Properties of Water

The Unique Properties of Water Water is a very unusual substance It has many properties that differ from those of most other familiar substances It is H20, meaning every water molecule has 1 atom of Oxygen and 2 atoms of Hydrogen

Specific Heat Compared to other substances, water requires a lot of heat to increase its temperature (Think of a hot sandy beach, but cool ocean water) Specific heat: the amount of heat needed to raise the temperature of a certain substance by 1 degree Celsius Water has a high specific heat

Polar Water is a polar molecule A polar molecule is a molecule that has electrically charged areas Hydrogen + Oxygen – The positive hydrogen ends of one water molecule attract the negative oxygen ends of nearby water molecules. As a result, the water molecules tend to stick together

Because it’s Polar… Many of water’s unusual properties occur because of the attraction among polar water molecules The properties of water include capillary action, surface tension, the ability to dissolve many substances, and high specific heat

Solution vs. Solvent Solution – a mixture that forms when one substance dissolves another Solvent – the substance that does the dissolving In most cases, the solvent is water AKA: Universal Solvent

Universal Solvent Water is called the “universal solvent” because it dissolves almost anything! The charged ends of the polar water molecule attract the molecules of other polar substances

Cohesion vs. Adhesion Cohesion - The tendency of water molecules to form weak bonds and stick together Adhesion - The tendency of water to stick to other substances (besides itself)

Surface Tension Surface Tension: the tightness across the surface of water that is caused by the polar molecules pulling on one another * caused by cohesion This explains how you can skip a rock or spiders can walk across water’s surface

Surface Tension The Basilisk lizard makes use of the high surface tension of water to accomplish the incredible feat of walking on water's surface.  It can't actually walk on water; rather, it runs on water, moving its feet before they break through the surface.  Take a look: Miracle Lizard

Capillary Action Capillary action: the combined force of attraction among water molecules and with the molecules of surrounding materials * caused by adhesion Allows water to stick to the inside of a straw, move through materials with pores, and cling to fibers of materials like cloth and paper

Buoyancy Buoyancy – the ability to float (this is how boats float!) Water and other fluids exert an upward force called the buoyant force that acts on a submerged object Buoyant Force – acts in the direction opposite to the force of gravity, so it makes an object feel lighter - an object will sink if its weight is greater than the buoyant force

Hydrophobic vs. Hydrophilic Hydrophobic – molecules that are repelled by water -literally means “fear of water” -usually non-polar, so they are not attracted to water’s charges -example: oils Hydrophilic - molecules that are attracted to water - literally means “water loving” -typically polar molecules that are charged -example: salt or anything that dissolves in water

Amphipathic Molecule Amphipathic Molecule - a molecule that contains both polar and nonpolar regions Very important in the human body

Changing of States Water is the only substance on Earth that commonly exists in all of these different states

Density of Water D= m/v In water's liquid form, hydrogen bonding pulls water molecules together.  As a result, liquid water has a relatively compact, dense structure.  Liquid Water and Hydrogen Bonding As water freezes into ice, the molecules become frozen in place and begin to arrange themselves in a rigid lattice structure Ice and Hydrogen Bonding

The solid ice crystal actually has large holes in it.  There are fewer molecules in a given volume of ice than in liquid water! In other words, ice is less dense than liquid water and will float on the surface of the liquid! HOW CRAZY IS THAT!?!

Lattice Structure of Ice Water Check out how the bonding is different for the solid and the liquids… Lattice Structure of Ice Water FYI…The normal pattern for most compounds is that as the temperature of the liquid increases, the density decreases as the molecules spread out from each other. As the temperature decreases, the density increases as the molecules become more closely packed. This pattern does not hold true for ice as the exact opposite occurs.