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Attractions Between Molecules

Attractions Between Molecules. Homework Review. 3.7 Predict the shapes of the following molecules and indicate whether they are polar covalent or nonpolar covalent. a) I 2 b) HCl c) PH 3 d) SiCl 4 e) CS 2. Homework Review. 3.8

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Attractions Between Molecules

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  1. Attractions Between Molecules

  2. Homework Review • 3.7 Predict the shapes of the following molecules and indicate whether they are polar covalent or nonpolar covalent. a) I2 b) HCl c) PH3 d) SiCl4 e) CS2

  3. Homework Review • 3.8 Figure 3-9 on p. 129 shows how a thin stream of water is attracted by a charged rod. Which of the substances listed in question 3.7, when in the liquid state, would behave in a manner similar to that of water?

  4. Van der Waals Forces • Attractions between molecules • Dispersion Forces – the weak intermolecular forces of attractions between nonpolar molecules. P+ P+ dispersion forces • Very weak e- e-

  5. Dispersion Forces Increase as protons and electrons increase CH4CH4 weaker C3H8C3H8 stronger

  6. Dipole – Dipole Forces • Between polar molecules + H – Cl-+ H – Cl- Dipole attraction

  7. Hydrogen Bonds • Very strong dipole attraction between molecules • Need hydrogen and either nitrogen, oxygen or flourine hydrogen bond + H – N - + H – N -

  8. Which is Stronger? B (hydrogen bond) A or B ? Answer: A (covalent bond) A (covalent bond) Which will have a lower melting point? Water NaCl Answer: Water B or C ? Answer: C(ionic bond) + Na – Cl- C (ionic bond)

  9. Properties of Covalent Substances • Melting point  low • Conductivity  no • Hardness  soft *except for network solids • “like dissolves like” *polar dissolves polar *nonpolar dissolves nonpolar Youtube Video

  10. Attractions Summary Covalent lower attractions nonpolar – symmetrical H – H H – H polar – asymmetrical + H – Br -+H – Br - hydrogen bond H – F H – F ionic + Na – Cl- network solids higher attractions diamonds, SiO2

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