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Intermolecular Forces and Liquids and Solids

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Intermolecular Forces and Liquids and Solids Intermolecular Forces and Liquids and Solids 1 Intermolecular Forces and Liquids and Solids y Kinetic Molecular Theory of Liquids and Solids (12.1) y Intermolecular Forces (12.2) y Properties of Liquids (12.3) y Crystal Structures (12.4) y Bonding in Solids (12.5) y Phase Changes (12.6) y Phase Diagrams (12.7) 12.1 The Kinetic Molecular Theory of Liquids and Solids y How are solids and liquids modeled on the particle-level? y How does this help explain macroscopic properties of solids and liquids? Intermolecular Forces and Liquids and Solids H2O(g) H2O(l) H2O(s) Figure 1.2, p. 4 12.1 The Kinetic Molecular Theory of Liquids and Solids Table 12.1, p. 403 12.1 The Kinetic Molecular Theory of Liquids and Solids y Does the molecular structure of the substance on the particle level affect function or properties on the macroscopic level? We finally connect between the abstract (the bonding and structure of substances) to the observed (the function and properties of substances) 12.2 Intermolecular Forces y What are intramolecular forces: ◦ Forces that hold atoms together in a molecule y What are intermolecular forces: ◦ attractive forces between molecules y How do we model these? Intermolecular force (between molecules) ◦ Let’s consider water: Intramolecular force (covalent bonds in molecules) 12.2 Intermolecular Forces Intermolecular vs Intramolecular •41 kJ to vaporize 1 mole of water (inter) • 930 kJ to break all O‐H bonds in 1 mole of water (intra) Intermolecular force Generally, intermolecular (between molecules) forces are much weaker than intramolecular forces. Intramolecular force (covalent bonds in molecules) 12.2 Intermolecular Forces “Measure” of intermolecular force: boiling point melting point Δ Δ Δ Hvap Hfus Hsub Intermolecular force (between molecules) Intramolecular force (covalent bonds in molecules) 12.2 Intermolecular Forces Focus on pure substances first: y How do we model pure substances? y How are intermolecular forces separated into categories? We will use structure and size to assist in approximating intermolecular forces and connect this to physical properties 12.2 Intermolecular Forces y Can all substances be liquefied? y Why? y Dispersion Forces: ◦ Attractive forces that arise as a result of a temporary dipole induced in atoms or molecules IMF – Substances Pure Figure 12.5, p. 406 12.2 Intermolecular Forces y Polarizability: ◦ The ease with which the electron distribution in the atom or molecule can be distorted y Polarizability increases with greater number of electrons or more diffuse electron cloud Dispersion forces usually increase with molar mass. As dispersion forces increase, intermolecular forces increase. IMF – Substances Pure Therefore, it takes more energy to overcome these and the melting points and boiling points increase 12.2 Intermolecular Forces y What are the states of the halogens under standard conditions? IMF – Substances Pure Table 12.2, p. 406 12.2 Intermolecular Forces y Permanent vs. induced dipole moments y Dipole Forces: ◦ Attractive forces between polar molecules IMF – Substances Pure Figure 12.1, p. 404 12.2 Intermolecular Forces y What is the trend of boiling points of HI, HBr, HCl and HF? 350 300 250 200 150 IMF – Substances Pure 100 Boiling point (K) 50 0 HF HCl HBr HI 12.2 Intermolecular Forces y Specific type of dipole force y Hydrogen bonding (IMF – not covalent bond): ◦ Special type of dipole-dipole interaction between the hydrogen atom in a polar bond, such as N-H, O-H or F-H and an electronegative O, N, or F atom. IMF – Substances Pure Figure, p. 409 12.2 Intermolecular Forces IMF – Substances Pure Figure 12.7, p. 405 12.2 Intermolecular Forces Hydrogen bonding Greater IMF Higher boiling pt Decreasing molar mass Decreasing boiling point No hydrogen bonding IMF – Substances Pure Figure 12.6, p. 408 12.2 Intermolecular Forces Dispersion forces Dipole forces Hydrogen bonding IMF – Substances Pure 12.2 Intermolecular Forces y Using IMF with pure substances: Approximating relative melting or boiling points 1. Determine the intermolecular forces of the substances (usually comparing between two different pure substances) 2. Consider the number of intermolecular forces: If they are different, then the substance with the higher number of intermolecular forces has the higher boiling point If they are the same, then the substance with the IMF – Substances Pure higher number of electrons has the higher boiling point 12.2 Intermolecular Forces y Using IMF with pure substances: Which has the higher boiling point? 1. Determine the IMF 2. Consider the number of intermolecular forces: If they are different, then the substance with the higher number of intermolecular forces has the higher boiling point If they are the same, then the substance with the higher number of electrons has the higher boiling point Boiling Substance Point, oC IMF – Substances Pure C2H4 -104 NF3 71 NCl3 C2H4 States at room temperature? 