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1
Foundations of Chemistry
A quick review!
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2
Steps in the Scientific Method
1.1. ObservationsObservations
quantitativequantitative
qualitativequalitative
2.2. Formulating hypothesesFormulating hypotheses
possible explanation for the observationpossible explanation for the observation
3.3. Performing experimentsPerforming experiments
gathering new information to decidegathering new information to decide
whether the hypothesis is validwhether the hypothesis is valid
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3
Outcomes Over the Long-Term
Theory (Model)Theory (Model)
A set of tested hypotheses that give anA set of tested hypotheses that give an overall explanation of some overall explanation of some
natural natural phenomenon.phenomenon.
Natural LawNatural Law
The same observation applies to manyThe same observation applies to many different systemsdifferent systems
Example - Law of Conservation of Example - Law of Conservation of MassMass
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4
The Fundamental Steps of the Scientific
Method
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5
The Various Parts of the Scientific
Method
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6
Law v. Theory
A A lawlaw summarizes what happens; summarizes what happens;
A A theorytheory (model) is an attempt to (model) is an attempt to explain explain whywhy it happens. it happens.
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7
Nature of Measurement
Measurement - quantitative observation consisting of Measurement - quantitative observation consisting of 2 parts2 parts
Part 1 - numberPart 1 - number Part 2 - scale (unit)Part 2 - scale (unit)
Examples:Examples:20 grams20 grams
6.63 6.63 Joule seconds Joule seconds
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8
International System(le Système International)
Based on metric system and units Based on metric system and units derived from metric system.derived from metric system.
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9
The Fundamental SI Units
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10
Measurement of Volume
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Common Types of Laboratory Equipment Used to Measure Liquid Volume
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Measurement of Volume Using a BuretThe volume is read at the bottom of the liquid curve (called the meniscus).
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13
Uncertainty in Measurement
A digit that must be A digit that must be estimatedestimated is called is called uncertainuncertain. A . A measurementmeasurement always has always has some degree of uncertainty.some degree of uncertainty.
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14
Precision and Accuracy
Accuracy Accuracy refers to the agreement of a refers to the agreement of a particular value with theparticular value with the true true value.value.
PrecisionPrecision refers to the degree of agreement refers to the degree of agreement among several elements of the same among several elements of the same quantity.quantity.
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15
The Difference between Precision and Accuracy
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Types of Error
Random Error Random Error (Indeterminate Error) - (Indeterminate Error) - measurement has an equal probability of measurement has an equal probability of being high or low.being high or low.
Systematic Error Systematic Error (Determinate Error) - (Determinate Error) - Occurs in the Occurs in the same directionsame direction each time (high each time (high or low), often resulting from poor technique.or low), often resulting from poor technique.
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17
Rules for Counting Significant Figures - Overview
1.1. Nonzero integersNonzero integers
2.2. ZerosZeros
leading zerosleading zeros
captive zeroscaptive zeros
trailing zerostrailing zeros
3.3. Exact numbersExact numbers
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18
Rules for Counting Significant Figures - Details
Nonzero integersNonzero integers always count as always count as significant figures.significant figures.
3456 3456 has has
4 4 sig figs.sig figs.
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Rules for Counting Significant Figures - Details
ZerosZerosLeading zerosLeading zeros do not count as do not count as
significant figures.significant figures.
0.04860.0486 has has
33 sig figs. sig figs.
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20
Rules for Counting Significant Figures - Details
ZerosZeros Captive zerosCaptive zeros always count as always count as
significant figures.significant figures.
16.07 16.07 hashas
4 4 sig figs.sig figs.
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21
Rules for Counting Significant Figures - Details
ZerosZeros Trailing zerosTrailing zeros are significant only are significant only
if the number contains a decimal if the number contains a decimal point.point.
9.3009.300 has has
44 sig figs. sig figs.
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22
Rules for Counting Significant Figures - Details
Exact numbersExact numbers have an infinite number of have an infinite number of significant figures.significant figures.
