Intermolecular Forces and Liquids and Solids — Define and Explain the Types of Intermolecular Forces
Question
Define the following and give an example of a molecule in which each occurs as the strongest intermolecular attraction:
- Dispersion force
- Dipole-dipole attraction
- Hydrogen bond
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- Dispersion force:
- Definition: A dispersion force is an intermolecular attraction that forms due to asymmetric electron distribution between temporary dipoles.
- Example: Br2
- Dipole-dipole attraction:
- Definition: A dipole-dipole attraction is an intermolecular attraction between 2 permanent dipoles; it results from an electrostatic attraction of the positive end of one polar molecule to the negative end of another polar molecule.
- Example: ICI
- Hydrogen bonds:
- Definition: A hydrogen bond is the electrostatic attraction between the partially positive hydrogen atom (when the hydrogen is bound to F, O, or N) in one molecule and the partially negative atom (F, O, or N) in another molecule
- Example: HF
Refer to Section 6.1: Intermolecular Forces (1).
Strategy Map
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| Strategy Map Steps |
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1. Identify if polarity plays a role with that type of force. This will help determine its cause.
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2. Identify the strength of the interaction.
Show/Hide HintThere are different types of dipole-dipole attractions. The strongest type of dipole-dipole attraction has its own name. |
| 3. Recall which molecules the interactions occur in. |
Solution
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a. Dispersion force
Definition: A dispersion force is an intermolecular attraction that forms due to asymmetric electron distribution between temporary dipoles.
Dispersion forces occur as an atom develops a temporary dipole moment when its electrons are distributed asymmetrically about the nucleus, and is then attracted to another atom with a temporary dipole moment. They are the intermolecular attraction which occurs between nonpolar molecules.
Example: Br2
b. Dipole-dipole attraction
Definition: A dipole-dipole attraction is an intermolecular attraction between 2 permanent dipoles, which results from an electrostatic attraction of the positive end of one polar molecule to the negative end of another polar molecule.
Example: ICI
c. Hydrogen bonds
Definition: A hydrogen bond is the electrostatic attraction between the partially positive hydrogen atom (when the hydrogen is bound to F, O, or N) in one molecule and the partially negative atom (F, O, or N) in another molecule.
The electrostatic attraction between the partially positive hydrogen atom in one molecule and the partially negative atom in another molecule gives rise to a very strong type of dipole-dipole interaction called a hydrogen bond.
Example: HF
Guided Solution
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The guided solution below will give you the reasoning for each step to get your answer, with reminders and hints.
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| Guided Solution Ideas |
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This question is a theory type problem that asks you to define 3 different types of intermolecular forces and provide 3 example molecule for each force.
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Recall your knowledge of polarity.
Show/Hide Don’t Forget!Polarity occurs when a molecule has an unsymmetrical net dipole. It will cause one atom to gain a partial positive charge and another to gain a partial negative charge. If the molecule exhibits constant polarity, you can expect its intermolecular interactions to be a form of dipole-dipole attraction. |
Why is there an attraction between 2 molecules? (think about magnets)
Show/Hide Think About This!Attraction between molecules occurs due to electrostatic attractions (when a negatively-charged atom is attracted to a positively-charged atom). Are some attractions stronger than others? Show/Hide Think About This!Intermolecular forces are weaker forces that occur between molecules. Their strength varies depending on the type of intermolecular force. Dispersion forces are the weakest, dipole-dipole attractions are stronger, and hydrogen bonds are a very strong type of dipole-dipole attraction |
| Complete Solution |
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| a. Dispersion force
A dispersion force is an intermolecular attraction that forms due to asymmetric electron distribution between temporary dipoles. Dispersion forces occur as an atom develops a temporary dipole moment when its electrons are distributed asymmetrically about the nucleus. A second atom can then be distorted by the appearance of the dipole in the first atom. The electrons of the second atom are attracted toward the positive end of the first atom, which sets up a dipole in the second atom. The net result is rapidly fluctuating, temporary dipoles that attract and are caused by one another. Dispersion forces can occur between all molecules. Electron clouds are constantly moving and attracting to other positive charges around them. For this reason, a momentary disturbance can cause a dispersion force between 2 or more molecules. Dispersion forces occur as an atom develops a temporary dipole moment when its electrons are distributed asymmetrically about the nucleus, and is then attracted to another atom with a temporary diploe moment. They are the intermolecular attraction which occurs between nonpolar molecules. Answer:
Show/Hide ResourceRefer to Section 6.1.2 Dispersion Forces (1). |
| b. Dipole-dipole attraction
A dipole-dipole attraction is an intermolecular attraction between 2 permanent dipoles, which results from an electrostatic attraction of the positive end of one polar molecule to the negative end of another polar molecule. Polar molecules have partially charged atoms due to unsymmetrical net dipoles. This negative partial charge can easily form an attraction to another partial positive charged atom. For example, the positive end of one polar molecule will be attracted to the negative end of another polar molecule. Answer:
Show/Hide ResourceRefer to Section 6.1.3 Dipole-Dipole Attractions (1). |
| c. Hydrogen bonds
A hydrogen bond is the electrostatic attraction between the partially positive hydrogen atom (when the hydrogen is bound to F, O, or N) in one molecule and the partially negative atom (F, O, or N) in another molecule. Hydrogen bonds form whenever a hydrogen atom is bonded to one of the more electronegative atoms, such as a fluorine, oxygen, or nitrogen atom. The electrostatic attraction between the partially positive hydrogen atom in one molecule and the partially negative atom in another molecule gives rise to a very strong type of dipole-dipole interaction called a hydrogen bond. Polarity is caused by electronegativity differences. Hydrogen has a very low electronegative and forms a very strong bond when paired with high electronegative atoms. When electronegativity differences occur, the higher electronegative atom will pull the shared electrons closer to itself. With hydrogen, the highly electronegative atom pulls the electrons closer to its nucleus and further from hydrogen’s nucleus, giving hydrogen a very strong positive charge. When 2 of these molecules come into contact, they will form a very strong attraction called a hydrogen bond. Answer:
Show/Hide ResourceRefer to Section 6.1.4 Hydrogen Bonding (1). |
Check Your Work
Think about what the terms mean and how the strength of intermolecular attraction varies with each type.