12.2 Intermolecular Forces y Using IMF with pure substances: Which has the higher boiling point? 1. Determine the IMF 2. Consider the number of intermolecular forces: If they are different, then the substance with the higher number of intermolecular forces has the higher boiling point If they are the same, then the substance with the higher number of electrons has the higher boiling point Boiling H H H H H H Substance Point, oC IMF – Substances Pure H C C H C H C C O H O butanol 157 H H H H methanol 65 butanol methanol States at room temperature? 12.2 Intermolecular Forces IMF – Mixtures Figure 12.7, p. 408 12.2 Intermolecular Forces Now focus on mixtures: y How do we model mixtures? y How do the intermolecular forces and sizes of molecules affect solubility? We will use structure and size to assist in IMF – Mixtures approximating intermolecular forces and connect this to physical properties Think about this like a “substitution” 12.2 Intermolecular Forces IMF – Mixtures Margin Figure, p. 409 12.2 Intermolecular Forces y Using IMF with mixtures: Approximating solubility 1. Determine the intermolecular forces of the substances (usually considering the solubility of two pure substances) 2. Determine the relative size of the two molecules (same or different) If both (IMF and size) are the same, then we would IMF – Mixtures approximate that the substances are soluble If both (IMF and size) are different, then we could approximate that the substances are insoluble If one (IMF or size) are the same, then we would approximate that the substances are partially soluble 12.2 Intermolecular Forces y Using IMF with mixtures: What is the solubility of the two substances? 1. Determine the IMF 2. Determine the relative size of the two molecules (same or different) If both (IMF and size) are the same, then the substances are soluble If both (IMF and size) are different, then the substances are insoluble If one (IMF or size) are the same, then the substances are partially soluble IMF – Mixtures H H C H Solubility (g in 100g) H O Infinitely (miscible) methanol water What does this look like? 12.2 Intermolecular Forces y Using IMF with mixtures: What is the solubility of the two substances? 1. Determine the IMF 2. Determine the relative size of the two molecules (same or different) If both (IMF and size) are the same, then the substances are soluble If both (IMF and size) are different, then the substances are insoluble If one (IMF or size) are the same, then the substances are partially soluble IMF – Mixtures H H H H H C C H Solubility (g in 100g) C C O 8.88 H H H H butanol water What does this look like? 12.2 Intermolecular Forces Alcohol Solubility (g in 100g H2O) Infinitely (miscible) 8.88 2.73 IMF – Mixtures 0.602 0.174 What do these look like? 12.2 Intermolecular Forces y Using IMF with mixtures: Determining IMF that exist between the substances: ◦ Dispersion forces (or induced dipole-induced dipole) between all substances in a solution. ◦ A nonpolar and a polar substance would have induced dipole-dipole forces ◦ A polar and a polar substance would have dipole-dipole forces IMF – Mixtures ◦ A ionic and a nonpolar substance would have ion-induced dipole forces ◦ A ionic and a polar substance would have ion-dipole forces 12.2 Intermolecular Forces y Using IMF with mixtures: What are the IMF between the two substances? Determine the IMF x Dispersion forces (or induced dipole-induced dipole) between all substances in a solution. x A nonpolar and a polar substance would have induced dipole-dipole forces x A polar and a polar substance would have dipole-dipole forces x A ionic and a nonpolar substance would have ion-induced dipole forces x A ionic and a polar substance would have ion-dipole forces IMF – Mixtures H H C H H O methanol water dipole-dipole forces dispersion forces 12.2 Intermolecular Forces y Using IMF with mixtures: What are the IMF between the two substances? Determine the IMF x Dispersion forces (or induced dipole-induced dipole) between all substances in a solution. x A nonpolar and a polar substance would have induced dipole-dipole forces x A polar and a polar substance would have dipole-dipole forces x A ionic and a nonpolar substance would have ion-induced dipole forces x A ionic and a polar substance would have ion-dipole forces IMF – Mixtures Salt, NaCl water ion-dipole forces dispersion forces Which molecule does not have the intermolecular force of hydrogen bonding as a pure I II III substance? (A) Only I(B)Iand II (C) I and III (D) II and III Chapter 12 –Chapter Practice 12.3 Properties of Liquids y How is structure related to other properties of liquids (surface tension, viscosity)? y What is surface tension? ◦ The amount of energy required to stretch or increase the surface of a liquid by a unit area ◦ Would you expect higher intermolecular forces, higher surface tension Figure 12.8, p.
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