11 inch = inch = 2.54 2.54 cm, exactlycm, exactly
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23
Rules for Significant Figures in Mathematical Operations
Multiplication and Division: Multiplication and Division: # sig figs in # sig figs in the result equals the number in the least the result equals the number in the least precise measurement used in the calculation.precise measurement used in the calculation.
6.38 6.38 2.0 = 2.0 =
12.76 12.76 13 (2 sig figs)13 (2 sig figs)
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24
Rules for Significant Figures in Mathematical Operations
Addition and Subtraction: Addition and Subtraction: # sig figs in the # sig figs in the result equals the number of decimal places result equals the number of decimal places in the least precise measurement.in the least precise measurement.
6.8 + 11.934 =6.8 + 11.934 =
22.4896 22.4896 22.5 (3 sig figs)22.5 (3 sig figs)
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25
Dimensional Analysis
Proper use of “unit factors” leads to proper Proper use of “unit factors” leads to proper units in your answer.units in your answer.
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26
Temperature
Celsius scale =Celsius scale =CCKelvin scale = KKelvin scale = K
Fahrenheit scale =Fahrenheit scale =FF
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27
The Three Major Temperature
Scales
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Normal Body Temperature on the Fahrenheit, Celsius,
and Kelvin Scales
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29
Temperature
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30
Density
Density Density is the mass of substance per unitis the mass of substance per unit
volume of the substance:volume of the substance:
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31
Matter:Matter: Anything occupying Anything occupying
space and having mass.space and having mass.
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Classification of Matter
Three States of Matter:Three States of Matter:
Solid: rigid - fixed volume and shapeSolid: rigid - fixed volume and shape
Liquid: definite volume but assumes the Liquid: definite volume but assumes the shape of its containershape of its container
Gas: no fixed volume or shape - assumes Gas: no fixed volume or shape - assumes the shape of its containerthe shape of its container
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33
Types of Mixtures
Mixtures have variable composition.Mixtures have variable composition.
AA homogeneous mixturehomogeneous mixture is a solution (for is a solution (for example, vinegar)example, vinegar)
AA heterogeneous mixtureheterogeneous mixture is, to the naked is, to the naked eye, clearly not uniform (for example, a eye, clearly not uniform (for example, a bottle of ranch dressing)bottle of ranch dressing)
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34
Pure Substances
Can be isolated by separation methods:Can be isolated by separation methods:
ChromatographyChromatography
FiltrationFiltration
DistillationDistillation
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35
Simple Laboratory Distillation Apparatus
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Element:Element: A substance that cannot be A substance that cannot be decomposed into simpler substances by decomposed into simpler substances by chemical means.chemical means.
Compound:Compound: A substance with a A substance with a constant composition that can be constant composition that can be broken down into elements by broken down into elements by chemical processes.chemical processes.
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37
The Organization
of Matter
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38
The Early History of ChemistryThe Early History of Chemistry
Before 16th CenturyAlchemy: Attempts (scientific or otherwise) to
change cheap metals into gold
17th CenturyRobert Boyle: First “chemist” to perform
quantitative experiments
18th CenturyGeorge Stahl: Phlogiston flows out of a burning
material.Joseph Priestley: Discovers oxygen gas,
“dephlogisticated air.”
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39
Law of Conservation of MassLaw of Conservation of Mass
Discovered by Antoine Lavoisier
Mass is neither created nor destroyed
Combustion involves oxygen, not phlogiston
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Other Fundamental Chemical LawsOther Fundamental Chemical Laws
A given compound always contains exactly the same proportion of elements by mass.
Carbon tetrachloride is always 1 atom carbon per 4 atoms chlorine.
Law of Definite Proportion
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Other Fundamental Chemical LawsOther Fundamental Chemical Laws
When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.
The ratio of the masses of oxygen in H2O and H2O2 will be a small whole number (“2”).
Law of Multiple Proportions
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42
Dalton’s Atomic Theory (1808)Dalton’s Atomic Theory (1808)
Each element is made up of tiny particles called atoms.
