Matter Chemistry I: Chapter 2. What is Chemistry? Textbook Definition: The science of matter and the changes it undergoes. Dictionary Definition: The.

MatterMatterChemistry I: Chapter 2

What is Chemistry?

• Textbook Definition: The science of matter and the changes it undergoes.

• Dictionary Definition: The science of the composition, structure, properties, and reactions of matter, especially of atomic and molecular systems.

Chemistry

• “The central science” – Why?–Because most of the phenomena that occur in the world involve chemical changes

What is Matter?

–the material of the universe–has mass and volume

»mass: the amount of matter in an object

»volume: the amount of space an object takes up

The Nature of MatterThe Nature of MatterThe Nature of MatterThe Nature of Matter

Chemists are interested in the nature of Chemists are interested in the nature of matter and how this is related to its matter and how this is related to its atoms and molecules.atoms and molecules.

GoldGold MercuryMercury

Chemistry & MatterChemistry & Matter• We can explore the We can explore the

MACROSCOPIC MACROSCOPIC world — what we world — what we can see — can see —

• to understand the to understand the PARTICULATE PARTICULATE (MICROSCOPIC)(MICROSCOPIC) worlds we worlds we cannot see.cannot see.

• We write We write SYMBOLSSYMBOLS to describe to describe these worlds.these worlds.

A Chemist’s View of A Chemist’s View of WaterWater

H2O (gas, liquid, solid)

MacroscopicMacroscopicMacroscopicMacroscopic

SymbolicSymbolicSymbolicSymbolicParticulateParticulateParticulateParticulate

A Chemist’s ViewA Chemist’s View

2 H2(g) + O2 (g) --> 2 H2O(g)

MacroscopicMacroscopicMacroscopicMacroscopic

SymbolicSymbolicSymbolicSymbolicParticulateParticulateParticulateParticulate

The Macroscopic View

The states of matter:SolidsLiquidsGasesPlasma

Kinetic Nature of MatterKinetic Nature of MatterKinetic Nature of MatterKinetic Nature of MatterMatter consists of atoms and Matter consists of atoms and

molecules in constant random molecules in constant random motion.motion.

STATES OF MATTERSTATES OF MATTERSTATES OF MATTERSTATES OF MATTER• SolidsSolids — have rigid shape, fixed volume. — have rigid shape, fixed volume.

External shape can reflect the atomic and External shape can reflect the atomic and molecular arrangement.molecular arrangement.– Reasonably well understood.Reasonably well understood.

• LiquidsLiquids — have no fixed shape and may — have no fixed shape and may not fill a container completely. not fill a container completely. – Not well understood.Not well understood.

• GasesGases — expand to fill their container. — expand to fill their container. – Good theoretical understanding.Good theoretical understanding.

OTHER STATES OF MATTEROTHER STATES OF MATTEROTHER STATES OF MATTEROTHER STATES OF MATTER

• PLASMAPLASMA — an electrically charged — an electrically charged gas; Example: the sun or any other gas; Example: the sun or any other starstar

Gas Liquid Solid

low density high density high density

fills container completely

does not expand to fill

container - has definite volume

rigidly retains its volume

assumes shape of container

assumes shape of container

retains own shape

The Particulate Nature of Matter

All matter is made up of atoms

• Elements consist of atoms of the same type– H, He, Cs, Ru, Fe, O

• Compounds are formed when atoms chemically bond to one another in a specific way– CO, H2O, NaBr, C6H12O6

Properties of Matter

• Physical vs. Chemical Properties–physical property - characteristic

of a substance that can be observed without changing the substance’s identity

–chemical property - characteristic of a substance that can only be observed if the identity of the substance is changed

Physical Physical PropertiesProperties

What are some What are some physical properties?physical properties?

• colorcolor• melting and boiling melting and boiling

pointpoint• odorodor

ChemicalChemicalPropertiesProperties

What are some What are some chemical properties?chemical properties?

• FlammabilityFlammability• Reactivity with waterReactivity with water• If it tarnishesIf it tarnishes

Physical vs. Chemical Properties

• Examples:– melting point

– flammable

– density

– magnetic

– tarnishes in air

physical

chemical

physical

physical

chemical

Changes of Matter

• Physical vs. Chemical Changes–physical change - change in one or

more physical properties, but does not affect the composition of a substance

–chemical change - change in the composition of a substance, in which a substance becomes a new substance (aka, a chemical reaction)

Physical ChangesPhysical ChangesSome Some physical changes physical changes

would bewould be• boiling of a liquidboiling of a liquid• melting of a solidmelting of a solid• dissolving a solid in a dissolving a solid in a

liquid to give a liquid to give a homogeneous homogeneous mixture — a mixture — a SOLUTION.SOLUTION.

Chemical ChangesChemical ChangesSome Some chemical chemical

changes changes would bewould be• Hydrogen and oxygen Hydrogen and oxygen

combining to form combining to form waterwater

• Silver tarnishingSilver tarnishing• Baking a cakeBaking a cake• Any chemical Any chemical

reaction!reaction!

Sure Signs of a Sure Signs of a Chemical ChangeChemical Change

• HeatHeat• LightLight• Gas Produced Gas Produced

(not from (not from boiling!)boiling!)

• Precipitate – a Precipitate – a solid formed by solid formed by mixing two mixing two liquids togetherliquids together

http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA0/MOVIES/S1047.MOV

Physical vs. Chemical Changes

• Examples:– rusting iron

– dissolving in water

– burning a log

– melting ice

– grinding spices

chemicalphysical

chemical

physical

physical

Classifying Matter

–pure substances (elements and compounds); always have the same composition

–mixtures (heterogeneous and homogeneous); composition varies; made up of 2 or more pure substances

How do you know what type of matter it is?

–Pure substances»elements cannot be broken down into anything smaller than the representative atoms

»compounds can be chemically separated (decomposed), using chemical reactions

How do you know what type of matter it is?

–Mixtures: can be separated physically

»homogeneous = “same throughout”; no visibly different parts; uniform; a solution

»heterogeneous = contains regions with different properties; visibly different areas; doesn’t mix (not uniform)

Types of Mixtures

• Variable combination of 2 or more pure substances.

Heterogeneous –visibly separate parts

Homogeneous – Same throughout

Mixture Separation Techniques

• filtration - separation of solid from a liquid using filter paper–only one for heterogeneous

mixtures–parts already have to be in

different states for filtration to work

• distillation - depends on different boiling points of the substances in a solution

Mixture Separation Techniques

• chromatography - separates parts of a solution using their different levels of attraction for a stationary substance

• crystallization - boils off liquid to leave crystallized (solidified) substance that had been dissolved in the liquid

Matter Flowchart

MATTER

Can it be physically separated?

yes no

Can it be chemically decomposed?

noyesIs the composition uniform?

noyes

Matter Flowchart

MATTER

Can it be physically separated?

Homogeneous Mixture

(solution)

Heterogeneous Mixture Compound

MIXTURE PURE SUBSTANCE

yes no

Can it be chemically decomposed?

noyesIs the composition uniform?

noyes

Element