Covalent Bonding Practice Quiz

Instructions

For each molecule:

Fill in the valence electron table (electrons each atom has and needs)
Calculate the total valence electrons
Draw the complete Lewis structure showing all bonds and lone pairs

Remember: Bonds needed = 8 - valence electrons (except H, which needs only 2)

Quick Reference - Valence Electrons by Group:

H = 1 valence e⁻, needs 1 more (wants 2 total)
C (Group 14) = 4 valence e⁻, needs 4 more
N (Group 15) = 5 valence e⁻, needs 3 more
O, S (Group 16) = 6 valence e⁻, needs 2 more
F, Cl, Br, I (Group 17) = 7 valence e⁻, needs 1 more

Section A Simple Molecules

Problem 1: Methane (CH₄)

Draw the Lewis structure for methane.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
C	1	______	______	______
H	4	______	______	______

Total valence electrons: ______ + ______ = ______

Central atom: ______

Draw your Lewis structure here

Problem 2: Water (H₂O)

Draw the Lewis structure for water.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
H	2	______	______	______
O	1	______	______	______

Total valence electrons: ______ + ______ = ______

Central atom: ______
How many lone pairs on oxygen? ______

Draw your Lewis structure here

Problem 3: Ammonia (NH₃)

Draw the Lewis structure for ammonia.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
N	1	______	______	______
H	3	______	______	______

Total valence electrons: ______ + ______ = ______

Central atom: ______
How many lone pairs on nitrogen? ______

Draw your Lewis structure here

Problem 4: Hydrogen Fluoride (HF)

Draw the Lewis structure for hydrogen fluoride.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
H	1	______	______	______
F	1	______	______	______

Total valence electrons: ______ + ______ = ______

How many lone pairs on fluorine? ______

Draw your Lewis structure here

Problem 5: Hydrogen Sulfide (H₂S)

Draw the Lewis structure for hydrogen sulfide.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
H	2	______	______	______
S	1	______	______	______

Total valence electrons: ______ + ______ = ______

Central atom: ______
How many lone pairs on sulfur? ______

Draw your Lewis structure here

Section B Carbon Compounds

Problem 6: Methanol (CH₃OH)

Draw the Lewis structure for methanol (wood alcohol).

Hint: Carbon is bonded to 3 hydrogens and 1 oxygen. The oxygen is bonded to 1 hydrogen.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
C	1	______	______	______
H	4	______	______	______
O	1	______	______	______

Total valence electrons: ______ + ______ + ______ = ______

How many lone pairs on oxygen? ______

Draw your Lewis structure here

Problem 7: Methylamine (CH₃NH₂)

Draw the Lewis structure for methylamine.

Hint: Carbon is bonded to 3 hydrogens and 1 nitrogen. The nitrogen is bonded to 2 hydrogens.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
C	1	______	______	______
H	5	______	______	______
N	1	______	______	______

Total valence electrons: ______ + ______ + ______ = ______

How many lone pairs on nitrogen? ______

Draw your Lewis structure here

Problem 8: Ethane (C₂H₆)

Draw the Lewis structure for ethane (two carbons bonded together).

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
C	2	______	______	______
H	6	______	______	______

Total valence electrons: ______ + ______ = ______

How many bonds does each carbon form? ______

Draw your Lewis structure here

Problem 9: Chloromethane (CH₃Cl)

Draw the Lewis structure for chloromethane.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
C	1	______	______	______
H	3	______	______	______
Cl	1	______	______	______

Total valence electrons: ______ + ______ + ______ = ______

How many lone pairs on chlorine? ______

Draw your Lewis structure here

Problem 10: Dichloromethane (CH₂Cl₂)

Draw the Lewis structure for dichloromethane.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
C	1	______	______	______
H	2	______	______	______
Cl	2	______	______	______

Total valence electrons: ______ + ______ + ______ = ______

How many total lone pairs in this molecule? ______

Draw your Lewis structure here

Section C More Compounds

Problem 11: Phosphine (PH₃)

Draw the Lewis structure for phosphine.

Hint: Phosphorus behaves like nitrogen!

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
P	1	______	______	______
H	3	______	______	______

Total valence electrons: ______ + ______ = ______

How many lone pairs on phosphorus? ______

Draw your Lewis structure here

Problem 12: Nitrogen Trifluoride (NF₃)

Draw the Lewis structure for nitrogen trifluoride.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
N	1	______	______	______
F	3	______	______	______

Total valence electrons: ______ + ______ = ______

Central atom: ______
How many lone pairs on nitrogen? ______
How many lone pairs on each fluorine? ______

Draw your Lewis structure here

Problem 13: Oxygen Difluoride (OF₂)

Draw the Lewis structure for oxygen difluoride.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
O	1	______	______	______
F	2	______	______	______

Total valence electrons: ______ + ______ = ______

Central atom: ______
How many lone pairs on oxygen? ______

Draw your Lewis structure here

Problem 14: Silicon Tetrafluoride (SiF₄)

Draw the Lewis structure for silicon tetrafluoride.

Hint: Silicon behaves like carbon!

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
Si	1	______	______	______
F	4	______	______	______

Total valence electrons: ______ + ______ = ______

How many lone pairs on silicon? ______
How many lone pairs on each fluorine? ______

Draw your Lewis structure here

Section D Challenge Problems

Problem 15: Ethanol (C₂H₅OH)

Draw the Lewis structure for ethanol (drinking alcohol).

Hint: Two carbons bonded together; one carbon has 3 H's, the other has 2 H's and is bonded to an OH group.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
C	2	______	______	______
H	6	______	______	______
O	1	______	______	______

Total valence electrons: ______ + ______ + ______ = ______

Draw your Lewis structure here

Problem 16: Hydrogen Peroxide (H₂O₂)

Draw the Lewis structure for hydrogen peroxide.

Hint: The two oxygens are bonded to each other, and each oxygen is also bonded to one hydrogen.

Atom	How many?	Valence e⁻ each	Total from this atom	Bonds needed (each)
H	2	______	______	______
O	2	______	______	______

Total valence electrons: ______ + ______ = ______

How many lone pairs on each oxygen? ______

Draw your Lewis structure here

Section E Conceptual Questions

Problem 17

What is the difference between an ionic bond and a covalent bond?

Write your answer here

Problem 18

Why does carbon typically form 4 bonds while oxygen typically forms 2 bonds? Use valence electrons in your explanation.

Write your answer here

Problem 19

What is electronegativity? Explain it in your own words.

Write your answer here

Problem 20: Isomers

What are isomers? Explain in your own words.

Write your answer here

Problem 21: Isomers of C₂H₆O

The molecular formula C₂H₆O has two different isomers. Draw the Lewis structure for BOTH isomers.

Hint: In one isomer, the oxygen is at the end of the chain (alcohol). In the other, the oxygen is in the middle (ether).

Isomer 1: Ethanol (CH₃CH₂OH)

Oxygen at the END

Draw here

Isomer 2: Dimethyl Ether (CH₃OCH₃)

Oxygen in the MIDDLE

Draw here

Problem 22

Complete the table below:

Molecule	Total Valence e⁻	# Single Bonds	# Lone Pairs (total)
H₂O
CH₄
NH₃
HF
H₂S

Covalent Bonding Practice Quiz

Instructions

Section A Simple Molecules

Section B Carbon Compounds

Section C More Compounds

Section D Challenge Problems

Section E Conceptual Questions

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