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 data 1) title 2) x and y axis labeled 3) units for both the x and y axis 4) scale is evenly and correctly spaced for data 5) legend when appropriate Organizing Data Data 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

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

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

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 N 2 (g) + H 2 (g)  NH 3 (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: -c hange 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!