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Chapter 2 Chapter 2 Properties of MatterProperties of Matter
A A pure substancepure substance isis matter that always has matter that always has exactly the same composition. exactly the same composition.
• Table salt and table sugar are two Table salt and table sugar are two examples of pure substances. examples of pure substances.
• Substances can be classified into two categories—Substances can be classified into two categories—elements and compounds.elements and compounds.
Every sample of a given substance has the same Every sample of a given substance has the same properties because a substance has a fixed, properties because a substance has a fixed, uniform composition.uniform composition.
Pure Substances
An An elementelement is a substance is a substance that cannot be broken down that cannot be broken down into simpler substances.into simpler substances.
- No two elements - No two elements contain the same type contain the same type of atom.of atom.
Elements
Examples of ElementsExamples of Elements• Some elements are solids at room temperature. Some elements are solids at room temperature.
• The elements oxygen and nitrogen are the main gases in The elements oxygen and nitrogen are the main gases in the air you breathe. the air you breathe.
• Two elements that are liquids at room temperature – Two elements that are liquids at room temperature – bromine and mercury.bromine and mercury.
Elements
Symbols for ElementsSymbols for Elements
Chemists use symbols of one or two letters to represent Chemists use symbols of one or two letters to represent elements. The first letter is always capitalized. If there is elements. The first letter is always capitalized. If there is a second letter, it is not capitalized.a second letter, it is not capitalized.
• C represents carbon.C represents carbon.• Al represents aluminum.Al represents aluminum.• Au represents gold. (The Latin name for gold is Au represents gold. (The Latin name for gold is aurum.aurum.))
Elements
Symbols for ElementsSymbols for Elements
Symbols allow scientists who speak different Symbols allow scientists who speak different languages to communicate without confusion. languages to communicate without confusion.
- - For example, nitrogen is For example, nitrogen is azote azote in France, in France, stickstoff stickstoff in Germany, and in Germany, and nitrógeno nitrógeno in Mexico. But all in Mexico. But all scientists use N as the symbol for the element nitrogen.scientists use N as the symbol for the element nitrogen.
Elements
Aluminum, carbon, and gold are elements that Aluminum, carbon, and gold are elements that you can see in common objects, such as cans, you can see in common objects, such as cans, pencils, and rings. Mixtures containing iodine are pencils, and rings. Mixtures containing iodine are used to prevent and treat infections. used to prevent and treat infections.
Elements
Aluminum Carbon Gold Iodine
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.
Compounds
A A compoundcompound is a substance that is made from two or is a substance that is made from two or more simpler substances and can be broken down into more simpler substances and can be broken down into those simpler substances.those simpler substances.
The properties of a compound differ from those of The properties of a compound differ from those of the substances from which it is made. the substances from which it is made.
- Water is composed of the elements hydrogen and - Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid.temperature, but water is a liquid.
- Hydrogen can fuel a fire, and oxygen can keep a fire - Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other burning, but water does not burn or help other substances to burn.substances to burn.
Compounds
Silicon dioxide is a compound found in most light-colored grains of Silicon dioxide is a compound found in most light-colored grains of sand and in crystals of quartz. sand and in crystals of quartz.
It is a colorless, transparent solid. Yet, silicon dioxide is made from It is a colorless, transparent solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a gray solid (silicon). a colorless gas (oxygen) and a gray solid (silicon).
In silicon dioxide, there are always two oxygen atoms for each In silicon dioxide, there are always two oxygen atoms for each silicon atom. silicon atom.
Compounds
Silicon Oxygen Silicon dioxide
If you make salsa, a recipe can guide you. You can If you make salsa, a recipe can guide you. You can use exactly the amounts in the recipe, or you can use exactly the amounts in the recipe, or you can adjust the ingredients to your own taste. Salsa is a adjust the ingredients to your own taste. Salsa is a mixture. Each batch may be slightly different.mixture. Each batch may be slightly different.
Mixtures
The properties of a mixture can vary because the The properties of a mixture can vary because the composition of a mixture is not fixed.composition of a mixture is not fixed.• Mixtures can retain some of the properties of their Mixtures can retain some of the properties of their
individual substances. individual substances. • The properties of a mixture are less constant than the The properties of a mixture are less constant than the
properties of a substance.properties of a substance.
Mixtures
Mixtures can be classified by how well the parts of the mixture Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.are distributed throughout the mixture.
Heterogeneous MixturesHeterogeneous Mixtures
In a In a heterogeneous mixture, heterogeneous mixture, the parts of the the parts of the mixture are noticeably different from one another.mixture are noticeably different from one another.
Homogeneous MixturesHomogeneous Mixtures
In a In a homogeneous mixture, homogeneous mixture, the substances are so the substances are so evenly distributed that it is difficult to distinguish one evenly distributed that it is difficult to distinguish one substance in the mixture from another.substance in the mixture from another.
Mixtures
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The sand is a heterogeneous The sand is a heterogeneous mixture of different kinds mixture of different kinds of grains. The spoon is of grains. The spoon is stainless steel, a stainless steel, a homogeneous mixture of homogeneous mixture of iron, chromium, and nickel.iron, chromium, and nickel.
