Chapter 1 1.1 to 1.5 Chemical Foundations. Chapter 1 Table of Contents Return to TOC Copyright ©...

Chapter 11.1 to 1.5

Chemical Foundations

Chapter 1

Table of Contents

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Copyright © Cengage Learning. All rights reserved

1.1 Chemistry: An Overview

1.2 The Scientific Method

1.3 Units of Measurement

1.4 Uncertainty in Measurement

1.5 Significant Figures and Calculations

Measurement andMeasurement andSignificant FiguresSignificant Figures

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Chapter OnePrentice Hall © 2005 Hall © 2005General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry

Getting Started: Some Key Terms

• Chemistry is the study of the composition, structure, and properties of matter and of changes that occur in matter.

• Matter is anything that has mass and occupies space.٭ Matter is the stuff that things are made of.

Section 1.1

Chemistry: An Overview

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• A main challenge of chemistry is to understand the connection between the macroscopic world that we experience and the microscopic world of atoms and molecules.

• You must learn to think on the atomic level.

Section 1.1


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Atoms vs. Molecules - Fundamental Principle #1

• Matter is composed of tiny particles called atoms.• Atom: smallest part of an element that is still that element.• Molecule: Two or more atoms joined and acting as a unit.

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Key Terms

• Molecules are larger units in which two or more atoms are joined together.٭ Examples: Water consists of molecules, each

having two atoms of hydrogen and one of oxygen.٭ Oxygen gas consists of molecules, each having

two atoms of oxygen.

Water molecule

Oxygen molecule

Section 1.1


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Oxygen and Hydrogen Molecules

• Use subscripts when more than one atom is in the molecule.

Section 1.1


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A Chemical Reaction - Fundamental Principle #2

• One substance changes to another by reorganizing the way the atoms are attached to each other.

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Key Terms

• Composition – the types of atoms and their relative proportions in a sample of matter.

• The composition of water is two parts (by atoms) of hydrogen to one part (by atoms) of oxygen.

• The composition of water is 11.2% hydrogen by mass, 88.8% oxygen by mass.٭ (Why the difference? Because hydrogen atoms and

oxygen atoms don’t have the same mass!)٭ More on mass composition in section 3.5

Section 1.2

The Scientific Method

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• Science is a framework for gaining and organizing knowledge.

• Science is a plan of action — a procedure for processing and understanding certain types of information.

• Scientists are always challenging our current beliefs about science, asking questions, and experimenting to gain new knowledge.– Scientific method is needed.

Science

Section 1.2


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Steps of the Scientific Method

• Process that lies at the center of scientific inquiry.

Steps in the Scientific MethodSteps in the Scientific Method

1.1. ObservationsObservations-- quantitative - numerical data quantitative - numerical data

(5 g)(5 g)- - qualitative - descriptive data qualitative - descriptive data

(blue)(blue)2.2. Formulating hypothesesFormulating hypotheses

- - possible explanation for the possible explanation for the observationobservation

3.3. Performing experimentsPerforming experiments- - gathering new information to gathering new information to

decidedecide whether the hypothesis is validwhether the hypothesis is valid

Section 1.2


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Scientific Models

• Summarizes what happens.

Law

Theory (Model)

• An attempt to explain why it happens.• Set of tested hypotheses that gives an overall explanation

of some natural phenomenon.

Hypothesis

• A possible explanation for an observation.

Outcomes Over the Long-TermOutcomes Over the Long-Term

Theory (Model)Theory (Model)- - A set of tested hypotheses that give A set of tested hypotheses that give an overall explanation of some natural an overall explanation of some natural phenomenon.phenomenon.

Natural LawNatural Law-- The same observation applies to The same observation applies to many different systemsmany different systems

Scientific method.l Theories have predictive value.l The true test of a theory is if it can

predict new behaviors.l If the prediction is wrong, the theory

must be changed.l Theory- whyl Law – howl Law – equation of how things change

Law vs. TheoryLaw vs. Theory

A A lawlaw summarizes what happens summarizes what happens

A A theorytheory (model) is an attempt to explain (model) is an attempt to explain whywhy it happens. it happens.

