Study of the structure of matter -”the science that seeks to understand the behavior of matter by studying the behavior of atoms and molecules”

From the smallest (atoms) to the largest (materials) Atomic or molecular properties affect material properties Study of the changes matter undergoes (reactions)

What is Chemistry?

Chapter 1: Matter, Measurement, and Problem

Solving

Learning Outcomes • Determining Physical and Chemical Changes and Properties

• Converting between Temperature Scales; Fahrenheit, Celsius, and Kelvin

• Calculating the Density of a Substance

• Reporting Scientific Measurements to the Correct Digit of Uncertainty

• Working with Significant Figures

• Using Conversion Factors

• Solving Problems Involving Equations

Atoms vs. Molecules

http://emergentchaos.com/archives/2009/09/atoms-photographed.html

Free atoms are not common in nature. Can you name a few materials that may have free atoms? Can you name a material that is not made up of molecules?

Matter

Note: It may be useful to get a periodic table you like and always bring it to class and lab

Atoms and Molecules

• Elements – A substance that cannot be decomposed into simpler

substances. Contains one kind of atom (H, Na, O) • Basic building block of matter • Period table

• Atoms – The smallest part of an element that can exist

chemically • All matter can be described in terms of the interactions of

atoms with each other • Molecules

– One of the fundamental units forming a chemical compound

• Combination of two or more atoms.

ATOMS are the basic building blocks of everything

ELEMENTS are the kinds of atoms that we can have

Atoms can join together - they form bonds together - to make MOLECULES

H C

Structure of

diamond

Ethane – C2H6

Atoms and Molecules

Problem Solving

1. Observe a problem 2. Write down the facts related to problem 3. Analyze the data, identify the type of

problem to be solved, and outline a plan to answer the problem

4. Carry out your plan to obtain tentative result (experiement)

5. Evaluate answer as reasonable or not -(for science problems)

Problem Solving A large portion of solving problems in chemistry requires math. You MUST be good at math to succeed in chemistry To understand a problem, you have to be well acquainted with the material. Read the chapters BEFORE class. Lecture should be a review used for clarification Chemistry questions are often regarded as ”tricky” They usually involve more than one concept at once You cannot memorize chemistry questions. You have to apply yourselves.

Three terms often used interchangeably are “hypothesis," “law," and "theory” - but not in science!

Hypothesis: A tentative interpretation or explanation of the observations

Observed, but not proved (working assumption) Can be supported or refuted by experimentation or

continued observation Dalton's Hypothesis: All matter is composed of atoms

If a hypothesis successfully passes many tests, it can form the basis

for a theory

Hypothesis

• Law: A brief statement that summarizes past observations and predicts future ones.

• Scientific laws describe things. They do not explain them.

• Based on a series of similar experimental observations

Newton’s law of gravity predicts the behavior of falling objects, but it does not explain WHY it happens.

Law of conservation of mass

Easier – think of a scientific law as a principle instead

Law

Theory

• Theory: A well established, tested explanation of basic natural phenomena

– Verified multiple times – A theory can be modified – One scientist cannot create a theory; only a hypothesis – More complex and dynamic than a law - tries to explain

not only what nature does…but WHY

The atomic theory states (among other things) that all matter is composed of atoms

1. What is the best definition of the term "theory," as it is used in science? a) A theory is a guess or hunch about something that has occurred in nature. b) A theory is a comprehensive set of ideas explaining a phenomenon in nature. c) A theory is based on verifiable laws and can be proven true. d) A theory is a hypothesis that uses laws and observation to make an assumption. 2. While speaking to a colleague, a scientist makes the following statement: "I propose

that Bald Eagle eggs in northern Maine will have thinner shells than those from birds in southern Alaska due to increased levels of pesticides in the water." This statement is a

a) theory b) law c) conclusion d) hypothesis 3. Which statement below correctly identifies the difference between laws and theories? a) Laws describe phenomena, while theories explain why phenomena exist. b) Laws are a statement of fact, while theories are a statement of opinion. c) Laws explain why phenomena exist, while theories explain how. d) Laws are a prediction of phenomena, while theories are an explanation.

