Transcript Slide 1
Notes: 13.2 • OBJECTIVES: Students will be able to (SWBAT) 1. Predict the type of intermolecular forces that will affect molecules • QUESTIONS TO PONDER: 1. What is the difference between intermolecular and intramolecular attractions? 2. What are some examples of different type of IMFs? 3. What factors affect the types of IMFs molecules experience? 4. What are some properties affected by IMFs? Forces of Attraction (13.2) • Intermolecular forces (IMF) – the forces between molecules or particles. • Intramolecular forces – the forces within molecules or particles. Intramolecular force Intermolecular force Intramolecular Forces • Intramolecular forces are the forces within the compound itself the bonds between atoms in a compound or molecule – Ionic – Covalent – Metallic ionic metallic covalent 4 Types of Intermolecular Forces 1. 2. 3. 4. dispersion or London Forces (weakest) Dipole-induced interactions (stronger) Dipole-dipole interactions (even stronger) Hydrogen-bonding (strongest) London Dispersion Forces • dispersion or London Forces (weakest) – between 2 or more nonpolar molecules – When the electron cloud of one nonpolar molecule nears another nonpolar molecule, electrons will temporarily shift or disperse – When close enough, the dispersed electrons to one end will be more negative and attract to the more positive side of another nonpolar molecule (side with less disperse electrons) London Dispersion Forces Dipole-dipole interactions • Dipole-dipole (stronger) – between 2 or more polar molecules – Positive end of one molecule is attracted to the negative end of another molecule Dipole-induced interactions • When a polar molecule causes a nonpolar molecule to temporarily have a dipole by dispersing its electron cloud • Attraction strength is between dispersion and dipole-dipole POLAR NONPOLAR TEMPORARY DIPOLE Hydrogen Bonds (H-bonds) • Hydrogen bonds – Type of dipole-dipole force – Occurs when molecules have H attached to F, O, or N (high EN) • Ex H2O – Strongest attraction out of the intermolecular forces Factors that affect IMF Strength 1. Type of IMF (London, dipole-dipole, H-bond) 2. Molecular Weight (big vs small, long vs short) Hydrocarbons • Hydrocarbons are molecules that contain mostly C’s and H’s (sometimes O’s and N’s and others) • They can be very big because C can link together in a long chain • They can form rings as well • Hydrocarbons that are only C’s and H’s and are symmetrical are generally nonpolar Straight-chained hydrocarbon Ringed hydrocarbon Nonpolar hydrocarbon – more “even” areas Polar hydrocarbon – an area that is more positive or negative than the rest Molecular Weight • Larger mass stronger interactions between atoms more “cloud” to move around – CH4 is a gas at room temperature – C8H18 is a liquid at room temperature Most likely a gas at room temperature Most likely a liquid or solid at room temperature Boiling and Melting Point • Melting point (mp) when a solid becomes liquid • Boiling point (bp) when a liquid becomes a gas • Stronger interactions harder to pull apart more likely a liquid or a solid • Higher mp or bp more heat/energy to pull apart molecules because stronger IMFs – Polar: higher mp/bp than nonpolar – Heavier nonpolar: higher mp/bp than lighter nonpolar Bond type Covalent Nonpolar Small Ionic Polar Forces: weakest to strongest london Dipoledipole Hydrogen bond intramolecular