Einstein's theory of gravity describes gravitational forces in terms of the curvature of spacetime caused by the presence of mass

Nature of MeasurementNature of Measurement

Part 1 - Part 1 - numbernumberPart 2 - Part 2 - scale (unit)scale (unit)

Examples:Examples:20 20 gramsgrams

6.63 x 106.63 x 10-34-34 Joule·secondsJoule·seconds

A measurement is a quantitative A measurement is a quantitative observation consisting of 2 parts:observation consisting of 2 parts:

The Fundamental SI UnitsThe Fundamental SI Units (le Système International, SI)(le Système International, SI)

SI UnitsSI Units

Celsius & KelvinCelsius & Kelvin

SI Prefixes Common to ChemistrySI Prefixes Common to Chemistry

Prefix Unit Abbr. Exponent

Mega M 106

Kilo k 103

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro μ 10-6

Nano n 10-9

Pico p 10-12

Section 1.3

Units of Measurement

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Prefixes Used in the SI System

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Volume

• The derived unit of volume (space taken up by an object) is the cubic meter (m3).

• A very common unit of volume, not SI but still used, is the liter (L).

• The milliliter (mL; 0.001 L) is also used, as is the cubic centimeter (cm3).

• 1 mL = 1 cm3.• There are about five mL

in one teaspoon.

Deriving the Liter

l Liter is defined as the

volume of 1 dm3

l gram is the mass of 1 cm3

Mass and Weightl Mass is measure of resistance to

change in motion l Weight is force of gravity.l Sometimes used interchangeablyl Mass can’t change, weight can

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Mass and Time

• Mass is the quantity of matter in an object; weight is a force.

• The base unit of mass is the kilogram (kg; 1000 g); it already has a prefix.

• A 1-L bottle of soft drink weighs about a kilogram.

• Commonly used mass units include the gram and the milligram (mg; 0.001 g).

• The SI base unit of time is the second (s).

• Smaller units of time include the millisecond (ms), microsecond (µs), and nanosecond (ns).

• Larger units of time usually are expressed in the nontraditional units of minutes, hours, days, and years.

Uncertainty in MeasurementUncertainty in Measurement

A digit that must be A digit that must be estimatedestimated is called is called uncertainuncertain. A measurement . A measurement alwaysalways has has some degree of uncertainty.some degree of uncertainty.

Measurements are performed with instruments No instrument can read to an infinite number of decimal places

Section 1.4

Uncertainty in Measurement

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Measurement of Volume Using a Buret

• The volume is read at the bottom of the liquid curve (meniscus).

• Meniscus of the liquid occurs at about 20.15 mL. Certain digits: 20.15 Uncertain digit: 20.15

Precision and AccuracyPrecision and AccuracyAccuracyAccuracy refers to the agreement of a particular refers to the agreement of a particular value with the value with the truetrue value. value.

PrecisionPrecision refers to the degree of agreement refers to the degree of agreement among several measurements made in the same among several measurements made in the same manner.manner.

Neither accurate nor

precise

Precise but not accurate

Precise AND accurate

Types of ErrorTypes of Error

Random ErrorRandom Error (Indeterminate Error) - (Indeterminate Error) - measurement has an equal probability measurement has an equal probability of being of being highhigh or or lowlow..

Systematic ErrorSystematic Error (Determinate Error) - (Determinate Error) - Occurs in the Occurs in the same directionsame direction each time each time (high or low), often resulting from poor (high or low), often resulting from poor technique or incorrect calibration. technique or incorrect calibration. This This can result in measurements that are can result in measurements that are precise, but not accurate.precise, but not accurate.

Uncertainty-Systemic Error

l Systematic error- same direction each time

l Want to avoid thisl Bad equipment or bad technique.l Better precision implies better accuracyl You can have precision without

accuracyl You can’t have accuracy without

precision (unless you’re really lucky).

Rules for Counting Significant Rules for Counting Significant Figures - DetailsFigures - Details

Nonzero integersNonzero integers always count always count as significant figures.as significant figures.

34563456 has has

44 sig figs sig figs..


ZerosZeros-- Leading zeros Leading zeros do not count do not count as significant figures.as significant figures.

0.04860.0486 hashas

33 sig figs.sig figs.


ZerosZeros-- Captive zerosCaptive zeros

always count as significant always count as significant figures.figures.

16.0716.07 hashas



ZerosZerosTrailing zeros Trailing zeros are significant are significant only if the number contains a only if the number contains a decimal point.decimal point.

9.3009.300 hashas



Exact numbersExact numbers have an infinite have an infinite number of significant figures.number of significant figures.

11 inchinch == 2.542.54 cm, exactlycm, exactly

9 pencils (obtained by counting) - EXACT

Sig Fig Practice #1Sig Fig Practice #1How many significant figures in each of the following?