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Look at the type of molecule you have listed as the example for each intermolecular attraction—make sure it fits and would have that attraction as its dominant force. For the above examples, Br2 is nonpolar, ICl is a polar covalent molecule that cannot form hydrogen bonds, and HF is a polar covalent molecule that can form hydrogen bonds.
Does your answer make chemical sense?
Show/Hide Answer
Intermolecular forces are forces that occur between molecules. All molecules have intermolecular forces at some point. The types of forces they are influenced by are dependent on the properties of the molecule.
Dispersion forces are felt by all molecules as they are spontaneous and occur due to temporary charges of the moving electron clouds.
Polar molecules will experience dipole-dipole attractions and the strength of the polarity will determine the strength of the interaction.
Hydrogen bonds occur between very polar molecules where atoms have a high electronegativity difference. When electronegativity differences occur, the higher electronegative atom will pull the shared electrons closer to itself. With hydrogen, the highly electronegative atom pulls the electrons closer to its nucleus and further from hydrogen’s nucleus giving hydrogen a very strong positive charge. The attraction between two of these special molecules is the strongest of intermolecular attractions.
PASS Attribution
- LibreTexts PASS Chemistry Book CHEM 1500 (2).
- Question 6.E.7 from LibreTexts PASS Chemistry Book CHEM 1500 (3) is used under a CC BY-NC 4.0 license.
- Question 6.E.7 is question 10.E.1.10: Q10.1.7 from LibreTexts Chemistry 1e (OpenSTAX) (4), which is under a CC BY 4.0 license.
- Question 10.E.1.10: Q10.1.7 is question 7 from OpenStax Chemistry 2e (5), which is under a CC BY 4.0 license. Access for free at https://openstax.org/books/chemistry-2e/pages/1-introduction
References
1. OpenStax. 6.1: Intermolecular Forces. In CHEM 1500: Chemical Bonding and Organic Chemistry; LibreTexts, 2022. https://chem.libretexts.org/Courses/Thompson_Rivers_University/CHEM1500%3A_Chemical_Bonding_and_Organic_Chemistry/06%3A_Intermolecular_Forces_and_Liquids_and_Solids/6.01%3A_Intermolecular_Forces.
2. Blackstock, L.; Brewer, S.; Jensen, A. PASS Chemistry Book CHEM 1500; LibreTexts, 2023. https://chem.libretexts.org/Courses/Thompson_Rivers_University/PASS_Chemistry_Book_CHEM_1500.
3. Blackstock, L.; Brewer, S.; Jensen, A. 6.1: Question 6.E.07 PASS – Define and Explain the Types of Intermolecular Forces. In PASS Chemistry Book CHEM 1500; LibreTexts, 2023. https://chem.libretexts.org/Courses/Thompson_Rivers_University/PASS_Chemistry_Book_CHEM_1500/06%3A_Intermolecular_Forces_and_Liquids_and_Solids/6.01%3A_Question_6.E.07_PASS_-_define_and_explain_the_types_of_intermolecular_forces.
4. OpenStax. 10.E: Liquids and Solids (Exercises). In Chemistry 1e (OpenSTAX); LibreTexts, 2022. https://chem.libretexts.org/Bookshelves/General_Chemistry/Chemistry_1e_(OpenSTAX)/10%3A_Liquids_and_Solids/10.E%3A_Liquids_and_Solids_(Exercises).
5. Flowers, P.; Theopold, K.; Langley, R.; Robinson, W. R. Ch. 10 Exercises. In Chemistry 2e. OpenStax, 2019. https://openstax.org/books/chemistry-2e/pages/10-exercises.
