1. Unit 2: SMELLS Molecular Structure and Properties
Living By Chemistry
Unit 2: SMELLS
Molecular Structure and Properties

2. In this unit you will learn:
how atoms form molecules
to predict the smell of a compound
to interpret molecular models
how the nose detects different molecules

3. Day 15 ChemCatalyst
1. What do you think is happening when you smell something?
2. Why do you think we have a sense of smell?

4. Day 16 ChemCatalyst
Will any of the molecules shown on the following slide have similar smells? Explain your thinking.

5. Key Question
What does chemistry have to do with smell?
How can molecules with the same molecular formula be different?
What are the rules for drawing structural formulas?

6. You will be able to:
detect patterns in chemical formulas and relate these patterns to a molecular property
create a hypothesis based on analysis of data
describe the difference between structural formulas and molecular formulas
recognize isomerscreate accurate structural formulas from molecular formulas
identify and differentiate between isomers and molecules oriented differently in space
explain and utilize the HONC 1234 rule

7. Prepare for the Activity
Work in groups of four.
Molecular formula: The chemical formula of a molecular substance, showing the types of atoms in each molecule and the ratios of those atoms to one another.

8. Prepare for the Activity (cont.)
Chemicals may have very strong odors or be caustic. When smelling, don’t sniff directly from the container. Instead, use a wafting technique (use your hand to draw air toward you).

9. Discussion Notes
A possible hypothesis is “The smell of a substance can be predicted if you know its name and/or its chemical formula.”

10. Discussion Notes
Even though the molecules in vials G and H have identical molecular formulas, they have different smells and therefore must be different somehow.
A structural formula is a two-dimensional drawing of a molecule showing how the atoms in a molecule are connected.

11. Discussion Notes (cont.)
Structural formula: A drawing or diagram that a chemist uses to show how the atoms in a molecule are connected. Each line represents a covalent bond.
There are several ways to draw the same structural formula without changing the identity of the molecule.

12. Discussion Notes (cont.)
When two molecules have the same molecular formula but different structural formulas, they are called isomers of each other.
Isomers: Molecules with the same molecular formula but different structural formulas.

13. Discussion Notes (cont.)

14. Discussion Notes (cont.)
Molecules can smell different even if they have the same molecular formula.
Molecules can smell similar even if they have different molecular formulas.

15. Discussion Notes
The HONC 1234 rule is a way to remember the bonding tendencies of hydrogen, oxygen, nitrogen, and carbon atoms in molecules. Hydrogen tends to form one bond, oxygen two, nitrogen three and carbon four.
When trying to decide whether two structures represent the same molecule, you must check how the atoms are connected.

16. Wrap Up What does chemistry have to do with smell?
Smell appears to be related to molecular formula and chemical name.

17. Wrap Up
How can molecules with the same molecular formula be different?
Structural formulas show how the atoms in a molecule are connected.
A molecular formula can be associated with more than one structural formula.
Isomers are molecules with identical molecular formulas but different structural formulas.
The smell of a molecule is a property that appears to be related to its structure.

18. Wrap Up What are the rules for drawing structural formulas?
The HONC 1234 rule indicates how many times hydrogen, oxygen, nitrogen, and carbon atoms tend to bond.
When a molecule is oriented differently in space, it is still the same molecule.

19. Check-in
How would you expect a compound with the molecular formula C8H16O2 to smell? Explain.
How sure are you of your prediction?

20. extra ChemCatalyst
Examine the molecules on the following slides. What patterns do you see in the bonding of atoms of hydrogen, oxygen, carbon, and nitrogen?

21. Day 17 ChemCatalyst These diagrams are called Lewis dot symbols.
Look at the Lewis dot symbols and answer the questions.
What is the relationship between the number of dots, the number of valence electrons, and the HONC 1234 rule?
Create a Lewis dot symbol for fluorine, F. How many bonds will fluorine make?

22. Key Question How do atoms bond to form molecules?
How does one atom bond to another in a molecule?
How do atoms bond to form molecules?

23. You will be able to:
create accurate structural formulas using Lewis dot symbols
describe the type of bonding found in molecular substances
explain the chemistry behind the HONC 1234 rule
apply the octet rule to predict bonding in molecules
draw Lewis dot structures and structural formulas for molecules that contain double and triple bonds

24. Prepare for the Activity
Work in groups of four.
Lewis dot symbol: A diagram that uses dots to show the valence electrons of a single atom.

25. Prepare for the Activity (cont.)
Each puzzle piece contains the correct number of valence electrons for that atom. It also contains the appropriate number of tabs for bonding.

26. Prepare for the Activity
Work in groups of four.
Octet rule: Nonmetal atoms combine so that each atom has a total of eight valence electrons by sharing electrons.

27. Prepare for the Activity (cont.)
Each atom in the molecule has an “octet” of valence electrons. Note that the hydrogen atoms do not follow the octet rule. They have a total of two electrons, similar to the noble gas helium, He.
After bonding, each chlorine atom has a total of eight valence electrons surrounding it.
Cl2
PCl3
H2S

28. Discussion Notes
You can use Lewis dot symbols to create Lewis dot structures.
Lewis dot structure: A diagram that uses dots to show the valence electrons of a molecule.

29. Discussion Notes (cont.)
A covalent bond is the sharing of a pair of electrons between two nonmetal atoms.
Bonded pair: A pair of electrons that are shared in a covalent bond between two atoms.

30. Discussion Notes (cont.)
Some valence electrons are not involved in bonding.
Lone pair: A pair of valence electrons not involved in bonding within a molecule. The two electrons belong to one atom.

31. Discussion Notes
The HONC 1234 rule and the octet rule both help you figure out Lewis dot structures and structural formulas.
Both the HONC 1234 rule and the octet rule can be satisfied by using double and triple bonds appropriately.
It is not possible to create a triple-bonded oxygen compound, according to the HONC rule.
There are exceptions to the bonding rules laid out here.

32. Wrap Up How does one atom bond to another in a molecule?
A covalent bond is a bond in which two atoms share a pair of valence electrons.
Lewis dot symbols show the valence electrons in an atom and are used to predict bonding in a molecule.

33. Wrap Up (cont.)
In a Lewis dot structure, a pair of electrons that are shared in a covalent bond is called a bonded pair. Pairs of electrons that are not involved in bonding and belong to one atom are referred to as lone pairs.
The HONC 1234 rule indicates how many electrons are available for bonding in atoms of hydrogen, oxygen, nitrogen, and carbon.

34. Wrap Up How do atoms bond to form molecules?
Elements form covalent bonds by sharing electrons until each atom has eight valence electrons. This is called the octet rule. Hydrogen is an exception. It forms bonds such that it has two valence electrons.
Atoms can form double and triple bonds to satisfy the octet rule.
When covalent bonds form, each atom resembles a noble gas in its electron configuration.

35. Day 18 ChemCatalyst
Draw the Lewis dot structure for the two covalently bonded molecules shown here. Explain how you arrived at your answer.
a. Cl2 b. O2

36. Check-in
1. One of these compounds has multiple bonds in it. Which one is it? Explain.
C4H10 C4H6
2. Draw one possible structural formula for C4H6.

37. Day 19 ChemCatalyst
Consider these compounds. List at least three differences and three similarities between the two molecules.
Molecule Molecule 2