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Chapter 3 Section 2 Notes
Compounds
Compounds: Made of Elements
A compound _________________________________________________________________________
______________________________________________________________
When atoms react they form a ____________
A particle of a compound is a molecule. Molecules of compounds are formed when ___________ of
______________ or more _______________ join together.
In Figure 1, you see magnesium reacting with oxygen. A compound
called magnesium oxide is forming.
The compound is a new pure substance. It is different from the elements that
make it up. Most of the substances that you see every day are
compounds. Table 1 lists some familiar examples.
Figure 1 As magnesium burns, it reacts with oxygen and forms the compound
magnesium oxide.
Table 1 Familiar Compounds
Compound
Table salt
Water
Vinegar
Carbon dioxide
Baking soda
Elements combined
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The Ratio of Elements in a Compound
Elements do not ___________ form compounds.
Elements join in a specific ________________ (comparison) according to their masses to form a
compound.
For example, the ratio of the mass of hydrogen to the mass of oxygen in water is 1 to 8. This
mass ratio can be written as 1:8. This ratio is always the same. Every sample of water has a 1:8
mass ratio of hydrogen to oxygen.
Stop and Jot: If a sample of a compound has a different mass ratio of hydrogen to oxygen?
Is it water?
Properties of Compounds
Compounds have physical properties:
Physical properties include ________________, ______________, and ______________.
Compounds can also be identified by their different chemical properties.
Some compounds react with acid.
For example:
calcium carbonate (__________), reacts with acid.
hydrogen peroxide, react when
_____________________________.
Stop and Jot: What are three physical properties
used to identify compounds?
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COMPOUNDS: MADE OF ELEMENTS
_____ 2. Which of the following is NOT true about compounds?
a. Compounds are combinations of elements that join in specific ratios according to their
masses.
b. The mass ratio of a specific compound is always the same.
c. Compounds are random combinations of elements.
d. Different mass ratios mean different compounds.
3. When two or more elements are joined by chemical bonds to form a new pure substance, we call that
new substance a(n) ______________________
4. A compound is different from the ______________________ that reacted to form it.
PROPERTIES OF COMPOUNDS
_____ 5. Which of the following statements is true about the properties of compounds?
a. A property of all compounds is to react with acid.
b. Each compound has its own physical properties.
c. Compounds cannot be identified by their chemical properties.
d. A compound has the same properties as the elements that form it.
6. Sodium and chlorine can be extremely dangerous in their elemental form. How is it possible that we can
eat them in a compound?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
Match the correct description with the correct term. Write the letter in the space provided.
_____ 7. a poisonous, greenish yellow gas
a. sodium chloride
b. chlorine
_____ 8. table salt
_____ 9. a soft, silvery white metal that reacts
violently with water
c. sodium