Intermolecular Attractive Forces: Liquids and Solids Chapter 14 C2 Ch 14 ppt 1 - IMAF's.ppt C2 Ch 14 ppt 1 - IMAF's.ppt 1 1 1 1

In today’s lesson, you will learn: The different types and relative strengths of intermolecular attractive forces How to apply heat of vaporization and heat of fusion Relationship between evaporation and vapor pressure

A Molecular Comparison of Liquids and Solids

Intermolecular Forces (intramolecular attraction)

Intermolecular Forces London Dispersion Forces Weakest of all intermolecular forces. 2 nonpolar molecules. The nucleus of one molecule (or atom) attracts the electrons of the adjacent molecule (or atom). A temporary polar molecule (dipole) is formed .

Intermolecular Forces Dipole-Dipole Forces Interaction between a dipole on one molecule and a dipole on an adjacent molecule. Dipole-dipole forces exist between neutral polar molecules.

Intermolecular Forces Hydrogen Bonding A special case of dipole-dipole forces (IMAF, not bond!) Strongest of the three Van der Waals forces (Hydrogen bonding, Dipole-dipole, London forces) H directly bonded to an electronegative element (F, O, or N).

Intermolecular Forces Ion-Dipole Forces Interaction between an ion (Na+) and a dipole (water). Strongest of all intermolecular forces

Practice Draw the FCl molecule and label the positive and negative ends of the dipole. Compare with your partner.

Practice Draw the FCl molecule and label the positive and negative ends of the dipole. Compare with your partner. Use dotted lines to show the intermolecular forces. What are these IMFs called?

Practice Draw the NH3 molecule and label the positive and negative ends of the dipole. Compare with your partner.

Practice Draw the NH3 molecule and label the positive and negative ends of the dipole. Compare with your partner. Use dotted lines to show the intermolecular forces. What are these IMFs called?

Properties of Liquids Melting/freezing Change between solid and liquid phases Standard molar enthalpy of fusion (DHofus) The energy required to convert one mole of a solid at its melting point to a liquid. 6.02 kJ/mol for water Conversion factor!

Properties of Liquids Melting/freezing During a phase change, temperature does not change!

Properties of Liquids Vaporization Also called evaporation Change from a liquid to a gas. Standard molar enthalpy of vaporization (DHovap) The energy required to convert one mole of a liquid at its boiling point to a gas. 40.6 kJ/mol for water Conversion factor!

Practice Ammonia (NH3) has a melting point of -78°C and a boiling point of -33°C. Draw a heating diagram showing the melting and boiling points. Label your diagram with phases – solid, liquid, gas. (Include where there are 2 together!) Draw what the molecules would look like at each of the slanted parts.

Properties of Liquids Vapor Pressure Demonstration Pressure exerted by a substance in the gas phase. As temperature increases, vapor pressure increases. Demonstration Vapor pressure of different liquids.

Properties of Liquids Vapor Pressure Equilibrium In a closed container, liquid particles evaporate while vapor particles condense When the rate of condensation equals the rate of evaporation, the system reaches dynamic equilibrium Before reaching equilibrium: rate of evaporation > rate of condensation After reaching equilibrium: rate of evaporation = rate of condensation