Unit 1Chemistry 350 Organic Chemistry I
Study Guide :: Unit 2
Polar Covalent Bonds; Acid and Bases
Unit Preview
This unit provides a review of the more advanced material covered in a standard introductory chemistry course through a discussion of the following topics:
- the drawing and interpretation of organic chemical structures.
- the use of ball-and-stick molecular models.
- the concept of formal charge.
- the use of electronegativities to determine bond polarity, and the application of this knowledge to determining whether a given molecule possesses a dipole moment.
- the Brønsted-Lowry and Lewis definitions of acids and bases, acidity constants and acid-base reactions.
The unit begins with an Entry Level Test designed to allow you to assess your mastery of the material. If you answer all the test questions correctly, proceed to Unit 3; if you correctly answer 14 or more questions, review the topics that posed problems and then go on to Unit 3; if you give correct answers to fewer than 14 questions, work through Unit 2.
Download Unit 2 Entry Level Test
Download Unit 2 Entry Level Test Answer Key
2.1 Polar Covalent Bonds: Electronegativity
Objectives
After completing this section, you should be able to
- describe how differences in electronegativity give rise to bond polarity.
- arrange a given series of the elements most often encountered in organic chemistry (C, H, O, S, P and the halogens) in order of increasing or decreasing electronegativity, without referring to a table of electronegativities.
- predict the positive and negative ends of a given bond formed between any two of the elements listed in Objective 2, above, without the use of a table of electronegativities or a periodic table.
- predict the positive and negative ends of a given bond formed between any two elements not listed in Objective 2, above, using a periodic table.
Learning Activities
Read 2.1 Polar Covalent Bonds: Electronegativity and do any associated exercises.
2.2 Polar Covalent Bonds: Dipole Moments
Objectives
After completing this section, you should be able to
- explain how dipole moments depend on both molecular shape and bond polarity.
- predict whether a molecule will possess a dipole moment, given only its molecular formula or Kekulé structure.
- use the presence or absence of a dipole moment as an aid to deducing the structure of a given compound.
Learning Activities
Read 2.2 Polar Covalent Bonds: Dipole Moments and do any associated exercises.
2.3 Formal Charges
Objectives
After completing this section, you should be able to
- determine which atoms, if any, of a given simple compound (e.g., HNO3, $\ce{\sf{CH2=N=N}}$, $\ce{\sf{CH3-N#C}}$) carry formal charges, and apply the principles used to more complex examples. [The Lewis structure, Kekulé structure or molecular formula would normally be provided.]
- draw the Lewis structure, the Kekulé structure, or both, of a compound of known molecular formula in which certain atoms possess a formal charge.
Learning Activities
Read 2.3 Formal Charges and do any associated exercises.
2.4 Resonance
Objectives
No objectives have been identified for this section.
Learning Activities
Read 2.4 Resonance and do any associated exercises.
2.5 Rules for Resonance Forms
Objective
After completing this section, you should be able to use the concept of resonance to explain structural features of certain species; for example, why all of the carbon-oxygen bonds in the carbonate ion are the same length. Note: This particular compound is discussed in further detail in Section 2.6.
Learning Activities
Read 2.5 Rules for Resonance Forms and do any associated exercises.
2.6 Drawing Resonance Forms
Objective
After completing this section, you should be able to draw all possible resonance structures for a given species.
Learning Activities
Read 2.6 Drawing Resonance Forms and do any associated exercises.
2.7 Acids and Bases: The Brønsted-Lowry Definition
Objectives
After completing this section, you should be able to
- state the Brønsted-Lowry definition of an acid and a base.
- identify the Brønsted-Lowry acid and base in a given acid-base reaction.
Learning Activities
Read 2.7 Acids and Bases: The Brønsted-Lowry Definition and do any associated exercises.
2.8 Acid and Base Strength
Objectives
After completing this section, you should be able to
- write the expression for the Ka of any given weak acid, HA.
- convert a given Ka value into a pKa value, and vice versa.
- arrange a series of acids in order of increasing or decreasing strength, given their Ka or pKa values.
- arrange a series of bases in order of increasing or decreasing strength, given the Ka or pKa values of their conjugate acids.
Learning Activities
Read 2.8 Acid and Base Strength and do any associated exercises.
2.9 Predicting Acid-Base Reactions from pKa Values
Objective
After completing this section, you should be able to predict the acid-base reactivity of a system using pKa values.
Learning Activities
Read 2.9 Predicting Acid-Base Reactions from pKa Values and do any associated exercises.
2.10 Organic Acids and Organic Bases
Objective
After completing this section, you should be able to identify an organic compound as being acidic or basic, given its structure.
Learning Activities
Read 2.10 Organic Acids and Organic Bases and do any associated exercises.
2.11 Acids and Bases: The Lewis Definition
Objectives
After completing this section, you should be able to
- state the Lewis definition of an acid and a base.
- identify a given compound as being a Lewis acid or Lewis base, given its Lewis structure or its Kekulé structure.
Learning Activities
Read 2.11 Acids and Bases: The Lewis Definition and do any associated exercises.
2.12 Noncovalent Interactions Between Molecules
Objectives
After completing this section, you should be able to
- identify the various intermolecular forces operating in a given organic compound.
- describe how intermolecular forces influence the physical properties, 3‑dimensional shape and structure of compounds.
Learning Activities
Read 2.12 Noncovalent Interactions Between Molecules and do any associated exercises.
2.13 Molecular Models
Objective
After completing this section, you should be able to use ball-and-stick molecular models to make models of simple organic compounds (e.g., ethane, ethylene, acetylene, ethanol, formaldehyde, acetone, acetic acid), given their Kekulé structures or molecular formulas.
Learning Activities
Read 2.13 Molecular Models and do any associated exercises.
Using a molecular model kit, try to model each of the compounds below.
ethanol,
formaldehyde (methanal),
acetone (propanone),
acetic (ethanoic) acid,