Chapter 17 NotesThe wonderful world of…

Water• The seemingly simple molecule—The seemingly simple molecule—

made of 1 atom of oxygen and 2 made of 1 atom of oxygen and 2 hydrogens.hydrogens.

• But oh so interesting!But oh so interesting!

Water• Water has polar bonds, and because Water has polar bonds, and because

of its bent shape, is a polar molecule.of its bent shape, is a polar molecule.

• It also undergoes Hydrogen bonding It also undergoes Hydrogen bonding due to the bond polarity between due to the bond polarity between oxygen and hydrogen.oxygen and hydrogen.

• These two factors give water some of These two factors give water some of its interesting properties!its interesting properties!

Surface Properties

• Because the Hydrogen atoms cannot Because the Hydrogen atoms cannot Hydrogen-bond to the air at its Hydrogen-bond to the air at its surface, molecules tend to be drawn surface, molecules tend to be drawn towards the body of liquid.towards the body of liquid.

Surface Properties

• This creates This creates surface tensionsurface tension—the —the inward force or pull that tends to inward force or pull that tends to minimize the surface area of a liquid.minimize the surface area of a liquid.

Though surface tension is what Though surface tension is what allows water bugs to walk on the allows water bugs to walk on the

surface of water, it does not surface of water, it does not have enough force to hold up have enough force to hold up

this guy. Sorry!this guy. Sorry!

On the hood of a car…On the hood of a car…

Surfactants

• A A surfactantsurfactant is a substance that is a substance that decreases surface tension of a liquid.decreases surface tension of a liquid.

• In water, it does this by interfering In water, it does this by interfering with the hydrogen bonding.with the hydrogen bonding.

Detergent is a good example of a surfactant.

Phase Changes

• Water boils and freezes at much Water boils and freezes at much higher temperatures than most other higher temperatures than most other substances that have similar masses. substances that have similar masses. Why? Why?

Molecular Polarity!

• Because the positive and negative side of water molecules act like tiny magnets, these forces have to be overcome in order for boiling to occur.

Phase Changes

• When water freezes, unlike most When water freezes, unlike most other substances, it becomes less other substances, it becomes less dense! It floats! Why?dense! It floats! Why?

It is very important for life on earth It is very important for life on earth that water floats when it freezes—it that water floats when it freezes—it

makes an insulating layer that makes an insulating layer that keeps the ocean from freezing and keeps the ocean from freezing and

killing everything!killing everything!

Structure of Solid Water (ice)

• What is this?

• Empty space! Just like a boat, where the average density makes it float, the empty space causes water to have a lower density as a solid than as a liquid.

Water—The Universal Solvent

• Water is called the universal solvent Water is called the universal solvent because so many different things will because so many different things will dissolve in it. How?dissolve in it. How?

Water—The Universal Solvent• Water dissolves polar and ionic Water dissolves polar and ionic

compounds because it is polar.compounds because it is polar.

• The negative side of water molecules The negative side of water molecules collide with the positive side of a polar collide with the positive side of a polar molecule (or the positive ion) and molecule (or the positive ion) and attract it, carrying it away from the attract it, carrying it away from the crystal. The same thing happens with crystal. The same thing happens with the negative side (or ion).the negative side (or ion).

Like Dissolves Like

• Nonpolar substances are able to Nonpolar substances are able to dissolve other nonpolar substances, dissolve other nonpolar substances, due to the lack of repulsive forces.due to the lack of repulsive forces.

• This leads to the saying “like This leads to the saying “like dissolves like.”dissolves like.”

Electrolytes• Any ionic compound will conduct Any ionic compound will conduct

electricity when dissolved in water. electricity when dissolved in water. Compounds that do so are called Compounds that do so are called electrolyteselectrolytes..

• Non-electrolytesNon-electrolytes—like —like sugar—will dissolve sugar—will dissolve but but do not conduct do not conduct electricity.electricity.

Heterogeneous Aqueous Systems

• There are two types of There are two types of heterogeneous aqueous systems—heterogeneous aqueous systems—colloids and suspensions.colloids and suspensions.

Suspensions

• Mixtures where particles settle out Mixtures where particles settle out upon standing are called upon standing are called suspensionssuspensions..

• They differ from solutions (which are They differ from solutions (which are homogeneous) because their homogeneous) because their particles are much larger.particles are much larger.

Colloids• A A colloidcolloid is a mixture with is a mixture with

particles intermediate in size particles intermediate in size between a solution and a between a solution and a suspension.suspension.

• They have properties that are They have properties that are different than both. For example, different than both. For example, the particles in a colloid exhibit the particles in a colloid exhibit Brownian motionBrownian motion..

Brownian Motion

• The random drifting of particles suspended in a fluid.

• This occurs when the particles are small enough that the effects of gravity are smaller than the interactions with other particles, resulting in a scattering of particles and no settling.

How can you tell what it is?

• A colloid can be discerned due to the A colloid can be discerned due to the Tyndall effectTyndall effect—light scattering by —light scattering by particles in a colloid or particles in a particles in a colloid or particles in a fine suspension. fine suspension.