Chapter 3Chapter 3

Matter—Properties and Matter—Properties and ChangesChanges

Classifying MatterClassifying Matter

The word The word compositioncomposition comes comes from a Latin word meaning “a from a Latin word meaning “a putting together,” or the putting together,” or the combining of parts into a combining of parts into a whole. whole.

Based on their compositions, Based on their compositions, materials can be divided into materials can be divided into pure substances and mixtures. pure substances and mixtures.

Pure SubstancesPure Substances Matter that always has exactly the same Matter that always has exactly the same

composition is classified as a composition is classified as a pure pure substancesubstance, or simply a substance. , or simply a substance.

Table salt and table sugar are two Table salt and table sugar are two examples of pure substances. examples of pure substances.

Every pinch of salt tastes equally salty. Every pinch of salt tastes equally salty. Every spoonful of sugar tastes equally Every spoonful of sugar tastes equally sweet.   sweet.  

Every sample of a given substance has Every sample of a given substance has the same properties because a substance the same properties because a substance has a fixed, uniform composition. has a fixed, uniform composition.

Substances can be classified into two Substances can be classified into two categories—elements and compounds. categories—elements and compounds.

Examples of Physical Examples of Physical PropertiesProperties

A A physical propertyphysical property is any is any characteristic of a material that can characteristic of a material that can be observed or measured without be observed or measured without changing the composition of the changing the composition of the substances in the material. substances in the material.    

Density, color, odor, taste, Density, color, odor, taste, hardness, melting point, and hardness, melting point, and boiling point are examples boiling point are examples of physical properties.of physical properties.

Extensive and Intensive Extensive and Intensive PropertiesProperties

Extensive propertiesExtensive properties are are properties that are dependent upon properties that are dependent upon the amount of substance present. the amount of substance present. For example, mass, length, volume.For example, mass, length, volume.

Intensive propertiesIntensive properties are properties are properties that are not dependent that are not dependent (independent) of the amount of (independent) of the amount of substance present. For example, substance present. For example, density.density.

Using Properties to Using Properties to Identify MaterialsIdentify Materials

The steps used to identify a The steps used to identify a material are similar to the material are similar to the steps used to test for purity. steps used to test for purity.

1.1. The first step is to decide which The first step is to decide which properties to test. properties to test.

2.2. The second step is to do tests on The second step is to do tests on a sample of the unknown. a sample of the unknown.

3.3. The final step is to compare the The final step is to compare the results with the data reported results with the data reported for known materials. for known materials.

Chemical PropertiesChemical Properties

A A chemical propertychemical property is any is any ability to produce a change in ability to produce a change in the composition of matter. the composition of matter.    

Chemical properties can be Chemical properties can be observed only when the observed only when the substances in a sample of substances in a sample of matter are changing into matter are changing into different substancesdifferent substances..

Flammability and reactivity are Flammability and reactivity are two examples of chemical two examples of chemical properties. properties.

States of MatterStates of Matter

Materials can be classified as Materials can be classified as solids, liquids or gases based on solids, liquids or gases based on whether their shapes and volumes whether their shapes and volumes are definite or variable.are definite or variable.

Shape and volume are clues to Shape and volume are clues to how the particles in the material how the particles in the material are arranged.are arranged.

SolidsSolids SolidsSolids are the state of matter in which are the state of matter in which

the material has a definite shape and the material has a definite shape and definite volume.definite volume.

Definite means that the volume and Definite means that the volume and shape of the object does not change as shape of the object does not change as you move it.you move it.

But that does not mean that the shape But that does not mean that the shape and volume will never change.and volume will never change.

In solids, the particles are packed In solids, the particles are packed close together in a regular pattern close together in a regular pattern and very orderly arranged on the and very orderly arranged on the atomic level.atomic level.

LiquidsLiquids Liquid Liquid is the state of matter that is the state of matter that

has a definite volume but no has a definite volume but no definite shape.definite shape.

Liquids take the shape of their Liquids take the shape of their container and can be poured from container and can be poured from one container to another.one container to another.

The atoms in liquids are still The atoms in liquids are still closely packed but are less orderly closely packed but are less orderly arranged.arranged.

GasesGases GasesGases are the state of matter that has are the state of matter that has

no definite shape and no definite no definite shape and no definite volume.volume.

A gas takes the shape and volume of its A gas takes the shape and volume of its container.container.

Gas particles do not have an order Gas particles do not have an order arrangement in containers.arrangement in containers.

They are at random locations They are at random locations throughout the container.throughout the container.

Because of the space among particles Because of the space among particles in a gas, gases can be compressed into in a gas, gases can be compressed into metal containers.metal containers.

VaporsVapors

The words gas and vapor do not mean The words gas and vapor do not mean the same thing.the same thing.