Matter: Anything that occupies space and has mass. Substance: The specific matter you are talking about.

Different Physical States of Matter: Solid – Rigid - Fixed shape and volume. Atoms/Molecules remain

in fixed place and only vibrate. Liquid – Relatively incompressible fluid - Fixed volume but no

fixed shape. Atoms/molecules tightly packed, but can move past one another allowing flow.

Gas – Easily compressible fluid - No fixed shape or volume.

Atoms/Molecules are widely spaced.

The Classification of Matter

Physical States of Matter. Molecular representations of a solid, liquid, and a gas

Classifying Matter According to its Composition

Definitions for Vocabulary

• Pure Substances – A kind of matter that cannot be separated into other

kinds of matter by any physical process • NaCl and Water are substances, but salt water is not

• Compounds

– A substance formed by the combination of elements in fixed proportions by a chemical reaction

• Cannot be separated by physical means • Water is a compound

• Mixtures

– A material that can be separated by physical means into two or more substances

• Variable composition – example: salt water • Air is a mixture (O2 and N2)

Mixtures

Heterogeneous – A mixture that consists of physically distinct

parts, each with different properties

Homogeneous – A mixture that has uniform properties

throughout (solution)

Mixture :a substance consisting of two or more substances mixed together (not in fixed proportions and not with chemical bonding)

Mixtures can be separated by physical means Is this a homogeneous or heterogeneous mixture?

Mixtures

Homogeneous vs. Heterogeneous

“homogenous means that it's all mixed together exactly the same; heterogeneous means that it's all jumbled together with different clumps and different amounts of things in different places.”

Element Compound or Mixture?

For each box determine whether you are looking at : 1- a solid, liquid, or gas 2 - elements, compounds, or mixtures 3 - a heterogeneous or homogeneous mixture.

Physical and Chemical Changes

What is the difference between physical and chemical changes?

Physical Change: Change that only alters state or appearance

• Reversible • No new compounds are formed • Can separate mixtures by physical means

Boiling of a liquid Melting of a solid Dissolving a solid in a liquid

Chemical Change: A change in which one or more kinds of matter are transformed into a new kind of matter or several new kinds of matter

• Irreversible • New compounds are formed • To recover reactants requires chemical

reactions

Physical and Chemical Changes

Chemical reactions like - combustion - oxidation

We characterize or identify materials by their various properties

• Physical Property – A characteristic that can be observed for a

material without changing its chemical identity • Melting point, boiling point, density, smell, color

• Chemical Property

– A characteristic of a material involving its changing chemical composition

• Flammability, acidity, toxicity, corrosiveness • Can usually be identified when there is an

observable change: such as in color, or if heat is given off

Potassium is a soft, silver-colored metal that melts at 64°C. It reacts vigorously with water, with oxygen, and with chlorine. Identify all of the physical and the chemical properties given in this description

• Physical – Soft, silver-colored metal, melts at 64°C

• Chemical

– Reacts vigorously with water, reacts with oxygen, reacts with chlorine

Units of Measure

English System – inches, yards, pounds, miles, pints Metric System (called the International System of Units –S.I) - centimeters, meters, grams, liters

To record a measurement you need both the measured number and the unit

SI Base Units

SI Prefixes Multiple of Base Unit

Prefix Symbol

106 mega M 103 kilo k 10-1 deci d 10-2 centi c 10-3 milli m 10-6 micro µ 10-9 nano n 10-12 pico p

The advantage of the metric system is that it is a decimal system

Know your prefixes, and their relative size to the base unit!

1m = 1 x 109 nm 1cm = 1 x 101 mm 1 km = 1 x 103 m

Notice how I only wrote positive exponents? If you put the ‘1’ by the larger prefix, this will always be the case. (there are more little things in a big thing)

Conversions will be easier if you always follow this convention.

