Intramolecular Forces vs. Intermolecular Intramolecular Forces- chemical bonds (the forces within a single molecule) Intermolecular Forces- forces between individual molecules

IMF (intermolecular) are the reason that not everything exists as a gas.

IMF (intermolecular) are the reason that not everything exists as a gas. Solid- lots of intermolecular forces Liquid- not as many, but some still exist Gas- overcomes intermolecular forces

kinetic energy (KE) prevents molecules from interacting with each other, i.e., KE overcomes attractive intermolecular forces (IMF) What could you do to add kinetic energy? Add heat… speeds up the molecules, therefore increasing kinetic energy Reflect on last chapter (thermodynamics) what happens when heat goes from the surroundings to the system (endothermic reaction)? Think about an ice cube. Phase change (solidliquidgas)

Intermolecular Forces A substance's state of matter at a certain temperature depends on the particle’s ability to overcome intermolecular forces. Gases: kinetic energy of the particles is significantly greater than the intermolecular forces of the particles.

Intermolecular Forces Liquid: kinetic energy of the particles is greater than their intermolecular forces but not great enough for the particles to completely break free of each other.

Intermolecular Forces Solid: kinetic energy of the particles is less than the intermolecular forces of the particles.

Liquids w/high vapor pressures are called volatile (evaporate rapidly) Determined by the intermolecular forces Strong IMF= low vapor pressures (forces need high energies to escape the vapor phase) Weak IMF= high vapor pressures (doesn’t take as much energy to escape and go into the vapor phase)

SOLIDS Crystalline solids- have regular arrangements of components

Types of Crystalline Solids Ionic solid (metal + nonmetal) Molecular solid (neutral molecules) Atomic solid (components are individual atoms)

Coal, Graphite, and Diamond- all made of carbon atoms Coal, Graphite, and Diamond- all made of carbon atoms. They are atomic solids (have atoms at lattice points) The only difference is the way the Carbon is arranged.

Crystalline Solid vs. Amorphous Solid

Solutions

CA State Standard #6- Solutions are homogeneous mixtures of two or more substances. As a basis for understanding this concept: a. Students know the definitions of solute and solvent. b. Students know how to describe the dissolving process at the molecular level by using the concept of random molecular motion. c. Students know temperature, pressure, and surface area affect the dissolving process. d. Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per million, and percent composition. *e.* Students know the relationship between the molality of a solute in a solution and the solution’s depressed freezing point or elevated boiling point. *f.* Students know how molecules in a solution are separated or purified by the methods of chromatography and distillation.

Solution Homogeneous mixture- can be solid, liquid or gas Solid: Brass (alloy) is copper & zinc Liquid: Coffee Gas: the atmosphere

Solution= Solute + Solvent Solute what is being dissolved (smaller quantity present) Solvent will dissolve the solute (present in largest amount) Aqueous Solutions- water is the solvent. Water is “universal solvent”. (Note: not all liquid solutions are aqueous solutions!) Example: Country Time Lemonade What is the solute and what is the solvent?

Solvation of Ionic Substances When you dissolve an ionic substance in water, it breaks up into individual cations and anions (aqueous) Water is polar (permanent positive and negative regions due to large differences in electronegativities between H and O) The positive pole is attracted to anion and the negative pole is attracted to cation; the ionic forces are overcome and the solid dissolves (ions disperse) This is called solvation.

Aqueous or molten ionic substances are strong electrolytes This means they conduct electricity The electrical charge flows through the free cations and anions that are dispersed

Water can also dissolve nonionic substances. Ethanol is nonionic, but it has polar bonds A hydrogen bond forms between water and ethanol which overcomes IMF between individual ethanol molecules and it dissolves. The bonds within ethanol do not break (intramolecular forces). The ethanol molecules are just more attracted to water than they are to each other, thus dispersing and dissolving.

Not everything dissolves in H2O! Like dissolves like… polar substances dissolve in polar substances For a substance to dissolve, the water-water h-bonds must be broken to make a “hole” for the solute particle. They can only break if they are replace by a similar strong interaction (other polar substances). Nonpolar dissolves in nonpolar This is why you use soap + water when washing hands!

Solution Composition Saturated- contains as much solute as will dissolve at that temperature Unsaturated- more solute can still dissolve at that temperature Supersaturated- contains more solute than saturated solution will hold (must saturate at high temperature so more will dissolve) Concentrated- large amt. of solute is dissolved in solution Dilute- small amt. of solute is dissolved

Factors Affecting Rate of Dissolving 1) surface area- the greater surface area exposed to solvent will allow for faster dissolving. How can you expose more surface area?? 2) stirring- continually exposes surface to fresh solvent. 3) temperature- usually higher temperatures will allow dissolving to occur more rapidly. We brew tea in hot water for this reason!

Gases Dissolve better at LOWER temperatures. Carbonation in soda Dissolve better at HIGHER pressures

Solubility Curves

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