Gas refers to a substance that is Gas refers to a substance that is naturally in the gaseous state at room naturally in the gaseous state at room temperature. For example, methane.temperature. For example, methane.

Vapor refers to the gaseous state of a Vapor refers to the gaseous state of a substance that is a solid or liquid at substance that is a solid or liquid at room temperature. For example, room temperature. For example, steam.steam.

Recognizing Physical Recognizing Physical ChangesChanges

A A physical changephysical change occurs when occurs when some of the properties of a material some of the properties of a material change, but the substances in the change, but the substances in the material remain the same. material remain the same.

For example, if you slowly heat For example, if you slowly heat butter in a pan, it changes from a butter in a pan, it changes from a solid to a liquid, but the substances solid to a liquid, but the substances in the butter do not change. in the butter do not change.

Heating, crumpling a piece of paper Heating, crumpling a piece of paper and slicing a tomato are all physical and slicing a tomato are all physical changes because they change the changes because they change the size and shape of a material, but not size and shape of a material, but not its composition. its composition.

Chemical ChangesChemical Changes

When one or more substance changes When one or more substance changes into new substances it is called a into new substances it is called a chemical changechemical change, which is commonly , which is commonly referred to as a chemical reaction.referred to as a chemical reaction.

The new substances in the reactions The new substances in the reactions have different compositions and have different compositions and different properties from the different properties from the substances present before the substances present before the reaction occurs.reaction occurs.

Recognizing Chemical ChangesRecognizing Chemical Changes The color change in a banana peel is caused The color change in a banana peel is caused

by chemical changes that are taking place in by chemical changes that are taking place in the cells of the banana. the cells of the banana.

A A chemical changechemical change occurs when a occurs when a substance reacts and forms one or more new substance reacts and forms one or more new substances. substances.

Chemical changes occur when a cake bakes Chemical changes occur when a cake bakes in an oven, leaves on trees change color, and in an oven, leaves on trees change color, and food is digested in your stomach. food is digested in your stomach.

Chemical ChangesChemical Changes How can you recognize a How can you recognize a

chemical change? You have to chemical change? You have to look for clues. For example, look for clues. For example, when food spoils, it often gives when food spoils, it often gives off an unpleasant odor. off an unpleasant odor.    

Three common types of Three common types of evidence for a chemical evidence for a chemical change are a change in color, change are a change in color, the production of a gas, and the production of a gas, and the formation of a precipitate.the formation of a precipitate.

Conservation of MassConservation of Mass

This law says that the mass before This law says that the mass before and after a chemical reaction and after a chemical reaction remains the same.remains the same.

It says that mass is neither created It says that mass is neither created or destroyed in a chemical reaction.or destroyed in a chemical reaction.

MassMassreactantsreactants=Mass=Massproductsproducts

MixturesMixtures

Mixtures tend to retain some of Mixtures tend to retain some of the properties of their individual the properties of their individual substances. substances.

The properties of a mixture can The properties of a mixture can vary because the composition of vary because the composition of a mixture is not fixed. a mixture is not fixed.

There are two types of mixtures: There are two types of mixtures: Heterogeneous and Heterogeneous and Homogeneous.Homogeneous.

Heterogeneous Heterogeneous MixturesMixtures

Heterogeneous comes from the Heterogeneous comes from the Greek words Greek words heterohetero and and genusgenus, , meaning “different” and “kind.” meaning “different” and “kind.” In a In a heterogeneous mixtureheterogeneous mixture, , the parts of the mixture are the parts of the mixture are noticeably different from one noticeably different from one another. another.

Sand is an example of a Sand is an example of a heterogeneous mixture.heterogeneous mixture.

Homogeneous Homogeneous MixturesMixtures

In a In a homogeneous mixturehomogeneous mixture, the , the substances are so evenly distributed substances are so evenly distributed that it is difficult to distinguish one that it is difficult to distinguish one substance in the mixture from another. substance in the mixture from another.

A homogeneous mixture appears to A homogeneous mixture appears to contain only one substance. contain only one substance.

A serving spoon made of stainless steel A serving spoon made of stainless steel represents a homogeneous mixture of represents a homogeneous mixture of iron, chromium, and nickel. iron, chromium, and nickel.

The water in a swimming pool is also The water in a swimming pool is also an example of a homogeneous an example of a homogeneous mixture.mixture.

Solutions, Solutions, Suspensions, and Suspensions, and

Colloids Colloids It isn't always easy to tell a homogeneous It isn't always easy to tell a homogeneous mixture from a heterogeneous mixture. mixture from a heterogeneous mixture.

You may need to observe the properties You may need to observe the properties of a mixture before you decide. of a mixture before you decide.

The size of the particles in a mixture has The size of the particles in a mixture has an effect on the properties of the an effect on the properties of the mixture.   mixture.  

