6.1: Question 6.E.07 PASS - define and explain the types of intermolecular forces
- Page ID
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Define the following and give an example of a molecule in which each occurs as the strongest intermolecular attraction:
a. dispersion force
b. dipole-dipole attraction
c. hydrogen bond
- Answer
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a) Dispersion Force
A dispersion force is an intermolecular attraction between temporary dipoles which form due to asymmetric electron distribution.
Example: Br2
b) Dipole-Dipole Attraction
A dipole-dipole attraction is an intermolecular attraction between two 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
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
- Strategy Map
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Step Hint 1. Identify if polarity plays a role with that type of force, this will help determine its cause. If polarity does not play a role, the type of interaction is spontaneous and non-permanent.
If polarity does play a role, the type of interaction is due to the molecule having partial charges on either end.
2. Identify the strength of the interaction. There are different types of dipole-dipole attractions. The strongest type of diploe-dipole attraction has its own name. 3. Recall which molecules the interactions occur in.
- Solution
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a) Dispersion Force
A dispersion force is an intermolecular attraction between temporary dipoles which form due to asymmetric electron distribution.
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.
Example: Br2
b) Dipole-Dipole Attraction
A dipole-dipole attraction is an intermolecular attraction between two permanent dipoles, which results from an electrostatic attraction of the positive end of one polar molecule to the negative end of another polar molecule.
For example the positive end of one polar molecule will be attracted to the negative end of another polar molecule.
Example: ICI
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.
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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Download Guided Solution as a pdf
Guided Solution Hint This is a theory type problem that asks you to define three different types of intermolecular forces and provide three molecules to exemplify each force. Question:
Define the following and give an example of a molecule in which each occurs as the strongest intermolecular attraction:
a. dispersion force
b. dipole-dipole attraction
c. hydrogen bond
See LibreText 6.1 Intermolecular Forces Recall your knowledge of polarity. 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 two molecules?
(think about magnets)
Are some attractions stronger than others?
Attraction between molecules occurs due to electrostatic attractions (when a negatively charged atom is attracted a positively charged atom).
Intermolecular forces are weaker forces that occur between molecules. There are variations of strength between the types of intermolecular forces. Dispersion forces are the weakest, dipole-dipole attractions are stronger and hydrogen bonds are a very strong type of dipole-dipole attraction.
Complete Solution:
a) Dispersion Force
A dispersion force is an intermolecular attraction between temporary dipoles which form due to asymmetric electron distribution.
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 two 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
A dispersion force is an intermolecular attraction between temporary dipoles which form due to asymmetric electron distribution.
Example: Br2
b) Dipole-Dipole Attraction
A dipole-dipole attraction is an intermolecular attraction between two permanent dipoles, which results from an electrostatic attraction of the positive end of one polar molecule to the negative end of another polar molecule.
A dipole-dipole attraction is an intermolecular attraction between two permanent diploes, 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
A dipole-dipole attraction is a force that 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
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. In the case 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 two of these molecules come into contact, they will form a very strong attraction called a hydrogen bond.
Answer
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
See LibreText 6.1 Intermolecular Forces (section 6.1.2 Dispersion Forces)
See LibreText 6.1 Intermolecular Forces (section 6.1.3 Dipole-Dipole Attractions)
See LibreText 6.1 Intermolecular Forces (section 6.1.4 Hydrogen Bonding)
Check your work!
Look at the type of molecule you have listed as the example for each intermolecular attraction and make sure it fits and that it would have that attraction as its dominant force. For teh above examples Br2 is nonpolar, ICl is a polar covalent molecule but cannot form hydrogen bonds, and HF is a polar covalent molecule that can form hydrogen bonds.
Why does this answer make chemical sense?
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. In the case 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.
(question source from page titled 10.E: Liquids and Solids (Exercises) https://chem.libretexts.org/Bookshelves/General_Chemistry/Chemistry_1e_(OpenSTAX)/10%3A_Liquids_and_Solids/10.E%3A_Liquids_and_Solids_(Exercises), shared under a CC BY 4.0 license, authored, remixed, and/or curated by OpenStax, original source https://openstax.org/books/chemistry/pages/7-exercises, Access for free at https://openstax.org/books/chemistry/pages/1-introduction)