Presentation on theme: "Recall from Ionic Bonding…"— Presentation transcript:
1 Recall from Ionic Bonding… The partially positive hydrogens of the water molecules attract and pull away the negative chloride ions.The partially negative oxygens of the water molecules attract and pull away the positive sodium ions.Big Question: For one substance to dissolve another, what is required of both substances?
3 Intermolecular Forces forces between moleculesIntermolecular forces are attractions between molecules.Intermolecular forces are weaker than covalent or ionic bonds.
4 Intermolecular Forces Are caused by molecule polarity
5 Intermolecular Forces Determine whether a molecule is a gas, liquid, or solid at a given temperature.Think and ShareHow do you think intermolecular forces may determine the state of matter of a substance?
6 Why don’t oil and water mix? Oil is nonpolar.Water is polar.
7 IMF’s and SolubilityDetermine the ability of substances to dissolve one another.“Like dissolves like”Polar molecules dissolve polar molecules and ionic compoundsNonpolar molecules dissolve nonpolar molecules only
8 How do intermolecular forces influence the other physical properties of substances? The diversity of physical properties among covalent compounds is mainly because of widely varying intermolecular attractions.
9 Properties of Substances ViscosityThe ability of a substance to resist flowing
10 Properties of Substances Surface Tension How difficult it is to break the surface of a liquid
11 Properties of Substances Evaporation and Vapor Pressure A change from liquid to gas
12 Properties of Substances Melting PointThe temperature at which a substance changes from solid to liquid or vice-versaBoiling PointThe temperature at which a substance changes from liquid to gas or vice-versa
13 3 Types of Intermolecular Forces Listed in order of increasing strength:London dispersion forces [low strength[Dipole-dipole interactionsHydrogen bonding [highest strength]van der Waals forces=London dispersion forces + dipole-dipole interactionsDipole=separation of + and – chargea molecule with a + end and a - end
14 London Dispersion Forces Occur in ALL molecules (non-polar and polar)The weakest of molecular interactionsCaused by the motion of electronsElectrons are in constant motion. At times, more electrons can temporarily be on one side of a molecule than another.What do you think happens to the molecule when more electrons are on one side than another?
15 London Dispersion Forces Temporary dipoles caused by the movement of electrons in a molecule.
17 London Dispersion Forces A single dispersion force is very weak by itself.However, when millions and millions of dispersion forces happen in a substance the force dispersion force is a significant intermolecular force.The strength of dispersion forces increases as the number of electrons in a molecule increases.
18 At ordinary room temperature and pressure: Fluorine and Chlorine = gases Bromine = liquid Iodine = solidWhy do you think this is? Explain in terms of dispersion forces.
19 London Dispersion Forces Occur in ALL molecules- polar and nonpolarThe only type of intermolecular force found in nonpolar molecules
20 Dipole-Dipole ForcesThe + and – ends of polar molecules attract one another.Dipole-dipole interactions are similar to but much weaker than ionic bonds.
21 Do you think Dipole-Dipole Forces will occur in nonpolar molecules? The slightly negative region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule.Do you think Dipole-Dipole Forces will occur in nonpolar molecules?
22 Hydrogen Bonding Strongest type of intermolecular force A specialized type of dipole-dipole forceStrongest type of intermolecular forceHydrogen bonding always involves hydrogenHydrogen is bonded to a very electronegative atom.Hydrogen bonding occurs ONLY when a H isbonded directly to oxygen, nitrogen, or fluorine
23 Hydrogen BondingA single hydrogen bond has about 5 percent of the strength of the average covalent bond.However, lots of hydrogen bonds add up to be of significant strength.Hydrogen bonds are extremely important in determining the properties of water and biological molecules.
24 The “Glue” Between Molecules Dispersion forceDipole-dipole forceHydrogen bondingweakestIM forceCopy this slide on the back of Do NowstrongestIM force
25 Questions (Think-Pair-Share) What causes dispersion forces? Which types of molecules have dispersion forces? (nonpolar or polar) What types of molecules have dipole-dipole forces?
26 Determine the strongest type of IM Force in: Dihydrogen sulfide Sulfur monoxide Dinitrogen dihydride Carbon tetrachloride
27 How Do you Think IM Forces Affect the Following? ViscosityThe ability of a substance to resist flowingSurface TensionHow difficult it is to break the surface of a liquidEvaporationA change from liquid to gasSate of MatterBoiling PointMelting Point
28 How Do you Think IM Forces Affect the Following? Viscosity high viscosity = STRONG IM Forces Surface Tension high surface tension = STRONG IM Forces Evaporation fast evaporation rates = WEAK IM Forces State of Matter High BP = STRONG IM Forces High MP = SRONG IM Forces