CHEM 1F92 Lecture Notes - Lecture 1: The Strongest, Electronegativity, Hydrogen Bond

49 views1 pages

aquamarinebadger428

2 Mar 2018

School

Brock University

Department

Chemistry

Course

CHEM 1F92

Professor

Theocharis C Stamatatos

For unlimited access to Class Notes, a Class+ subscription is required.

Document Summary

Intramolecular forces - chemical bonding, forces that hold atoms together in a molecule. Generally, intermolecular forces are much weaker than intramolecular forces. The strength of interactions depend on both the charge and the size of the ion. Ion-dipole forces are weaker than the ion-ion forces. Force of (na+- h2o) < force of (mg2+- h2o) The smaller the ion, and the larger its charge, the stronger the ion-dipole interaction. The positively charged end of a polar molecule such as h2o is attracted to negative ions and the negatively charged end of the molecule is attracted to positive ions. The orientation of dipoles depend on the charge on the ion. Heat of hydration is directly proportional to the strength of the ion-dipole interaction. The strongest ion-dipole force will have the highest heat of hydration. Hydrogen bonding is a special type of dipole dipole force.

Related Questions

* Circle the intermolecular force(s) that is/are present in each of the following species. [Hint: there may be more than one correct answer.]

Ar (hydrogen bonding, dipole-dipole forces, dispersion forces)

CH4 (hydrogen bonding, dipole-dipole forces, dispersion forces)

HBr (hydrogen bonding, dipole-dipole forces, dispersion forces)

HF (hydrogen bonding, dipole-dipole forces, dispersion forces)

CHCl3 (hydrogen bonding, dipole-dipole forces, dispersion forces)

* For the following pairs of atoms/molecules, circle the species that has the higher boiling point.

Ne or Xe

Cl2 or F2

HBr or HF

HCl or HI

H2O or H2S

* Phase changes always associate with change of enthalpy. For the following situations, name the phase

transition and indicate whether the process is exothermic or endothermic.

(a) Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide.

Answer:

(b) Water vapor turns to liquid water.

Answer:

(d) Iodine vapor turns to solid iodine.

Answer:

(e) Liquid helium turns to helium gas.

Answer:

* True or false

1. Intermolecular forces are stronger than ionic and covalent bonds. Answer:

2. For molecules with similar size and molar mass, those with higher polarity would have higher boiling

point. Answer:

3. Ion-dipole forces exist between ionic potassium bromide and polar water.

Answer:

4. Dispersion forces exist between argon and helium. Answer:

5. Instantaneous dipoles exist in all molecules and atoms. Answer:

6. The strength of dispersion forces depends on the molar mass but the shape of the molecules have no effect on dispersion forces. Answer:

7. Ice has a higher density than water because ice has an ordered cagelike structure. Answer:

8. Liquids with weaker intermolecular interactions have lower viscosity. Answer:

9. Viscosity decreases with increasing temperature. Answer:

10. For any molecules, the heat of vaporization is always lower than the heat of fusion because it takes more energy to make molecules to move past one another in a solid lattice. Answer:

The following table presents the solubilities of several gases in water at 25 °C under a total pressure of gas and water vapor of 1 atm. (a) What volume of CH₄(g) under standard conditions of temperature and pressure is contained in 4.0 L of a saturated solution at 25 °C? (b) Explain the variation in solubility among the hydrocarbons listed (the first three compounds), based on their molecular structures and intermolecular forces. (c) Compare the solubilities of O₂, N₂, and NO, and account for the variations based on molecular structures and intermolecular forces. (d) Account for the much larger values observed for H₂S and SO₂ as compared with the other gases listed. (e) Find several pairs of substances with the same or nearly the same molecular masses (for example, C₂H₄ and N₂), and use intermolecular interactions to explain the differences in their solubilities.

The corresponding volume is

b) All three molecules are nonpolar and form very weak interactions with the water molecules. The solubility of ethane is higher that the solubility of methane as ethane is more massive molecule and forms stronger dispersion forces with the water molecule. Ethene is the most soluble gas as the C atoms in ethene are planar, sp² hybridized, and there are π electrons in the orbitals perpendicular to the carbon atoms. π electrons are less tightly held by the nucleus than σ electrons, allowing the dipole of water molecule to disturb the electron density more easily, leading to stronger dipole-induced dipole interactions.

c) The molecular weight is similar for three gases. O₂ and N₂ are nonpolar gases, but more water molecules surround O₂ as it is larger molecule. The O–O bond (double bond) is longer than N–N bond (triple bond). The water attracts nonpolar gases through the weak dipole-induced dipole interactions. NO is the most soluble gas as it has polar bond and the overall molecule is polar as it is linear structure. Water dissolves it via stronger dipole-dipole interactions.

d) H₂S is capable to form weak hydrogen bonds with the water molecules, and these interactions are much stronger than dipole-dipole and dispersion forces. SO₂ is even more soluble in water as it reacts with the water forming H₂SO₃. The very high values for the solubility of gas are the sign that the gas chemically reacts with the solvent.

d) N₂ and CH₄. Solubility of N₂ is lower as N₂ is smaller molecule than CH₄ and less hydrated.

NO and C₂H₆ have similar water solubility. NO is more soluble than ethane and form dipole-dipole interactions, but the dispersion forces of ethane and water are stronger than dispersion forces between NO and water as ethane is larger, more polarizable molecule. The sum of all intermolecular interactions is similar for these two gases, leading to the similar water solubility.

NO and O₂. NO is more soluble as it is polar molecule and form stronger intermolecular forces with polar solvent molecules compared to nonpolar O₂ molecule.

turquoisecattle345

CHEM 1F92 Lecture Notes - Lecture 1: The Strongest, Electronegativity, Hydrogen Bond

Document Summary

Get access

Related textbook solutions

Chemistry: Structure and Properties

Basic Chemistry

Principles of Chemistry Molecular Approach

Principles of Chemistry Molecular Approach

Chemistry: Structure and Properties

Chemistry: A Molecular Approach

Chemistry: A Molecular Approach

Principles of Chemistry: A Molecular Approach

Chemistry: The Central Science

Related Documents

CHEM 1F92 Lecture Notes - Lecture 2: Boiling Point, Dipole, Intermolecular Force

CHEM 1F92 Lecture Notes - Lecture 37: Strath, Hydrogen Bond

CHEM 1F92 Lecture Notes - Lecture 1: Valence Bond Theory, Intramolecular Force, Intermolecular Force

Related Questions