The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.
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Dalton’s Atomic Theory(continued)
Dalton’s Atomic Theory(continued)
Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms.
Chemical reactions involve reorganization of the atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.
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44
Representation of some of Gay-Lussac’s Experimental Results on Combining Gas Volumes
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45
Representation of Combining Gases at the Molecular Level
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Avogadro’s Hypothesis (1811)Avogadro’s Hypothesis (1811)
5 liters of oxygen
5 liters of nitrogen
Same number of particles!
At the same temperature and pressure, equal At the same temperature and pressure, equal volumes of different volumes of different gasesgases contain the same contain the same number of particles.number of particles.
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47
Early Experiments to Characterize the AtomEarly Experiments to
Characterize the Atom
J. J. Thomson - postulated the existence of electrons using cathode ray tubes.
Ernest Rutherford - explained the nuclear atom, containing a dense nucleus with electrons traveling around the nucleus at a large distance.
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48
Deflection of Cathode Rays by an Applied Electric Field
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The Plum Pudding Model of the Atom
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50
Diagram of the Millikan Apparatus
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51
Rutherford’s Experiment on particle Bombardment of Metal Foil
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Expected and Actual Results of Rutherford’s Experiment
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The Modern View of Atomic Structure
The Modern View of Atomic Structure
electrons
protons: found in the nucleus, they have a positive charge equal in magnitude to the electron’s negative charge.
neutrons: found in the nucleus, virtually same mass as a proton but no charge.
The The atomatom contains: contains:
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The Mass and Change of the Electron, Proton, and NeutronThe Mass and Change of the
Electron, Proton, and Neutron
Particle Mass (kg) Charge
Electron 9.11 10 31 1
Proton 1.67 10 27 1+
Neutron 1.67 10 27 0
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55
Nuclear Atom Viewed in Cross Section
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The Chemists’ Shorthand: Atomic Symbols
The Chemists’ Shorthand: Atomic Symbols
K Element Symbol39
19
Mass number
Atomic number
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Two Isotopes of Sodium
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Chemical BondsChemical Bonds
The forces that hold atoms together in compounds. Covalent bonds result from atoms sharing electrons.
Molecule: a collection of covalently-bonded atoms.
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59
Two Isotopes of Sodium
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60
The Structural Formula for Methane
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61
Sodium Chloride
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The Chemists’ Shorthand:Formulas
The Chemists’ Shorthand:Formulas
Chemical Formula:
Symbols = types of atoms
Subscripts = relative numbers of atoms
CO2
Structural Formula:
Individual bonds are shown by lines.
O=C=O
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IonsIons
Cation: A positive ion
Mg2+, NH4+
Anion: A negative ion
Cl, SO42
Ionic Bonding: Force of attraction between oppositely charged ions.
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Periodic TablePeriodic TableElements classified by:
properties
atomic number
Groups (vertical)
1A = alkali metals
2A = alkaline earth metals
7A = halogens
8A = noble gases
Periods (horizontal)
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The Periodic Table
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Naming CompoundsNaming Compounds
1. Cation first, then anion
2. Monatomic cation = name of the element
Ca2+ = calcium ion
3. Monatomic anion = root + -ide
Cl = chloride
CaCl2 = calcium chloride
Binary Ionic Compounds:Binary Ionic Compounds:
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Naming Compounds(continued)
Naming Compounds(continued)
metal forms more than one cation
use Roman numeral in name
PbCl2
Pb2+ is cation
PbCl2 = lead (II) chloride
Binary Ionic Compounds (Type II):Binary Ionic Compounds (Type II):
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Common Cations and Anions
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Naming Compounds(continued)
Naming Compounds(continued)
Compounds between two nonmetals
First element in the formula is named first.
Second element is named as if it were an anion.
Use prefixes
Never use mono-
P2O5 = diphosphorus pentoxide
Binary compounds (Type III):Binary compounds (Type III):
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Flowchart for Naming Binary Compounds