2.1 classifying matter a. pure substance – the matter that always has exactly the same...

2.1 Classifying Matter

A. Pure substance – the matter that always has exactly the same composition.

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

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

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

I. Classifying Matter


B. element - a substance that cannot be broken down into simpler substances.

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

a. Atom- the smallest particle of an element

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


2. Examples of Elements

a. Some elements are solids at room temperature.

1) Aluminum in soft drink cans

2) Carbon in pencil lead

b. The elements are gases at room temperature

1) oxygen and nitrogen in the air you breathe.

c. Two elements are liquids at room temperature

1) bromine and mercury.


3. Symbols for Elements

a. 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.

1) C represents carbon.

2) Al represents aluminum.

3) Au represents gold. (The Latin name for gold is aurum.)


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.

Elements

Aluminum Carbon Gold Iodine


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

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

a. Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid.

b. Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other substances to burn.

C. compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances.


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

a. Mixtures can retain some of the properties of their individual substances.

b. The properties of a mixture are less constant than the properties of a substance.

D. Mixtures


2. Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.

a. heterogeneous mixture, the parts of the mixture are noticeably different from one another.

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


E. Solutions, Suspensions, and Colloids1. Based on the size of its largest particles, a mixture can be

classified as a solution, a suspension, or a colloid.

a. Solution- when substances dissolve and form a homogenous mixture

1) Windshield wiper fluid


b. Suspension- a heterogeneous mixture that separates into layer over time

1) Muddy water collected from a pond


c. Colloid- contains some particles that are intermediate in size between the small particles of a solution and the larger particles in a suspension.

1) Do not separate into layers

2) You cannot use a filter to separate the parts


Assessment Questions

1. Which of these substances is a compound? a. copper

b. water

c. oxygen

d. Carbon

ANS: B



2. Which of these groups of letters could be used as a symbol for an element? a. HF

b. Cm

c. Car

d. Fe

ANS: B & D



3. Which of the following statements does not apply to a compound? a. It is made of two or more elements.

b. It has components that are joined in fixed proportions.

c. It can be separated into components by physical methods.

d. It can be broken down into elements or other compounds.

ANS: C



4. How does a compound differ from a mixture? a. A compound cannot be broken down into simpler

substances.

b. Compounds can be separated by physical processes and mixtures cannot.

c. The composition of a mixture cannot vary.

d. A compound is made of two or more elements in fixed proportion.

ANS: D



5. Which of these materials is a heterogeneous mixture? a. air

b. seawater

c. sand

d. Steel

ANS: C



6. Which of the following can be separated with a filter? a. colloids

b. compounds

c. solutions

d. Suspensions

ANS: D

2.1 classifying matter a. pure substance – the matter that always has exactly the same...

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