1.0070 m 1.0070 m 5 sig figs5 sig figs

17.10 kg 17.10 kg 4 sig figs4 sig figs

100,890 L 100,890 L 5 sig figs5 sig figs

3.29 x 103.29 x 1033 s s 3 sig figs3 sig figs

0.0054 cm 0.0054 cm 2 sig figs2 sig figs

3,200,000 3,200,000 2 sig figs2 sig figs

Rules for Significant Figures in Rules for Significant Figures in Mathematical OperationsMathematical Operations

Multiplication and DivisionMultiplication and Division:: # sig figs in the result equals the # sig figs in the result equals the

number in the least precise number in the least precise measurement used in the measurement used in the calculation.calculation.

6.38 x 2.0 =6.38 x 2.0 =

12.76 12.76 13 (2 sig figs)13 (2 sig figs)

Sig Fig Practice #2Sig Fig Practice #2

3.24 m x 7.0 m3.24 m x 7.0 m

CalculationCalculation Calculator says:Calculator says: AnswerAnswer

22.68 m22.68 m22 23 m23 m22

100.0 g ÷ 23.7 cm100.0 g ÷ 23.7 cm33 4.219409283 g/cm4.219409283 g/cm33 4.22 g/cm4.22 g/cm33

0.02 cm x 2.371 cm0.02 cm x 2.371 cm 0.04742 cm0.04742 cm22 0.05 cm0.05 cm22

710 m ÷ 3.0 s710 m ÷ 3.0 s 236.6666667 m/s236.6666667 m/s 240 m/s240 m/s

1818.2 lb x 3.23 ft1818.2 lb x 3.23 ft 5872.786 lb·ft5872.786 lb·ft 5870 lb·ft5870 lb·ft

1.030 g ÷ 2.87 mL1.030 g ÷ 2.87 mL 2.9561 g/mL2.9561 g/mL 2.96 g/mL2.96 g/mL

Rules for Significant Figures in Rules for Significant Figures in Mathematical OperationsMathematical Operations

Addition and SubtractionAddition and Subtraction: The : The number of decimal places in the number of decimal places in the result equals the number of decimal result equals the number of decimal places in the least precise places in the least precise measurement.measurement.

6.8 + 11.934 =6.8 + 11.934 =

18.734 18.734 18.7 18.7 ((3 sig figs3 sig figs))

Sig Fig Practice #3Sig Fig Practice #3

3.24 m + 7.0 m3.24 m + 7.0 m

CalculationCalculation Calculator says:Calculator says: AnswerAnswer

10.24 m10.24 m 10.2 m10.2 m

100.0 g - 23.73 g100.0 g - 23.73 g 76.27 g76.27 g 76.3 g76.3 g

0.02 cm + 2.371 cm0.02 cm + 2.371 cm 2.391 cm2.391 cm 2.39 cm2.39 cm

713.1 L - 3.872 L713.1 L - 3.872 L 709.228 L709.228 L 709.2 L709.2 L

1818.2 lb + 3.37 lb1818.2 lb + 3.37 lb 1821.57 lb1821.57 lb 1821.6 1821.6 lblb

2.030 mL - 1.870 mL2.030 mL - 1.870 mL 0.16 mL0.16 mL 0.160 mL0.160 mL

Complex sig figsl What if it uses both addition and

multiplication rules?l Round when you change rules.

• Measure your textbook using the four rulers provided and fill in the table in your Course Guide.

• Justify the precision for each of your measurements, and the number of significant figures in each of your calculations.

React 1

Section 1.5

Significant Figures and Calculations

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• Example 300. written as 3.00 × 102

Contains three significant figures.

• Two Advantages Number of significant figures can be easily

indicated. Fewer zeros are needed to write a very large or very

small number.

Exponential Notation

Copyright © Houghton Mifflin Company. All rights reserved. 1–24

• You have water in each graduated cylinder shown. You then add both samples to a beaker. How would you write the number describing the total volume? What limits the precision of this number?

React 2

Section 1.5


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Concept Check

You have water in each graduated cylinder shown. You then add both samples to a beaker (assume that all of the liquid is transferred).

How would you write the number describing the total volume?

3.1 mL

What limits the precision of the total volume?

48

Section 1.5


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CH. 1 ASSIGNMENTS

CW/HW: CH 1 ASSIGNED PROBLEMS: CW/HW: Ch1 - pg. 31-35 #19, 25, 27, 29, 31, 33, 35, 41, 45, 49bc, 51abc, 55, & (67-81 odd) due next Monday.

*Activity: Metric Puzzles if time permits &/or Sig. Figs. activity Bingo #2/game/or other act.

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