Learning Objective• Classify matter as a pure substance or

mixture by investigating its properties

Classification of Matter

• Pure substances have a defined chemical composition

Ex)

• Mixtures are formed from physically mixing two or more pure substances

Ex)

Classifications of Matter

Pure Substanc

e

Defined Composit

ion

Aluminum

Al

Oxygen O2

Water H2O

Sugar C6H12O6

Mixture Composition

Trail mix varies

Sugar water

varies

Air varies

• Element – pure substance consisting of only one type of atom

• All known elements are listed in the periodic table

• Some elements always appear as groups of two– Diatomic elements –– H2, N2, O2, F2, Cl2, Br2, I2

• Some elements exist in multiple forms– Carbon exists as graphite or diamond

Types of Pure Substances

• Compound – two or more atoms of different elements chemically combined in a fixed ratio

• Molecule – group of covalently bonded atoms with a fixed composition

• Compositions of pure substances are described by formulas– Subscripts in formulas represent how many

atoms of that element are present in the compound or molecule• Subscripts are written after the element they apply to

– C6H12O6 has six carbon atoms, 12 hydrogen atoms, and six oxygen atoms

• Subscripts of 1 are implied rather than written– H2O has two hydrogen atoms and one oxygen atom

Types of Pure Substances

• Compounds have different properties from the elements that make them upEx)

Properties of Compounds

Pure Substan

ce

Formula

Properties Image Image

Credit

Sodium Na highly reactive metal

By Dnn87 at en.wikipedia (Transferred

from en.wikipedia) [CC–BY–SA–

3.0]

Chlorine

Cl2 highly toxic

green gas

By W. Oelen (http://woelen.homescience.net/science/in

dex.html) [CC–BY–SA–

3.0]

Sodium chloride

NaCl stable white

crystal eaten

everyday

By Dubravko Sorić SoraZG on Flickr [CC–

BY–2.0]

• Law of definite proportions – a chemical compound will always contain the same ratio of elements

• Law of multiple proportions – if multiple compounds can form from the combination of elements, the elements will always combine in small, defined whole number ratios– Ratio of the elements determines the chemical

identity of the compoundEx)

Laws Governing Compounds

Common Name

Elements Present

Formula of Compound

Ratio of Elements

Water Hydrogen & Oxygen

H2O 2:1

Hydrogen Peroxide

Hydrogen & Oxygen

H2O2 2:2

• Heterogeneous mixture – a mixture that is not uniform throughout– Different properties in

different parts of the specimen

• Homogeneous mixture – a mixture that is uniform throughout– Same properties in

different parts of the specimen

– Also called a solution

Types of Mixtures

Heterogeneous MixtureBy Victor Blacus (Victor Blacus) [GFDL]

Solution

• Mixtures do not have defined ratios

• Properties of mixtures are generally a blend of the properties of the substances they are made from

Properties of Mixtures

Chocolate chip cookies

By Rdsmith4 (Own work) [CC–BY–SA–2.5]

• Separation of mixtures is a physical process– Based on

differences in the properties of the substances

• Separation of compounds is a chemical process– A chemical

reaction must occur to break a compound into elements• Elements cannot be

separated any further

Separating Mixtures and Pure Substances

Types of Physical

Separations

Reason for Separation

Filtration Particle Size

Distillation Difference in boiling points

Chromatography

Differences in attraction to various liquids or solids

Classification of Matter

Matter

Uniform Throughout

Physically Combined

Homogeneous MixtureEx) salt water

Chemically Combined

CompoundEx) H2O

Uncombined

ElementEx) Al

Not Uniform Throughout

Heterogeneous Mixture

Ex) oil & water