Chapter 2 Properties of Matter

Pure Substances A pure substance is matter that always has exactly the same composition. Table salt and table sugar are two examples of pure substances. Substances can be classified into two categories—elements and compounds. Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.

Elements An element is a substance that cannot be broken down into simpler substances. - No two elements contain the same type of atom.

Elements Examples of Elements Some elements are solids at room temperature. The elements oxygen and nitrogen are the main gases in the air you breathe. Two elements that are liquids at room temperature – bromine and mercury.

Elements Symbols for Elements Chemists use symbols of one or two letters to represent elements. The first letter is always capitalized. If there is a second letter, it is not capitalized. C represents carbon. Al represents aluminum. Au represents gold. (The Latin name for gold is aurum.)

Elements Symbols for Elements Symbols allow scientists who speak different languages to communicate without confusion. - For example, nitrogen is azote in France, stickstoff in Germany, and nitrógeno in Mexico. But all scientists use N as the symbol for the element nitrogen.

Elements Aluminum, carbon, and gold are elements that you can see in common objects, such as cans, pencils, and rings. Mixtures containing iodine are used to prevent and treat infections. Gold Aluminum Carbon Iodine

Compounds A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances. A compound always contains two or more elements joined in a fixed proportion.

Compounds The properties of a compound differ from those of the substances from which it is made. - Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid. - Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other substances to burn.

Compounds Silicon dioxide is a compound found in most light-colored grains of sand and in crystals of quartz. It is a colorless, transparent solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a gray solid (silicon). In silicon dioxide, there are always two oxygen atoms for each silicon atom. Oxygen Silicon dioxide Silicon

Mixtures If you make salsa, a recipe can guide you. You can use exactly the amounts in the recipe, or you can adjust the ingredients to your own taste. Salsa is a mixture. Each batch may be slightly different.

Mixtures The properties of a mixture can vary because the composition of a mixture is not fixed. Mixtures can retain some of the properties of their individual substances. The properties of a mixture are less constant than the properties of a substance.

Mixtures Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture. Heterogeneous Mixtures In a heterogeneous mixture, the parts of the mixture are noticeably different from one another. Homogeneous Mixtures In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.

Mixtures The sand is a heterogeneous mixture of different kinds of grains. The spoon is stainless steel, a homogeneous mixture of iron, chromium, and nickel.

Solutions, Suspensions, and Colloids When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution. Suspensions A suspension is a heterogeneous mixture that separates into layers over time.

Solutions, Suspensions, and Colloids A colloid contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension. Like solutions, colloids do not separate into layers. You cannot use a filter to separate the parts of a colloid.

Solutions, Suspensions, and Colloids These liquids represent three categories of mixtures. Windshield wiper fluid is a solution. Muddy water collected from a swamp is a suspension. Milk is a colloid.

Which of these substances is a compound? Assessment Questions Which of these substances is a compound? copper water oxygen carbon

Which of these substances is a compound? Assessment Questions Which of these substances is a compound? copper water oxygen carbon ANS: B

Assessment Questions Which of these groups of letters could be used as a symbol for an element? HF Cm Car fe

Assessment Questions Which of these groups of letters could be used as a symbol for an element? HF Cm Car fe ANS: B

Which of the following statements does not apply to a compound? Assessment Questions Which of the following statements does not apply to a compound? It is made of two or more elements. It has components that are joined in fixed proportions. It can be separated into components by physical methods. It can be broken down into elements or other compounds.

Which of the following statements does not apply to a compound? Assessment Questions Which of the following statements does not apply to a compound? It is made of two or more elements. It has components that are joined in fixed proportions. It can be separated into components by physical methods. It can be broken down into elements or other compounds. ANS: C

How does a compound differ from a mixture? Assessment Questions How does a compound differ from a mixture? A compound cannot be broken down into simpler substances. Compounds can be separated by physical processes and mixtures cannot. The composition of a mixture cannot vary. A compound is made of two or more elements in fixed proportion.

How does a compound differ from a mixture? Assessment Questions How does a compound differ from a mixture? A compound cannot be broken down into simpler substances. Compounds can be separated by physical processes and mixtures cannot. The composition of a mixture cannot vary. A compound is made of two or more elements in fixed proportion. ANS: D

Which of these materials is a heterogeneous mixture? Assessment Questions Which of these materials is a heterogeneous mixture? air seawater sand steel

Which of these materials is a heterogeneous mixture? Assessment Questions Which of these materials is a heterogeneous mixture? air seawater sand steel ANS: C

Which of the following can be separated with a filter? Assessment Questions Which of the following can be separated with a filter? colloids compounds solutions suspensions

Which of the following can be separated with a filter? Assessment Questions Which of the following can be separated with a filter? colloids compounds solutions suspensions ANS: D