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SubstancesSubstances

A pure substance is an element or a compound.

Substances have the same characteristicsthroughout meaning that all samples have thesame characteristics.

An element is a substance composed of only onekind of atom.

Elements can not be broken down into a simplersubstance by ordinary chemical means.

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Elements and CompoundsElements and Compounds

Examples of elements:

oxygen, carbon, nitrogen

Compounds are homogeneous substancesformed by the chemical bonding of two ormore different kinds of atoms resulting

from achemical reaction.

Compounds have properties uniquelydifferent from the elements making it up.

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CompoundsCompounds

Examples of compounds:

water, carbon dioxide, sodium chloride

The Law of Definite Proportions states themass of the constituent elements alwaysremains the same.

In every 100. g sample of NaCl, 39.3 g is

sodium and 60.7 g of chlorine.

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CompoundsCompounds and Mixtures and Mixtures

When a compound is formed, evidence of achemical reaction is usually obvious.

Light is given off or heat is either absorbed or liberated.

Mixtures are physical combinations of two or

more substances.

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MixturesMixtures

In a mixture, the components can be presentin any proportion.

NaCl(aq) – a salt water solution can existin any proportion.

When a mixture is formed, there is noevidence of a chemical reaction taking place.

In a mixture, the components do not lose theiridentity.

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MixturesMixtures

Mixtures can be either homogeneous orheterogeneous.

Mixtures having uniform characteristics

are homogeneous.

Mixtures having varying characteristics throughout the sample are heterogeneous.

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ClassificationClassification of Matter of Matter

Matter

Pure Substance

Mixture

Element

Compound

Homogeneous

Heterogeneous

Matter

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Physical Physical PropertiesProperties

Characteristics that can be observed withoutproducing a new substance.

ExamplesExamples

color densityodormelting point

volume boiling point

compressibility mass

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Chemical Chemical PropertiesProperties

Characteristics that describe how asubstance reacts with another substance to form a new substance.

2H2(g) + O2(g) 2H2O(l)

The reactants hydrogen and oxygen havemuch different characteristics than theproduct water.

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PhysicalPhysical Changes Changes

No new substances are formed as a result of

a physical change.

In a physical change, one or more physicalproperties are changed.

Changes of state or phase such ascondensation or vaporization and changes

insize by tearing, breaking, grinding areexamples of physical changes.

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ChemicalChemical Changes Changes

A chemical change results in the formation of

one or more new substances.

The new substances differ in chemicalproperties and composition from the originalsubstance.

Examples of Chemical Changes

rusting of iron

burning of paper

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ChemicalChemical Changes Changes

When the following are not associated with achange of phase (state), they represent achemical change.

formation of a gas (bubbles)

formation of a solid (precipitate)

absorbing (endothermic) or giving (exothermic) off heat

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PropertiesProperties

Properties are characteristics that used todescribe substances.

Properties can be either extensive orintensive.

Extensive properties depend on the amountof substance present.

Examples are weight, mass, volume, and length.

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PropertiesProperties

Intensive properties are independent of theamount of substance present.

Examples are density, temperature, and boiling point.

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Law of Definite ProportionsLaw of Definite Proportions

Once a given compound is formed, itschemical composition is always constant.

2C(s) + O2(g) → 2CO(g)

The mass ratio is: C:O 12 g:16 g

The atom ratio is: C:O 1 C:1 O

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Law of Law of MultipleMultiple Proportions Proportions

Two elements combining with each other may

join in varying ratios to form differentcompounds (compare to the product

formedin previous slide).

C(s) + O2(g) → CO2(g)

The mass ratio is: C:O 12 g:32 g

The atom ratio is: C:O 1 C:2 O

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Dalton’s Dalton’s AtomicAtomic Theory Theory

All matter is composed of atoms and an atom

is the smallest particle of an element that takes

part in a chemical reaction.

All atoms of an element are alike.

Compounds are combinations of atoms of one

or more elements. The relative number ofatoms for each element is always the same.

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Dalton’s Dalton’s AtomicAtomic Theory Theory

Atoms can not be created or destroyed in achemical reaction.

Atoms can only change how they combine with

each other.