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2 Polar Covalent vs. Nonpolar Covalent Polar covalent- which means 2 different nonmetals (ex. water or ammonia) (have opposite charges on molecule b/c electrons are more attracted to oxygen) Nonpolar Covalent- means 2 of the same nonmetals (ex. Oxygen or nitrogen gas) and they do not have opposite charges and share electrons equally.

3 100 o C - steam

4 Water consists of an oxygen atom bound to two hydrogen atoms by two single polar covalent bonds. – Oxygen has unpaired & paired electrons which gives it a slightly negative charge while Hydrogen has no unpaired electrons and shares all others with Oxygen – Leaves molecule with positively and negative charged ends Water is a Polar Molecule -has oppositely charged ends

55 5 slightly positive charge slightly negative charge hydrogen bond between (+) and (-) areas of different water molecules Water molecules form Hydrogen bonds

6 Water’s Properties Surface Tension Cohesion Adhesion Hydrophilic Hydrophobic Solid water (ice) is less dense than liquid Solvent Transparent

7 Cohesion How water molecules cling together by hydrogen bonding -water molecules stick together to climb up a stem – Cohesion refers to attraction to other water molecules.  responsible for surface tension  a measure of the force necessary to stretch or break the surface of a liquid  Hydrogen bonding allows water to behave like its coated w/ an invisible film

8 – Adhesion –how water molecules can stick to different things; – Water molecules stick to a plant’s stem & climb up a plant to reach the leaves to do photosynthesis – refers to attraction to other substances. Adhesion

9 Capillary action water evaporates from leaves = transpiration adhesion, cohesion and capillary action All thanks to hydrogen bonding! water taken up by roots

10 trees have specialized structures to transport water: xylem and phloem “plumbing” water molecules are “dragged” from the roots to the top of the tree by capillary action and cohesion: hydrogen bonds help water molecules to each other

11 Water is an effective solvent as it can form hydrogen bonds. – Water clings to polar molecules causing them to be soluble in water.  Hydrophilic - attracted to water (likes water); usually ionic or polar substances (ex. Salt)  Hydrophobic - repelled by water  Usually non-polar/non- ionic substances  ex. oil

12 “Universal” Solvent A liquid that is a completely homogeneous mixture of two or more substances is called a solution. – A sugar cube in a glass of water will eventually dissolve to form a uniform mixture of sugar and water. The dissolving agent is the solvent and the substance that is dissolved is the solute. – In our example, water is the solvent and sugar the solute. In an aqueous solution, water is the solvent.

13 Water transports molecules dissolved in it – Blood, a water-based solution, transports molecules of nutrients and wastes organisms – Nutrients dissolved in water get transported through plants – Unicellular organisms that live in water absorb needed dissolved substances

14 Solid water (ice) is less dense than liquid same mass but a larger volume Ice is less dense than water: the molecules are spread out to their maximum distance Density = mass/volume

15  water expands as it solidifies  water reaches maximum density at 4 degrees C  water freezes from the top down  organisms can still live in the water underneath the ice during winter Oceans and lakes don’t freeze solid because ice floats

16 Water is Transparent The fact that water is clear allows light to pass through it – Aquatic plants can receive sunlight – Light can pass through the eyeball to receptor cells in the back