6.2 Covalent Compounds: (Pages 232-240)

Homework: Page 241 # 1, 4, 5, 7Key Concepts: (Page 241)

• Most simple covalent bonds are composed of linked or bonded atoms of different elements. These elements are usually two or more non-metals

• The attraction between molecules is much weaker than the attraction between oppositely charged ions in an ionic crystal.

• This contributes to the differences in the properties of ionic compounds and some covalent compounds.

• Many covalent compounds tend to have low melting points and low solubility in water, compared with ionic compounds.

• Many covalent compounds are also poor conductors of heat and electricity.

• Plastics are a large class of polymer covalent compounds. Their numerous uses include shopping bags, containers, and fabrics.

• There are, however, many environmental concerns associated with the use of plastics.

Covalent Bonds:

1. Which type of elements are covalent compounds composed of?

Only non-metals are combined to form covalent compounds.

2. What happens to electrons in a covalent bond?

Electrons are shared between elements.

Draw the Bohr-Rutherford models for water.

4. What is a molecule?

A molecule is the smallest discrete particle of a pure substance, which has one or more shared pairs of electrons.

5. What is the other term used for covalent compounds?

Covalent compounds are also called molecular compounds.

Prefixes for Covalent Compounds

Prefix Number Prefix Number

Mono 1 Hexa 6

Di 2 Hepta 7

Tri 3 Octa 8

Tetra 4 Nona 9

Penta 5 Deca 10

8. Explain how to name covalent compounds.

• The prefixes mono, di, tri, tetra, etc. are used to show the number of atoms in the compound.

Examples:• Dinitrogen monoxide – N2O

• Dinitrogen trioxide – N2O3

9. Name the following compounds:

a) Carbon trichloride (Monocarbon trichloride)

b) Trinitrogen pentaoxide

c) Carbon tetraoxide (Monocarbon tetraoxide)

d) Hexacarbon dioxide

e) Pentanitrogen trioxide

10. Identify the elements in each covalent compound and state the number of atoms

of each element. a) SiCl4b) SCl6c) N2C

d) C3F5

e) CO2

11. List some properties of covalent compounds:

• The attraction between molecules in a covalent compound are weak compared to ions (because you’re sharing electrons)

• Relatively low melting & boiling points • Relative softness in covalent compounds• Poor conductors of electricity and heat

12. What are plastics made of?• Plastics are made of molecular

compounds called polymers.

13. How are plastics classified?• Ethylene, a molecular compound

composed of hydrogen & carbon, is a common starting material for a class of plastics called polyethylenes.

12. Why might a city like Toronto consider imposing a change or ban

on plastic bags?They may pose a ban on plastic bags because:• Plastic bags are not biodegradable (they

cannot be broken down naturally by living organisms)

• The small, broken-down particles of the plastic bags contain toxic materials that can get into water & soil

13. Brainstorm a list of solutions to reduce the use of plastic bags.

• Use a cloth bag/reusable bag • Carry your purchases when possible• Use a shopping cart/trolley