Presentation on theme: "Recall from Ionic Bonding… The partially positive hydrogens of the water molecules attract and pull away the negative chloride ions. The partially negative."— Presentation transcript:
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?
Intermolecular Forces inter + molecular forces = forces between molecules
Intermolecular Forces inter + molecular forces = forces between molecules Intermolecular forces are attractions between molecules. Intermolecular forces are weaker than covalent or ionic bonds.
Are caused by molecule polarity Intermolecular Forces
Determine whether a molecule is a gas, liquid, or solid at a given temperature. Think-Pair-Share How do you think intermolecular forces may determine the state of matter of a substance? Intermolecular Forces
Determine the ability of substances to dissolve one another. Intermolecular Forces
Why dont oil and water mix? Oil is nonpolar. Water is polar.
Determine the ability of substances to dissolve one another. –Like dissolves like – Polar molecules dissolve polar molecules and ionic compounds – Nonpolar molecules dissolve nonpolar molecules only Intermolecular Forces
3 Types of Intermolecular Forces Listed in order of increasing strength: London dispersion forces Dipole-dipole interactions Hydrogen bonding Note: London dispersion forces and dipole- dipole interactions are collectively called van der Waals forces.
Occur in ALL molecules The weakest of molecular interactions Caused by the motion of electrons Electrons are in constant motion. At times, more electrons can be on one side of a molecule than another. What do you think happens to the molecule when electrons do this? The strength of dispersion forces increases as the number of electrons in a molecule increases. London Dispersion Forces
The electron clouds get off- balance and attract each other slightly. London Dispersion Forces Temporary dipoles caused by the movement of electrons in a molecule.
London Dispersion Forces Temporary dipoles caused by the movement of electrons in a molecule.
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. London Dispersion Forces
At ordinary room temperature and pressure: Fluorine and Chlorine = gases Bromine = liquid Iodine = solid Why do you think this is? Explain in terms of dispersion forces.
Occur in ALL molecules- polar and nonpolar The only type of intermolecular force found in nonpolar molecules London Dispersion Forces
Dipole-Dipole Forces The + and – ends of polar molecules attract one another. Dipole-dipole interactions are similar to but much weaker than ionic bonds.
The slightly negative region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule. Dipole-Dipole Forces Do you think Dipole-Dipole Forces will occur in nonpolar molecules?
Hydrogen Bonding Strongest type of intermolecular force Hydrogen bonding always involves hydrogen Hydrogen is bonded to a very electronegative atom (oxygen, nitrogen, or fluorine) A specialized type of dipole-dipole force
A single hydrogen bond has about 5 percent of the strength of the average covalent bond. They are extremely important in determining the properties of water and biological molecules. Hydrogen Bonding
The Glue Between Molecules Dispersion force Dipole-dipole force Hydrogen bonding weakest IM force strongest IM force
Determine the strongest type of IM Force in: Dihydrogen sulfide Sulfur monoxide Dinitrogen dihydride
How do intermolecular forces influence the physical properties of substances? The diversity of physical properties among covalent compounds is mainly because of widely varying intermolecular attractions.
Properties of Substances Viscosity The ability of a substance to resist flowing
Surface Tension How difficult it is to break the surface of a liquid Properties of Substances
Evaporation A change from liquid to gas Properties of Substances
Melting Point The temperature at which a substance changes from solid to liquid or vice-versa Properties of Substances Boiling Point The temperature at which a substance changes from liquid to gas or vice-versa
How Do you Think IM Forces Affect the Following? Viscosity The ability of a substance to resist flowing Surface Tension How difficult it is to break the surface of a liquid Evaporation A change from liquid to gas Sate of Matter Boiling Point Melting Point
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 Sate of Matter High BP = STRONG IM Forces High MP = SRONG IM Forces