SI Units

Write the following without scientific notation • 5.89 x 10-12 s

• 0.2010 m

• 2.56 x 10-9 g

• 6.05 x 103 m

Temperature

The Celsius scale is the temperature scale in general scientific use*.

– However, the SI base unit of temperature is the kelvin (K), a unit based on the absolute temperature scale.

– The conversion from Celsius to Kelvin is simple since the two scales are simply offset by 273.15°.

K = °C + 273.15

*When doing calculations for gases we always convert to kelvin!

Temperature

• The Fahrenheit scale is at present the common temperature scale in the United States. – The conversion of Fahrenheit to Celsius, and

vice versa, can be accomplished with the following formulas

°C = °F - 32 1.8 °F = 1.8 (°C) + 32

Comparison of Temperature Scales

50.°F = 10.°C = 283 K

SI Derived Units

• Units created by combination of SI base units – The SI unit for speed is meters per second, or m/s.

– Volume is defined as length cubed and has an SI unit of

cubic meters (m3).

– Traditionally, chemists have used the liter (L), which is a unit of volume equal to one cubic decimeter.

• 1L = 1 dm3 • 1cc = 1 cubic centimeter = 1mL

Derived Units • The density of an object is its mass per unit volume,

Mass is given in g

Volume is given in: – mL for liquids : g/mL – cm3 for solids : g/cm3 – L for gases : g/L

VolumeforUnitsSImassforUnitsSI

Vmd ==

Is the copper penny more or less dense than the mercury?

The Reliability of a Measurement The number of digits in a reported measurement indicated the certainty associated with that measurement. More digits = more certainty Fewer digits = less certainty The number of digits you record for a measurement is not something each person chooses depending on how they feel…it is tied directly to the equipment used to measure and everyone using that specific equipment will always report to the same certainty.

The Reliability of a Measurement

• Precision – How close a series of measurements are to one

another – Reproducibility

• You did 5 measurements and obtained the same value

• Accuracy – Refers to the closeness of a single measurement

to its true value • You measured a 5cm long piece of metal and

determined it had a length of 4.99cm

Poor accuracy Good precision

Poor accuracy Poor precision

Good accuracy Good precision

What about Good accuracy and poor precision?

Reporting to the Correct Number of Digits

Look at the ruler and tell me the length of the steel rod

There are 10 divisions between 9 and 10 The rod is slightly larger than 9.1cm, but much less than 9.2cm Mentally divide the smallest space (0.1cm) into 10 equal parts We know the length is 9.1x cm, we just have to estimate the x 9.12 cm ± 0.01cm

What is the length of the nail to the correct number of significant figures?

5.75 cm ± 0.05cm or 5.70 cm ± 0.05cm

Significant figures are those digits in a measured number that include all certain (definite) digits plus a final one having some uncertainty

Significant Figures

In measuring with the ruler, the first two digits (9.1) are certain

The next digit was estimated, therefore it had some uncertainty

Number of significant figures refers to the number of digits that indicate the precision of the value

9.12cm - 3 sig. figs 9.123cm - 4 sig. figs

Significant Figures

Significant Figures To count the number of significant figures in a measurement, observe the following rules:

1. All nonzero digits are significant. 3.333

2. Zeros between significant figures are significant. 3.003

3. Zeros preceding the first nonzero digit are not significant. 0.03333

4. Zeros to the right of the decimal after a nonzero digit are significant. 3.300

Significant Figures

5. Zeros at the end of a nondecimal number may or may not be significant.

Use scientific notation to avoid ambiguity

• 300 cm – can not tell # of sig figs • 3.00x102 - Three sig figs

Sometimes a line or decimal is used: 1200 = 2 sig figs 1200. = 4 sig figs 1200 = 3 sig figs

If the number has a decimal in it: Like reading; go to the right until you hit a non-zero number. Everything after that is significant.

Exact Numbers

Have NO uncertainty ‘infinite sig figs’ 1 – accurate counting of objects [eg. five chairs] 2 – defined quantities [10 mm in 1 cm or 2.54cm in an inch] 3 – integral numbers [to halve something, divide by 2]

Significant Figures in Calculations

When multiplying and dividing measured quantities, give as many significant figures as the least found in the measurements used.

