1. 7 LOOKING BACK KEY CONCEPTS SUMMARY
CHAPTER 7
KEY CONCEPTS SUMMARY
Elements can combine to form compounds.
Atoms can join together with the same or different atoms to form molecules.
Molecular elements consist of only one type of element.
Molecular compounds consist of two or more different types of elements.
Ionic compounds consist of charged particles called ions.
Rust is an example of an ionic compound.
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2. 7 LOOKING BACK KEY CONCEPTS SUMMARY
CHAPTER 7
KEY CONCEPTS SUMMARY
Metals and non-metals combine to form ionic compounds. Non-metals combine to form molecules.
Metals lose electrons and become cations.
Non-metals gain electrons and become anions.
Cations and anions have opposite charges, so they attract each other and form ionic compounds.
Non-metals form covalent bonds with other non-metals by sharing electrons to form molecular compounds.
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3. 7 LOOKING BACK KEY CONCEPTS SUMMARY
CHAPTER 7
KEY CONCEPTS SUMMARY
Some useful compounds have social, environmental, and economic impacts.
DDT and PCBs bioaccumulate and cause health problems for humans and animals
Compounds such as plastics pose disposal problems because they do not biodegrade.
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4. 7 LOOKING BACK KEY CONCEPTS SUMMARY
CHAPTER 7
KEY CONCEPTS SUMMARY
Compounds can break apart into simpler substances.
Hydrogen peroxide easily decomposes into water (H2O) and oxygen (O2).
The oxygen released from the decomposition of hydrogen peroxide reacts with other chemicals, often producing a bleaching effect.
The decomposition of biodegradable materials is an example of compounds breaking down into simpler substances.
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5. 7 LOOKING BACK KEY CONCEPTS SUMMARY
CHAPTER 7
KEY CONCEPTS SUMMARY
Molecular models are used to represent molecules.
Models help us visualize the three-dimensional shapes of molecules.
Atoms combine with other atoms to form molecules.
All the atoms of an element form the same number of bonds.
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6. 7 LOOKING BACK KEY CONCEPTS SUMMARY
CHAPTER 7
KEY CONCEPTS SUMMARY
Simple chemical tests can identify common gases.
Oxygen gas can be identified by more vigorous burning.
Hydrogen gas can be identified by a “pop” sound heard when hydrogen atoms combine with oxygen atoms to form water vapour.
Carbon dioxide can be identified by the white solid it produces when it reacts with limewater.
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7. QUIZ
CHAPTER 7
MULTIPLE CHOICE
For each question, select the best answer from the four alternatives.
1. Propane gas, C3H8, is used in barbecues. What is the total number of atoms in one molecule of propane gas?
(a) 3
(b) 8
(c) 5
(d) 11
2. Which one of the following chemical formulas does not represent a molecular element?
(a) N2
(b) O2
(c) S8
(d) H2O

8. QUIZ
CHAPTER 7
MULTIPLE CHOICE
For each question, select the best answer from the four alternatives.
3. A magnesium ion has 12 protons and 10 electrons. What is the charge of a magnesium ion?
(a) –1
(b) –2
(c) +1
(d) +2
4. Which one of the following is an ionic compound?
(a) CO2
(b) H2O2
(c) KI
(d) C12H22O11

9. QUIZ
CHAPTER 7
FILL IN THE BLANKS
Fill in the blanks with a that correctly completes the sentence.
5. In general, a metallic atom and a non-metallic atom form a(n) _______________ compound, and a non-metallic atom and a non-metallic atom form a(n) _______________ compound.
6. Hydrogen peroxide decomposes into _______________ and _______________.
MATCHING
Match the following examples with the appropriate term. 7.
molecular (or covalent), oxygen, ionic, water

10. QUIZ
CHAPTER 7
SHORT ANSWER
8. What type of compound will form when the following elements combine?
(a) magnesium and chlorine
(b) sulphur and oxygen
(c) carbon and hydrogen
(d) iron and oxygen
9. Explain what happens when potassium and iodine form an ionic compound.
10. Explain what happens when hydrogen and oxygen form a water molecule.

11. 7 QUIZ ANSWERS MULTIPLE CHOICE
CHAPTER 7
MULTIPLE CHOICE
1. Propane gas, C3H8, is used in barbecues. What is the total number of atoms in one molecule of propane gas?
(a) 3
(b) 8
(c) 5
(d) 11
2. Which one of the following chemical formulas does not represent a molecular element?
(a) N2
(b) O2
(c) S8
(d) H2O

12. 7 QUIZ ANSWERS MULTIPLE CHOICE
CHAPTER 7
MULTIPLE CHOICE
3. A magnesium ion has 12 protons and 10 electrons. What is the charge of a magnesium ion?
(a) –1
(b) –2
(c) +1
(d) +2
4. Which one of the following is an ionic compound?
(a) CO2
(b) H2O2
(c) KI
(d) C12H22O11

13. 7 QUIZ ANSWERS FILL IN THE BLANKS
CHAPTER 7
FILL IN THE BLANKS
5. In general, a metallic atom and a non-metallic atom form a(n) ionic compound and a non-metallic atom and a non-metallic atom form a(n) molecular (or covalent) compound.
6. Hydrogen peroxide decomposes into water and oxygen.

14. 7 QUIZ ANSWERS SHORT ANSWER
CHAPTER 7
SHORT ANSWER
8. What type of compound will form when the following elements combine?
(a) magnesium and chlorine ionic
(b) sulphur and oxygen molecular (or covalent)
(c) carbon and hydrogen molecular (or covalent)
(d) iron and oxygen ionic
9. Explain what happens when potassium and iodine form an ionic compound.
Potassium atoms lose an electron to form +1 potassium ions, and iodine atoms gain an electron to form –1 chloride ions. These ions have opposite charges, so they attract one another and form the ionic compound potassium iodide.
10. Explain what happens when hydrogen and oxygen form a water molecule, H2O.
The oxygen atom shares an electron with each hydrogen atom. This gives each of the hydrogen atoms two electrons in their outermost electron orbit and gives the oxygen atom eight electrons in its outermost electron orbit.