Chemistry Discussion 13: Intermolecular Forces

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What type of intermolecular attractions causes gas phase molecules to condense into liquids and solids?

Nuclear forces

Electrostatic forces

Covalent bonds

Intermolecular attractions (correct)

If a liquid has a high boiling point, it has strong intermolecular attractions.

True

How does molecular dipole moment correlate with boiling point?

Compounds with larger dipoles have a greater boiling point due to stronger intermolecular attractions.

What are London dispersion forces?

Attractive forces important in nonpolar molecules due to temporary dipole-induced dipoles. Signup and view all the answers

Do molecular weights correlate with freezing points for monatomic substances?

Yes Signup and view all the answers

If a liquid has a low freezing point, it has strong intermolecular attractions.

False Signup and view all the answers

Based on polarity, would CH3F have a higher or lower boiling point than CH3Cl?

Higher boiling point. Signup and view all the answers

Based on dispersion forces alone, would CH3F have a higher or lower boiling point than CH3Cl?

Lower boiling point. Signup and view all the answers

Which interactions are more important for determining relative boiling points: dispersion or dipole interactions?

Dispersion interactions. Signup and view all the answers

What is hydrogen bonding?

A strong intermolecular attraction occurring between hydrogen and F, O, or N. Signup and view all the answers

Rank H2O, H2S, and H2Se in order of increasing dispersion interactions.

H2O < H2S < H2Se Signup and view all the answers

Rank NH3, PH3, and AsH3 in order of increasing dispersion interactions.

NH3 < PH3 < AsH3 Signup and view all the answers

For CH4, the polar/nonpolar nature is ______.

Nonpolar Signup and view all the answers

For CH3Cl, the polar/nonpolar nature is ______.

Polar Signup and view all the answers

For CH3OH, the polar/nonpolar nature is ______.

Polar Signup and view all the answers

Predict the order of freezing and boiling points for CH4, CH3Cl, and CH3OH from lowest to highest.

CH4 < CH3Cl < CH3OH Signup and view all the answers

What does a phase diagram show?

A graph mapping conditions where a substance is found as solid, liquid, or gas. Signup and view all the answers

Identify where water is a gas, liquid, and solid in a phase diagram.

Gas: high T, low P; Liquid: low T, mid P; Solid: low T, high P. Signup and view all the answers

If starting at point A and increasing temperature, what phases will you observe?

Solid to Liquid to Gas. Signup and view all the answers

Study Notes

Intermolecular Forces

Intermolecular attractions lead to condensation from gas to liquid/solid states.
Key attractions involve dipole moments in polar covalent molecules.
Bond dipole examples: H → F and S → H.

Electronegativity Values

Electronegativity scale: F (4.0), O (3.5), Cl (3.0), C and S (2.5), H (2.1), Si (1.8).

Boiling Points of Molecules

Comparative boiling points (°C): H2O (100), HF (20), CH3Cl (-24), H2S (-60), HCl (-85), CH4 (-161).
High boiling points indicate strong intermolecular attractions; low points indicate weak attractions.

Molecular Dipole Moments and Boiling Points

Dipole strength influences boiling points: CH4 < HCl < HF / H2S < H2O.
Higher dipole strength correlates with greater boiling points among nonpolar molecular compounds.

London Dispersion Forces

Significant for nonpolar molecules; arise from temporary dipole-induced dipoles.
Relevant data: Ne (-249°C, MW 20.1797 g/mol), He (-270°C, MW 4.003 g/mol), CO2 (-56°C, MW 44.01 g/mol), CH4 (-183°C, MW 16.04 g/mol), H2 (-259°C, MW 2.016).

Correlation of Molecular Properties

Monatomic substances show correlation between freezing point, molecular weight, and electron count.
Nonpolar polyatomic species display similar correlations.

Freezing and Intermolecular Strength

Low freezing points indicate weak intermolecular attractions.

Comparing Boiling Points of CH3F and CH3Cl

CH3F is expected to have a higher boiling point than CH3Cl due to greater polarity (higher EN for F).
Ultimately determined by stronger dipole-dipole attractions in CH3F versus larger dispersion forces in CH3Cl.

Relative Importance of Interactions in CH3F and CH3Cl

Actual boiling points: CH3F (-78°C) vs. CH3Cl (-24°C); CH3Cl has stronger dispersion interactions, leading to a higher boiling point.

Hydrogen Bonding

Hydrogen bonds occur with H atoms bonded to F, O, or N; they are stronger than typical dipole-dipole and dispersion interactions but weaker than covalent bonds.
Notable boiling points include: H2O (100°C), H2S (-60°C), NH3 (-33°C).

Ranking Dihydrides and Trihydrides

Dihydrides: Predicted order based on dispersion interactions is H2O < H2S < H2Se; H2O ranks higher due to hydrogen bonding.
Trihydrides: Order should be NH3 < PH3 < AsH3; NH3 is also elevated due to hydrogen bonding.

Intermolecular Interactions by Molecule

CH4: Nonpolar, exhibits only dispersion forces.
CH3Cl: Polar, exhibits both dispersion and dipole-dipole forces.
CH3OH: Polar, exhibits dipole-dipole, dispersion, and hydrogen bonding interactions.

Freezing and Boiling Point Order

Expected order: CH4 < CH3Cl < CH3OH, driven by the presence of hydrogen bonding in CH3OH.

Phase Diagrams

Phase diagrams illustrate conditions (temperature and pressure) where substances exist as solid, liquid, or gas.
Curves delineate boundaries between stable phases.

Water’s Phase Regions

Solid phase: low temperature, high pressure.
Liquid phase: moderate temperature and pressure.
Gas phase: high temperature and low pressure.

Phase Transitions of Water

As temperature increases from a solid, water first transitions to liquid, then to gas.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz focuses on the concepts related to intermolecular forces, including bond dipoles and electronegativity of various elements. It also examines the boiling points of specific molecules as a result of these forces. Test your understanding and grasp these foundational chemistry principles.