COVALENT BONDS

Ch. 8 Study Guide

1. How do you determine the number of valence electrons in an element?

1. Group # = # of valence electrons

2. What is a covalent bond?

Atoms held together by sharing electrons

3. Compare and contrast ionic and covalent bonds.

Ionic Covalent

Prefix naming

Share electrons

Close electroneg

a-tivity

-ide ending

Lose or gain electrons

octet

Large difference in electronegativity

4. Give an example of a molecular formula, perspective drawing, a structural formula, and a ball-and-stick molecular model.

Molecular Formula NH3 (g)

Structural Formula

Space-filling molecular model

Ball-and –stick molecular model

Perspective drawing

NH

HH

5. How does the octet rule apply to covalent bonding?

Elements will share electrons in order to have 8 electrons on their outer most energy level.

6. How do electron dot structures represent shared electrons?

Each pair of electrons (one from each atom) represents a single bond

If 2 electrons are donated by each atom then a double bond is formed.

If 3 electrons are donated by each atom then a triple bond is formed.

Circles show the electrons being shared

7. Draw the electron dot structure for the following molecules:

• H20 b. CH4

8. How do atoms form single, double, and triple covalent bonds?

Single bond= one electron from each atomDouble bond= two electrons from each atomTriple bond= three electrons from each atom

9. Do all of the electrons in an atom bond with those of another atom? What are the

two different pairs called?

Not all electrons are involved in a bond Non-bonding pairs Bonding paris

10. What is the VSEPR theory?

The repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible

11. Apply the VSEPR theory to draw the following molecules geometrically.

• PF5

• H2S

• HCN

12. Compare and contrast nonpolar and polar bonds.

-ide ending

Lose or gain electrons

polar nonpolar

Electrons are pulled toward one element

Electrons shared equally

Valence electrons

CH4

HCl

Pull on electrons

13. What is electronegativity?

The ability of an element to attract electrons

14. What is the trend of Electronegativity on the periodic table?

Lower left hand corner has the lowest electronegativity

Upper right hand corner has the highest electronegativity

15. List 2 ways you can tell if a molecule is polar or nonpolar.

Polar molecule has one end that is slightly negative and the other end is slightly positive

0.0-0.4- nonpolar covalent H-H

0.4-1.0- moderately polar covalent H-Cl

1.0-2.0- very polar covalent H-F

≥2.0 Ionic Na+Cl-

16. Determine whether the following molecules are polar or nonpolar.

H2S

SO3

17. List the prefixes used for naming covalent compounds.

MonoDiTriTetraPentaHexaHeptaOcta

18. Name the following covalent compounds:

SCl4 Si2Br6

19. Write the formula for the following compounds:

A. carbon tetrabromide- CBr4

B. diphosphorus trioxide- P2O3

20. Explain how polarity applies to paper chromatography.

The more polar the material the more it will travel up the chromatography paper.

21.Explain the term “like dissolves like”

A polar solute will dissolve a polar solventA nonpolar solute will dissolve a polar solvent

22. What is hydrogen bonding?

When hydrogen bonds with a very electronegative element it is polar

hydrogen will appear positiveThe hydrogen is then attracted to another

molecule that is also polar The hydrogen will bond to the end that

appears negative