Based on the size of its largest particles, Based on the size of its largest particles, a mixture can be classified as a solution, a mixture can be classified as a solution, a suspension, or a colloid. a suspension, or a colloid.

Using Properties to Using Properties to Separate MixturesSeparate Mixtures

Some properties can be used to Some properties can be used to separate mixtures. separate mixtures.

Filtration, distillation, Filtration, distillation, crystallization and crystallization and chromatography are chromatography are common separation common separation methods.methods.

Pure SubstancesPure Substances Matter that always has exactly the same Matter that always has exactly the same

composition is classified as a composition is classified as a pure pure substancesubstance, or simply a substance. , or simply a substance.

Table salt and table sugar are two Table salt and table sugar are two examples of pure substances. examples of pure substances.

Every pinch of salt tastes equally salty. Every pinch of salt tastes equally salty. Every spoonful of sugar tastes equally Every spoonful of sugar tastes equally sweet.   sweet.  

Every sample of a given substance has Every sample of a given substance has the same properties because a substance the same properties because a substance has a fixed, uniform composition. has a fixed, uniform composition.

Substances can be classified into two Substances can be classified into two categories—elements and compounds. categories—elements and compounds.

ElementsElements Although there are millions of known Although there are millions of known

substances, there are only about substances, there are only about 100 elements. 100 elements.

An An elementelement is a substance that cannot is a substance that cannot be broken down into simpler be broken down into simpler substances. substances.

An An atomatom is the smallest particle of an is the smallest particle of an element.   element.  

An element has a fixed composition An element has a fixed composition because it contains only one type of because it contains only one type of atom. atom.

No two elements contain the same type No two elements contain the same type of atom.of atom.

Examples of ElementsExamples of Elements   At room temperature (20°C, or 68°F), At room temperature (20°C, or 68°F),

most elements are solidsmost elements are solids, including , including the elements aluminum and carbon.the elements aluminum and carbon.

Some elements are gasesSome elements are gases at room at room temperature. The elements oxygen temperature. The elements oxygen and nitrogen are the main gases in and nitrogen are the main gases in the air you breathe. the air you breathe.

Only two elements are liquidsOnly two elements are liquids at room at room temperature, bromine and mercury, temperature, bromine and mercury, both of which are extremely both of which are extremely poisonous. poisonous.

Symbols for ElementsSymbols for Elements Each element has a symbol that Each element has a symbol that

consists of either one or two consists of either one or two letters. The first letter is always letters. The first letter is always capitalized. If there is a second capitalized. If there is a second letter, it is not capitalized. letter, it is not capitalized.

For most symbols it is easy to For most symbols it is easy to see what they will be, but some see what they will be, but some come from different languages, come from different languages, like Gold (Au) and silver (Ag).like Gold (Au) and silver (Ag).

Periodic TablePeriodic Table

As new elements were being As new elements were being discovered they were organized in a discovered they were organized in a periodic table.periodic table.

All elements in the world can be All elements in the world can be found on the periodic table.found on the periodic table.

CompoundsCompounds A A compoundcompound is a substance that is is a substance that is

made from two or more simpler made from two or more simpler substances and can be broken down substances and can be broken down into those simpler substances. into those simpler substances.

The simpler substances are either The simpler substances are either elements or other compounds. elements or other compounds.

The properties of a compound differ The properties of a compound differ from those of the substances from from those of the substances from which it is made. which it is made.

A compound always contains two or A compound always contains two or more elements joined in a fixed more elements joined in a fixed proportion. proportion.

Law of Definite Law of Definite ProportionsProportions

The law of definite proportions says The law of definite proportions says that regardless of the amount, a that regardless of the amount, a compound is always composed of the compound is always composed of the same elements in the same proportion same elements in the same proportion by mass.by mass.

For example, sucrose. In 20.00 g, For example, sucrose. In 20.00 g, there are always 8.44 g of carbon, 1.30 there are always 8.44 g of carbon, 1.30 g of hydrogen and 10.26 g of oxygen. g of hydrogen and 10.26 g of oxygen.

The proportion is obtained by The proportion is obtained by calculating the percent by mass.calculating the percent by mass.

Percent by MassPercent by Mass

Percent by mass of found of the Percent by mass of found of the elements in a compound by the elements in a compound by the following formula:following formula:

Percent by mass = Percent by mass = mass of elementmass of element x 100%x 100%

mass of compoundmass of compound

Law of Multiple Law of Multiple ProportionsProportions

This law states that when different This law states that when different compounds are formed by a compounds are formed by a combination of the same elements, combination of the same elements, different mass one element combine different mass one element combine with the same relative mass of the with the same relative mass of the other elements in a ratio of small other elements in a ratio of small whole numbers.whole numbers.

See page 76 in your textbook.See page 76 in your textbook.