Question

pure substances (page 39)

1. is the following sentence true or false? every sample of a pure substance has exactly the same composition and the same properties.
2. what are the two categories of pure substances?

a. b.
elements (pages 39 - 40)

1. what is an element?
2. is the following sentence true or false? the smallest particle of an element is an atom.
3. why does an element have a fixed, uniform composition?
4. circle the letter before each element that is a gas at room temperature.

a. carbon b. oxygen
c. mercury d. nitrogen
match each element to its correct symbol.
element symbol

1. aluminum a. c
2. gold b. al
3. carbon c. au

Explanation:

1. By definition, a pure substance has a definite and constant composition, and thus the same properties throughout. So the statement is true.
2. Pure substances are classified into elements and compounds.
3. An element is a pure substance that cannot be broken down into simpler substances by chemical means.
4. The smallest particle of an element that retains the chemical properties of that element is an atom, so the statement is true.
5. An element has a fixed, uniform composition because all of its atoms have the same number of protons, which defines the element's identity.
6. Oxygen and nitrogen are gases at room - temperature. Carbon is a solid and mercury is a liquid at room - temperature.

7 - 9. Aluminum's symbol is Al, gold's symbol is Au, and carbon's symbol is C.

Answer:

1. True
2. a. Elements

b. Compounds

1. A pure substance that cannot be broken down into simpler substances by chemical means.
2. True
3. Because all of its atoms have the same number of protons, which defines the element's identity.
4. b. oxygen, d. nitrogen
5. b. Al
6. c. Au
7. a. C