A mixture is a combination of two or more substances in which the basic identity of each substance...

• A mixture is a combination of two or more substances in which the basic identity of eachsubstance is not changed.

• Unlike pure substances, mixtures do not have specific compositions.

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Chemistry and Matter: Basic ConceptsChemistry and Matter: Basic Concepts Chemistry and Matter: Basic ConceptsChemistry and Matter: Basic Concepts

Pure substance or a mixture?

• A physical change is a change in matter that does not involve a change in the chemical identity of individual substances.

• Examples of physical changes include:

• boiling,

• freezing,

• melting,

• evaporating,

• dissolving,

• and crystallizing.

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• Physical properties are characteristics that a sample of matter exhibits without any change in its identity.

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• Examples of the physical properties of a chunk of matter include its:• solubility,• melting point,• boiling point,• color,• density,• electrical conductivity,• and physical state (solid, liquid, or gas).

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• Homogeneous mixtures are the same throughout.

• Another name for a homogeneous mixture is solution.

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• Some solutions are gases. Air, for example, is a homogeneous mixture of several gases.

• Some solutions are solid.

• Liquid solutions do not have to be liquid or contain water.

• When you dissolve sugar in water, sugar is the solute—the substance being dissolved.

• The substance that dissolves the solute, in this case water, is the solvent.

• When the solvent is water, the solution is called an aqueous solution.

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• Many of the solutions you encounter are aqueous solutions, for example, soda, tea, contact-lens cleaner, and other clear cleaning liquids.

• In addition, most of the processes of life occur in aqueous solutions.

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Two Types of Substances

• One type of pure substance can be broken down into simpler substances. This type of substance is called a compound.

• Another type of substance cannot be broken down into simpler substances. Such a substance is called an element.

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• All the substances of the universe are either elements, compounds formed from elements, or mixtures of elements and compounds.

Two Types of Substances

• Of the known elements, only about 90 occur naturally on Earth. The remainder are synthesized, usually in barely detectable amounts, in high-energy nuclear experiments. • Less than half of the 90 naturally occurring elements are abundant enough to play a significant role in the chemistry of everyday stuff.

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Compounds Are More Than One Element

• A more complete definition is that a compound is a chemical combination of two or more different elements joined together in a fixed proportion with a unique set of chemical and physical properties.

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• More than 10 million compounds are known and the number keeps growing.

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• Some new compounds are discovered and isolated from natural chemical sources such as plants and colonies of bacteria and are synthesized in laboratories for many different uses.


• The properties of the compound are different from the properties of the elements that compose the compound.

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silver + bromine = silver bromide


• A formula is a combination of the chemical symbols that show what elements make up a compound and the number of atoms of each element.

Compound Formula

Caffeine C8H10N4O2

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• Formulas provide a shorthand way of describing a submicroscopic view of a compound.

• You probably already use formulas like H2O and CO2 as a way of talking about water and carbon dioxide.

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Organizing the Elements

• The periodic table organizes elements in a way that provides a wealth of chemical information—much more than is evident to you now. It shows the chemical symbols for the elements.

• Their symbols usually correspond to their names in Latin.

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Periodic Table of the Elements

• MODERN PERIODIC TABLE• Arranged in order of increasing atomic number• Rows are called periods• Columns are called groups or families • Periodic Law – elements arranged in increasing

atomic number have a periodic pattern in their physical and chemical properties.

• Elements with similar properties are in the same group.

Basic Assessment QuestionsBasic Assessment Questions

Question 1

Identify each of the following as either a compound or a mixture.

A. sand

B. water

C. juice

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Answers

A. sand

B. water

C. juice

mixture

compound

mixture

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Classify each of the following as an intensive or extensive physical property.

Question 2

A. density

B. mass

C. color

D. melting pointE. volume

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Answers

A. density

B. mass

C. color

D. melting point

intensive property

extensive property

intensive property

intensive property

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E. volume extensive property

A mixture is a combination of two or more substances in which the basic identity of each substance...

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