NOTES: Introduction to Chemistry

CHEMISTRY!

● CHEMISTRY = the study of the composition of matter, its chemical and physical changes, and the energy changes that accompany these changes.

The Nature of Science

● Scientific law versus theory:

-Scientific law: a summary of an observed natural event

-Scientific theory: a well-tested explanation of a natural event; supported by EVIDENCE

The Way Science Works…

● Science involves critical thinking, or applying logic and reason to observations and conclusions.

● Observation vs. Inference-Observation: description of what you see, hear,

taste, feel, smell

-Inference: the conclusion you draw as a result of an observation (not always correct!!)

Variables and Controls● A variable is anything that can change in an

experiment.

-Independent variable: The variable being changed or controlled by the scientist.

-Dependent variable: The variable being measured or observed by the scientist.

● A controlled experiment tests only one variable at a time.

The Scientific Method:A series of logical steps to follow in order to solve problems.

• OBSERVE• FORMULATE A QUESTION• FORM A HYPOTHESIS• DESIGN AND CONDUCT AN EXPERIMENT• MAKE OBSERVATIONS• RECORD AND ANALYZE DATA• DRAW CONCLUSIONS• FORMULATE NEW QUESTIONS and

CONTINUE CYCLE

Making Measurements

● Measurements are made in this class using SI units.

● LENGTH (m): distance between 2 points

● VOLUME (L): space occupied

● MASS (g): the amount of matter in an object

● WEIGHT (N): the force with which gravity pulls on a quantity of matter

Graph - visual representation of data1) title2) x and y axis labeled3) units for both the x and y axis4) scale is evenly and correctly spaced for data5) legend when appropriate

Organizing DataData is organized and presented in tables, charts, and graphs.

LINE GRAPH: best for displaying data that change.

**a.k.a. a SCATTER PLOT!!– Independent Variable: x-axis– Dependent variable: y-axis

Temperature Increase of a Beaker of Water

250

300

350

400

450

0 50 100 150 200 250 300 350 400

Time (sec)

Tem

pera

ture

(K)

BAR GRAPH: useful when you want to compare data for several individual items

Leading Causes of Death in 2000

300

233

107 9857

0

50

100

150

200

250

300

350

HeartDisease

Cancer Diabetes Accidents HomicideNu

mb

er

of

De

ath

's p

er

100,

000

Pe

op

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PIE CHART: ideal for displaying data that are parts of a whole.

Favorite Television Shows among Teens

45%

30%

20%

4%

1%

Friends

Will and Grace

Frasier

Dawson's Creek

Other

MATTER = ANYTHING WITH MASS AND VOLUME

(CHAPTER 2, sections 2.1 & 2.4)

Matter

Pure Substances

Mixtures

Elements

Compounds

Homogeneous

Heterogeneous

Everything that is, is made up of matter.

From the very large...

To the very small...

Properties of Matter can be…

● Extensive properties: depend on the AMOUNT of matter

-Example: Mass, Volume

● Intensive properties: depend on the TYPE of matter

-Example: Absorbancy, Density

STATES OF MATTER:

● SOLID

● LIQUID

● GAS

SOLIDS:

● Definite shape?

● YES

● Definite volume?

● YES

● Molecules in a solid are tightly packed and constantly vibrating.

LIQUIDS:

● Definite shape?● NO

● Definite volume?● YES

● Some liquids flow more easily than others. The resistance of a liquid to flow is called viscosity. – Honey has a high viscosity compared to water.

GASES:

● Definite shape?● NO

● Definite volume?● NO

● The particles in a gas are spread very far apart, but can be compressed by pumping them into a restricted volume.

Physical Properties:

● Physical properties: characteristics that can be observed without changing the identity of the substance.

● Examples: -mass -melting pt.-volume -boiling pt.-color -magnetism-shape -texture-density

Physical Changes:

● Physical change: a change in the physical form or properties of a substance that occurs without a change in composition.

● Examples:-melting -bending-freezing -tearing-grinding -crushing-dissolving -boiling

Phase Changes:● Changes in phase are examples of

physical changes.

● Melting: solid liquid

● Freezing: liquid solid

● Vaporization: liquid gas

● Condensation: gas liquid

● Sublimation: solid gas

Chemical Properties:

● Chemical property: describes a substance’s ability to change into a different substance.

● Examples: -flammability

-reactivity

Chemical Changes:

● Chemical change: occurs when a substance changes composition by forming one or more new substances. (bonds are broken and bonds are formed)

What is a Chemical Reaction?

● Chemical Reaction – one or more substances change into new substances

● Process involves reactants and products

● Reactant – a starting substance in a chemical reaction

● Product – a substance formed in a chemical reaction

What is a Chemical Reaction?

● Example:

Nitrogen and hydrogen gas can react to form ammonia under certain conditions.

Reactants Yield Products

N2(g) + H2(g) NH3(g)

How Can You Tell Whether or Not a Chemical Reaction Has Taken Place?

● Chemical Change – alters a given material by changing its chemical composition

● Examples: burn, rust, decompose, corrode, explode

Other Indicators of a CHEMICAL CHANGE:

-change in heat -change in color-change in odor-light is given off-formation of a gas-formation of a solid-irreversibility

Evaporation is a physical change

Breaking is a physical change.

Boiling is a change of state, and therefore a

physical change!

Rusting is a Chemical Change

Burning is a Chemical Change

CONSERVATION:

● Law of Conservation of Matter (Mass): in a physical change or a chemical reaction, matter is neither created nor destroyed; it is conserved

Matter MUST be conserved; it’s the LAW!