8.71 x 0.0301 / 0.031 =

Significant Figures in Calculations

When adding or subtracting measured quantities, give the same number of decimals as the least found in the measurements used. 0.71 + 92.2 =

Keeping track of sig figs when adding and/or subtracting is difficult. Many students frequently lose points because they do not understand how to keep track of sig figs when adding or subtracting. You cannot simply look at the calculation and know how many sig figs the answer has!

Significant Figures in Calculations

When you have both kinds of operations in a calculation follow the rules as you go step by step Calculate the following : (847.89 - 847.73) x 14673 847.89 – 847.73 = 0.16 0.16 x 14673 = 2347 BUT ONLY TWO SIG FIGS!! Best to change to scientific notation 0.16 x 14673 = 2.3x103 (= 2300)

Significant Figures in Calculations

Calculate the following : (847.82 - 847.73) x 14673

How many significant figures does the answer to the following calculation have?

12.3456-12.3447

Rounding

• Dropping of nonsignificant digits in a calculation result and adjusting the last digit

Round 1.2151 to 3 Sig. Figs.

• Look at the leftmost digit to be dropped • 5 or greater = add one • Less than 5 = do not change

Rounding gives 1.22 to 3 sig. figs.

Rounding example: 1.2151 rounded to three significant

figures is: 1.22 1.2143 rounded to three significant

figures is: 1.21

Examples

How many significant figures should be reported for the difference between 235.2497 and 235.22?

What is the best answer to the following expression: (4.9800-4.9680) x 0.2500 ?

Perform the following calculation and round your answer to the correct number of significant figures:

28.7289189146

×..

Perform the following calculation and round your answer to the correct number of significant figures: 59.1453.0 −

Perform the following calculation and round your answer to the correct number of significant figures:

421.0456.0 −

Perform the following calculation and round your answer to the correct number of significant figures:

)421.0456.0(35.92 −

Units: Dimensional Analysis

• Dimensional analysis (or the factor-label method) is the method of calculation in which one carries along the units for quantities. – Suppose you simply wish to convert 20 yards to feet.

– Note that the units have cancelled properly to give the

final unit of feet. Always use this method for conversion calculations in this class.

feet 60 yard 1 feet 3 yards 20 = × feet 60 yard 1 feet 3 yards 20 = ×

Units: Dimensional Analysis

• The ratio (3 feet/1 yard) is called a conversion factor. – The conversion-factor method may be used to

convert any unit to another, provided a conversion equation exists.

– Relationships between U.S. units and metric units will be given on tests.

Relationships of Some U.S. and Metric Units

Length Mass Volume

1 in = 2.54 cm 1 lb = 0.4536 kg 1 qt = 0.9464 L 1 yd = 0.9144 m 1 lb = 16 oz 4 qt = 1 gal

1 mi = 1.609 km 1 oz = 28.35 g

1 mi = 5280 ft

Unit Conversion

• Sodium hydrogen carbonate (baking soda) reacts with acidic materials such as vinegar to release carbon dioxide gas. Given an experiment calling for 0.348 kg of sodium hydrogen carbonate, express this mass in milligrams.

x 0.348 kg x 10 3 g

1 kg

10 3 mg

1 g = 3.48 x 10 5 mg x x 0.348 kg x

10 3 g

1 kg

10 3 mg

1 g = 3.48 x 10 5 mg 0.348 kg x

10 3 g

1 kg

10 3 mg

1 g = 3.48 x 10 5 0.348 kg x mg

10 3 g

1 kg

10 3 mg

1 g = 3.48 x 10 5 mg

Unit Conversion

• Suppose you wish to convert 0.547 lb to grams. – Note that 1 lb = 453.6 g, so the conversion factor

from pounds to grams is 453.6 g/1 lb. Therefore,

g 248 lb 1

g 453.6 lb 547 . 0 = × g 248 lb 1

g 453.6 lb 547 . 0 = ×