Mixtures
Solutions Solutions
When substances dissolve and form a When substances dissolve and form a homogeneous mixture, the mixture that forms is homogeneous mixture, the mixture that forms is called a called a solutionsolution..
Suspensions Suspensions
A A suspensionsuspension is a heterogeneousis a heterogeneous
mixture that separates into layers mixture that separates into layers
over time.over time.
Solutions, Suspensions, and Colloids
Colloids Colloids
A A colloidcolloid contains some particles that are contains some particles that are intermediate in size between the small particles in intermediate in size between the small particles in a solution and the larger particles in a suspension. a solution and the larger particles in a suspension.
• Like solutions, colloids do not separate into layers. Like solutions, colloids do not separate into layers. • You cannot use a filter to separate the parts of a You cannot use a filter to separate the parts of a
colloid.colloid.
Solutions, Suspensions, and Colloids
These liquids represent three categories of These liquids represent three categories of mixtures. mixtures.
• Windshield wiper fluid is a solution. Windshield wiper fluid is a solution. • Muddy water collected from a swamp is a Muddy water collected from a swamp is a
suspension. suspension. • Milk is a colloid. Milk is a colloid.
Solutions, Suspensions, and Colloids
Assessment Questions
1.1. Which of these substances is a compound? Which of these substances is a compound? a.a. coppercopper
b.b. waterwater
c.c. oxygenoxygen
d.d. carboncarbon
Assessment Questions
1.1. Which of these substances is a compound? Which of these substances is a compound? a.a. coppercopper
b.b. waterwater
c.c. oxygenoxygen
d.d. carboncarbon
ANS:ANS: BB
Assessment Questions
2.2. Which of these groups of letters could be Which of these groups of letters could be used as a symbol for an element? used as a symbol for an element?
a.a. HFHF
b.b. CmCm
c.c. CarCar
d.d. fefe
Assessment Questions
2.2. Which of these groups of letters could be Which of these groups of letters could be used as a symbol for an element? used as a symbol for an element?
a.a. HFHF
b.b. CmCm
c.c. CarCar
d.d. fefe
ANS:ANS: B B
Assessment Questions
3.3. Which of the following statements does not Which of the following statements does not apply to a compound? apply to a compound?
a.a. It is made of two or more elements.It is made of two or more elements.
b.b. It has components that are joined in fixed It has components that are joined in fixed proportions.proportions.
c.c. It can be separated into components by physical It can be separated into components by physical methods.methods.
d.d. It can be broken down into elements or other It can be broken down into elements or other compounds.compounds.
Assessment Questions
3.3. Which of the following statements does not Which of the following statements does not apply to a compound? apply to a compound?
a.a. It is made of two or more elements.It is made of two or more elements.
b.b. It has components that are joined in fixed It has components that are joined in fixed proportions.proportions.
c.c. It can be separated into components by physical It can be separated into components by physical methods.methods.
d.d. It can be broken down into elements or other It can be broken down into elements or other compounds.compounds.
ANS:ANS: CC
Assessment Questions
4.4. How does a compound differ from a How does a compound differ from a mixture? mixture?
a.a. A compound cannot be broken down into A compound cannot be broken down into simpler substances.simpler substances.
b.b. Compounds can be separated by physical Compounds can be separated by physical processes and mixtures cannot.processes and mixtures cannot.
c.c. The composition of a mixture cannot vary.The composition of a mixture cannot vary.
d.d. A compound is made of two or more elements in A compound is made of two or more elements in fixed proportion.fixed proportion.
Assessment Questions
4.4. How does a compound differ from a How does a compound differ from a mixture? mixture?
a.a. A compound cannot be broken down into A compound cannot be broken down into simpler substances.simpler substances.
b.b. Compounds can be separated by physical Compounds can be separated by physical processes and mixtures cannot.processes and mixtures cannot.
c.c. The composition of a mixture cannot vary.The composition of a mixture cannot vary.
d.d. A compound is made of two or more elements in A compound is made of two or more elements in fixed proportion.fixed proportion.
ANS:ANS: D D
Assessment Questions
5.5. Which of these materials is a Which of these materials is a heterogeneous mixture? heterogeneous mixture?
a.a. airair
b.b. seawaterseawater
c.c. sandsand
d.d. steelsteel
Assessment Questions
5.5. Which of these materials is a Which of these materials is a heterogeneous mixture? heterogeneous mixture?
a.a. airair
b.b. seawaterseawater
c.c. sandsand
d.d. steelsteel
ANS:ANS: C C
Assessment Questions
6.6. Which of the following can be separated Which of the following can be separated with a filter? with a filter?
a.a. colloidscolloids
b.b. compoundscompounds
c.c. solutionssolutions
d.d. suspensionssuspensions
Assessment Questions
6.6. Which of the following can be separated Which of the following can be separated with a filter? with a filter?
a.a. colloidscolloids
b.b. compoundscompounds
c.c. solutionssolutions
d.d. suspensionssuspensions
ANS:ANS: D D
