Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsA. From Elements to Compounds

1. Compounds are chemical combinations of two or

more .

2. Compounds and the elements that form them often have very different chemical

and physical .

3. Atoms can bond to form compounds by valence

electrons.

4. A(n) is a group of chemical symbols and numbers that

represent the elements and the numbers of atoms of each element in a compound.

5. The letters in a chemical formula represent .

6. show the shape and appearance of the arrangement of

atoms in a compound.

B. Covalent Bonds—Electron Sharing

1. A(n) is a chemical bond formed when two or more

atoms share one or more pairs of valence electrons.

2. When forming water, valence electrons are between

oxygen and hydrogen atoms, thereby forming covalent bonds to make three stable

atoms.

C. Covalent Compounds

1. A(n) is a group of atoms held together by covalent

bonding that acts as an independent unit.

2. generally have low melting points and low boiling

points. They are conductors of electricity.

a. In a hydrogen molecule, a(n) covalent bond forms

when each atom shares its valence electrons with the other.

b. In a carbon dioxide molecule, a double covalent bond forms when the carbon

atom shares pairs of valence electrons with each

oxygen atom.

Elements and Chemical Bonds 27

Lesson Outline

Name Date Class

Lesson Outline continued

c. In a(n) covalent bond, three pairs of valenceelectrons are shared between two atoms.

d. covalent bonds are stronger than

covalent bonds, which are stronger than single

covalent bonds.

3. In a covalent bond, one atom can attract the shared electrons more

than the other atom can.

a. In a molecule of water, the atom attracts the

electrons more strongly than each hydrogen atom does.

b. Because the electrons have a slight negative charge, there is a slight negative

charge near the atom; there is a slight

charge near the hydrogen atoms.

c. A molecule that has a slight positive end and a slight negative end because of

unequal sharing of electrons is a(n) .

d. Polar molecules, such as sugar and water, easily inone another because of the attraction of opposite charges.

4. Molecules made up of atoms of the same element are because the atoms are identical. So, they share electrons equally.

28 Elements and Chemical Bonds

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsDirections: On the line before each statement, write T if the statement is true or F if the statement is false.

1. A compound is a substance that is composed of two or more different kindsof molecules.

2. Compounds are held together by chemical bonds.

3. CO2 is the structural formula of carbon dioxide.

4. When nonmetals combine with other nonmetals, they usually form covalentbonds.

5. A covalent bond is a chemical bond formed when two or more atoms shareone or more pairs of valence electrons.

6. A molecule is a group of atoms held together by covalent bonding that acts asan independent unit.

7. Compounds formed with covalent bonds usually have high melting andboiling points.

8. Compounds formed with covalent bonds are good conductors of electricity.

9. A polar molecule has a slight positive end and a slight negative end because ofthe unequal sharing of electrons.

10. Water is an example of a polar molecule.

30 Elements and Chemical Bonds

Content Practice A

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsDirections: On each line, write the term that correctly completes each sentence.

1. is the chemical formula of carbon dioxide.

2. One carbon dioxide molecule consists of carbon atom(s)

and oxygen atom(s).

3. When nonmetals form compounds by joining with other nonmetals, they tend to

establish bonds.

4. A(n) is a group of atoms held together by covalent bonding

that acts as an independent unit.

5. These compounds are usually or

at room temperature.

6. These compounds usually have low and

points.

7. In addition, they are poor conductors of .

8. A molecule that has a slight positive end and a slight negative end is called a(n)

molecule.

Elements and Chemical Bonds 31

Content Practice B

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsDirections: Use your textbook to answer each question.

1. A chemical formula represents a substance called a compound. Forexample, the chemical formula for table salt is NaCl. The chemicalcompound for water is H2O.What does a chemical formula tell you? What information about the compound is notpart of a chemical formula?

2. When nonmetal atoms join with other nonmetal atoms, they tend to formcovalent bonds.What makes nonmetals more likely to form covalent bonds?

3. A molecule is a group of atoms held together by covalent bonding that actsas an independent unit.Which properties do molecules usually share?

4. Charges on polar molecules affect the properties of the molecule.What is a polar molecule?

32 Elements and Chemical Bonds

School to Home

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsKey Concept How do elements differ from the compounds they form?

Directions: Complete this spider map by choosing terms and phrases from the word bank and writing them inthe correct spaces. On each top line, give the name of the model. On each bottom line, give its main function. Themap has been started for you.

ball-and-stick model electron dot diagramshows elements and shared pairs of electrons shows elements and valence electronsshows number of atoms in elements structural formula

Directions: Answer the question on the lines provided.

7. In a chemical formula, such as H2O (water), what does a small number next to anelement’s symbol tell you?

Elements and Chemical Bonds 33

Key Concept Builder

chemical formula

1.

2.

3.

DescribingChemical

Compounds

4.

5.

6.

shows bond angles

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsKey Concept What are some common properties of a covalent compound?

Directions: This diagram is a schematic drawing of the top six rows of the periodic table. Use the diagram toanswer each question on the lines provided.

1. Which elements are in the shaded area?

2. What kind of bonds do these elements tend to make when they combine with oneanother?

3. What is the definition of this kind of bond?

4. Which element located outside the shaded area forms many of this same kind of bond?

5.Where is that element in the diagram?

Key Concept Builder

34 Elements and Chemical Bonds

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsKey Concept What are some common properties of a covalent compound?

Directions: Put a check mark on the line before each property that is typical of a covalent compound.

1. liquid or gas at room temperature

2. metallic luster

3. low melting point

4. always solid at room temperature

5. poor conductor of electricity

6. very high boiling point

7. chemically unstable

8. made up of molecules

Directions: On the line before each description, write S if it is held together by a single bond, D if it is heldtogether by a double bond, and T if it is held together by a triple covalent bond.

9. molecular nitrogen (N2)

10. molecular hydrogen (H2)

11. carbon dioxide (CO2)

Elements and Chemical Bonds 35

Key Concept Builder

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsTrue or FalseDirections: On the line before each statement, write T if the statement is true or F if the statement is false.

1. A compound can have different chemical and physical properties than thoseof the elements it is made from.

2. A chemical formula shows the total number of atoms in a sample of acompound.

3. A molecule is a group of atoms held together by covalent bonding that acts asan independent unit.

4. A polar molecule is one that has equal electron attraction between atoms.

Multiple ChoiceDirections: On the line before each question or statement, write the letter of the correct answer.

5. In the chemical formula H2O, how many atoms of oxygen are represented?A. oneB. twoC. three

6. Which compound is a polar molecule?A. H2

B. H2OC. CO2

7. A double covalent bond is created whenA. two atoms share one pair of valence electrons.B. two atoms share bonds with four other atoms.C. two atoms share two pairs of valence electrons.

40 Elements and Chemical Bonds

Lesson Quiz A

Name Date Class

LESSON 2

Compounds, Chemical Formulas, and Covalent BondsCompletionDirections: On each line, write the term that correctly completes each sentence.

1. A(n) can have different chemical and physical propertiesthan those of the elements it is made from.

2. A(n) is a group of chemical symbols and numbers thatrepresent the elements and the numbers of atoms of each element that make up acompound.

3. A(n) is a group of atoms held together by covalent bondingthat acts as an independent unit.

4. A polar molecule has a slight charge near the atom thatattracts the shared electron more strongly.

Short AnswerDirections: Respond to each statement on the lines provided.

5. List the types and numbers of atoms represented in the chemical formula formethane, CH4.

6. Describe how polar and nonpolar liquids can be used to dissolve different substances.

7. Explain how double and triple covalent bonds occur.

Elements and Chemical Bonds 41

Lesson Quiz B