H H O Slight negative charge at this end Slight positive charge at this end No overall charge Water

Atoms in a covalently bonded molecule may share electrons equally, creating a nonpolar molecule If electrons are shared unequally, a polar molecule is created Water is a polar molecule

–This makes the oxygen end of the molecule slightly negatively charged –The hydrogen end of the molecule is slightly positively charged –Water is therefore a polar molecule In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen Figure 2.9 (–) O (+) HH

The charged regions on water molecules are attracted to the oppositely charged regions on nearby molecules –This attraction forms weak bonds called hydrogen bonds Hydrogen Bonding Figure 2.10A Hydrogen bond

Like no other common substance, water exists in nature in all three physical states: Figure 2.10B –as a solid –as a liquid –as a gas

Due to hydrogen bonding, water molecules can move from a plant’s roots to its leaves Insects can walk on water due to surface tension created by cohesive water molecules Liquid Water Cohesion Figure 2.11

cohesion evaporation

It takes a lot of energy to disrupt hydrogen bonds –Therefore water is able to absorb a great deal of heat energy without a large increase in temperature –As water cools, a slight drop in temperature releases a large amount of heat Moderate Temperature

Molecules in ice are farther apart than those in liquid water Ice is less dense water Figure 2.13 Hydrogen bond ICE Hydrogen bonds are stable LIQUID WATER Hydrogen bonds constantly break and re-form

Liquid water Ice

Solutes whose charges or polarity allow them to stick to water molecules dissolve in water –They form aqueous solutions 2.14 Water is a versatile solvent Figure 2.14 Ions in solution Salt crystal Cl – Na + Cl – – –– – – Na

Cl – – – – – – – – – – – –

Salinity Salinity is a measure of the amount of salt dissolved in water –Grams of salt left behind when we evaporate 1000 g of seawater –Called parts per thousand or parts per mille

Density Density is the mass divided by the volume, or how much stuff fits in a space –Density = Mass/Volume In saltwater –Salinity ↑ Density ↑ –Temperature ↑ Density ↓ Denser stuff sits on top of less dense stuff

Light in the Ocean Transparency is the ability for of light to pass through a substance. Some wavelengths penetrate deeper Red light does not penetrate very deep. Blue light penetrates the deepest. The transparency of water is a function of the amount of stuff in the water. The more stuff suspended in the water, the less transparent the water is.

Pressure in the Ocean Pressure is a measure of force over a given area. –The weight of water is a force. Deeper = more water above you = more weight Therefore pressure increases with depth. Pressure increases at the rate of about 1 atmosphere per 10m (or 30 feet).