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Chapter 3 Atoms and Elements

3.1Classification of Matter

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Matter

Matter is the “stuff” that makes up all things.

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A pure substance is classified as

• matter with a specific composition.

• an element when composed of one type of atom.

• a compound when composed of two or more elements combined in a definite ratio.

Pure Substances

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Elements

Elements are • pure substances that

contains atoms of only one type.

Copper, Cu

Lead, Pb

Aluminum, Al

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Compounds

Compounds

• contain two or more elements in a definite ratio.

Salt (NaCl)

Table sugar (C12H22O11)

Water (H2O)

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Elements in a Compound

“Table salt” is a compound that contains the elements sodium and chlorine.

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Mixtures

A mixture is a type of matter that consists of

• two or more substances that are physically mixed, not chemically combined.

• two or more substances in different proportions.

• substances that can be separated by physical methods.

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Physical Separation of a Mixture

Example:

Pasta and water are separated with a strainer.

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Homogeneous Mixtures

In a homogeneous mixture,

• the composition is uniform

throughout.• the different parts of the

mixture are not visible.

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Heterogeneous Mixtures

In a heterogeneous mixture, • the composition of

substances is not uniform.• the composition varies from

one part of the mixture to another.

• the different parts of the mixture are visible.

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Classification of Matter

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Identify each of the following as a pure substance or a mixture.

A. pasta and tomato sauce

B. aluminum foil

C. helium

D. air

Learning Check

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Identify each of the following as a pure substance or a mixture.

A. pasta and tomato saucemixture

B. aluminum foil pure substance

C. helium pure substance

D. air mixture

Solution

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Identify each of the following as a homogeneous orheterogeneous mixture:

A. hot fudge sundae

B. air

C. sugar water

D. peach pie

Learning Check

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Identify each of the following as a homogeneous orheterogeneous mixture:

A. hot fudge sundae heterogeneous mixture

B. air homogeneous mixture

C. sugar water homogeneous mixture

D. peach pie heterogeneous mixture

Solution