The Properties of Water

Remember… A molecule often consists of atoms bonded COVALENTLY! Covalent bonds occur when atoms share electrons Circle which electrons are being shared

Polarity Seen in molecules, which are often bonded covalently! Occurs when the shared electrons are attracted more strongly to one atom than to the other As a result, one end, or pole, of the molecule has a partial negative charge while the opposite side has a partial positive charge These types of molecules are POLAR

Polarity Negative Pole Positive Pole The pole with more electrons is more NEGATIVE The pole with fewer electrons is more POSITIVE Which pole is which in this diagram? Positive Pole

Hydrogen Bonds Polarity allows water molecules to be bonded together by hydrogen bonds A hydrogen bond is when a slightly positive hydrogen bonds to a slightly negative oxygen (or nitrogen or fluorine)

Solubility The partially charged ends of polar molecules attract opposite charges Because of this, water can dissolve other polar substances (like sugar and salt) Non-polar substances (like oil) don’t dissolve in water! LIKE DISSOLVES LIKE!

Properties of Water 1. Water is less dense as a solid than as a liquid When water freezes, hydrogen bonds lock water molecules into a crystal structure that has empty spaces, so ice floats! Why is this beneficial? Floating ice prevents rivers, lakes, and oceans from freezing solid, so life can exist in the water under the ice.

Properties of Water 2. Water absorbs and retains heat well It takes a lot of energy to heat or cool water Why is this beneficial? Large bodies of water can help keep temperatures on Earth from changing too fast.

Properties of Water 3. Water molecules stick to each other Hydrogen bonds hold water molecules together, so that small drops are pulled into a ball shape (aka surface tension) Cohesion is when particles of the same substance are attracted to each other Why is this beneficial? Prevents massive evaporation

Properties of Water 4. Water molecules stick to other substances Adhesion is when particles of different substances are attracted to each other Why is this beneficial?

Solutions Many substances are transported through living things as solutions of water A solution is a mixture in which one substance is evenly distributed in another substance A solute dissolves in a solvent to make a solution