter and measurements16
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
S. Ensign, matter and measurements17
Compound
OHH
C OO H NH
HCH
HHH C
H
HHH O
S. Ensign, matter and measurements18
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
S. Ensign, matter and measurements24
Elements cannot be decomposed into simpler substances by chemical means
(chemical reactions)Compounds Elements
OHH
H NH
H
HH O O
N NHH
S. Ensign, matter and measurements25
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
S. Ensign, matter and measurements26
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
S. Ensign, matter and measurements27
Physical properties-
Chemical properties-
Physical changes-
Chemical changes-
S. Ensign, matter and measurements28
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
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
S. Ensign, matter and measurements30
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)
S. Ensign, matter and measurements31
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
S. Ensign, matter and measurements32
S. Ensign, matter and measurements33
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
S. Ensign, matter and measurements34
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
S. Ensign, matter and measurements35
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
S. Ensign, matter and measurements36
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
S. Ensign, matter and measurements38
S. Ensign, matter and measurements39
)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)
S. Ensign, matter and measurements40
S. Ensign, matter and measurements41
Derived SI units• Units of measurement obtained by multiplication
and/or division of appropriate base units• Examples:
– Speed– Area – Volume– Density
S. Ensign, matter and measurements42
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
S. Ensign, matter and measurements43
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
S. Ensign, matter and measurements44
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
S. Ensign, matter and measurements45
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
S. Ensign, matter and measurements47
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!
S. Ensign, matter and measurements49
Measuring devices are subject to differing degrees of uncertainty in making measurements
100. mL? 100.0 mL? 100.0 mL?
S. Ensign, matter and measurements50
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
S. Ensign, matter and measurements51
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
S. Ensign, matter and measurements52
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
S. Ensign, matter and measurements54
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
S. Ensign, matter and measurements55
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
S. Ensign, matter and measurements56
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”)
S. Ensign, matter and measurements57
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
S. Ensign, matter and measurements58
Conversion factor: a ratio that correctly expresses the relationship between different numbers that have different units
S. Ensign, matter and measurements59
Units are treated as numbers- multiply and divide them as numbers
S. Ensign, matter and measurements60
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
S. Ensign, matter and measurements61
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.
S. Ensign, matter and measurements62
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 ?
S. Ensign, matter and measurements63
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
S. Ensign, matter and measurements64
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