Properties of Water Polar covalent bond – unequal sharing of electrons…creates a dipole in a molecule and results in dipole-dipole intermolecular forces between molecules H bonding- strongest intermolecular force specifically caused by the high electronegativity difference between F, O or N and Hydrogen atoms. A great example of a molecule with polar covalent bonds and H bonding is water.

Dipole-Dipole and H-Bonding Intermolecular Forces Properties of Water Dipole-Dipole and H-Bonding Intermolecular Forces Hydrogen Bond Covalent Bond

Water is the solvent of Life! Properties of Water Universal Solvent Water is the solvent of Life! Solute – substance dissolved in a solvent to form a solution Solvent – fluid that dissolves solutes Example: Ice Tea – water is the solvent and tea and sugar the solutes Since water is polar it can dissolve polar organic molecules and ionic compounds (Like dissolves like)

Properties of Water cohesion = water attracted to other water Cohesion, Adhesion and Surface Tension cohesion = water attracted to other water molecules because of polar properties (beading of water) adhesion = water attracted to other materials (meniscus is curved up when water touches glass in a graduated cylinder) surface tension = water molecules at the surface have intermolecular forces between them (pain of a belly flop)

Properties of Water Capillary Action Because water has both adhesive and cohesive properties, capillary action is present. Capillary Action = water’s adhesive property is the cause of capillary action. Water is attracted to some other material and then through cohesion, other water molecules move too as a result of the original adhesion. Ex: Think water in a straw. Water moves through trees this way Water in tall trees cannot get to the top of the tree without capillary action. There is no pump pulling the water up. Sequoia trees in California in danger due to global warming.

Properties of Water High boiling and melting point Because water is so polar, it has London, Dipole-Dipole and H bonding intermolecular forces between molecules 0oC melting point to 100 oC boiling point is a 100 degree range in temperature for the existence of liquid water. Thus water on Earth is primarily in liquid form- oceans, rivers and lakes. Life is possible when reactions can occur quickly and reactions in solid ice are too slow and gaseous vapor molecules are too far to collide. Liquid water is essential for life. Life is believed to have originated in a pond or an ocean.

Properties of Water High Heat Capacity In order to raise the temperature of water, the average molecular speed has to increase. It takes much more energy to raise the temperature of water compared to other solvents because hydrogen bonds hold the water molecules together! Water has a high heat capacity. “The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius.” This means that the temperature of water does not vary much when there is addition or removal of heat….thus water has a very large range where it is liquidl High Heat Capacity Imagine a universe where water does not have high heat capacity…every day the sun’s energy would be enough to boil all the oceans away and every night it would rain down a whole ocean. The drastic changes would make life difficult to get established.

Properties of Water Density Water is less dense as a solid! This is because the hydrogen bonds are more numerous in ice than water– each molecule of solid water is bound to four of its neighbors. Spacing required spreads out molecules. Solid – water molecules are bonded together – space between fixed Liquid – water molecules are constantly bonding and rebonding – space is always changing Almost all other substances, solid is more dense then liquid

Properties of Water Density Since ice is less dense than water, ice floats on water in lakes and acts as thermal insulation against the cold for the rest of the lake underneath. It can be -20oC and the top layer of the lake is frozen but below the ice there is water allowing fish, plants and microorganisms to survive the winter. Life does not have to restart from scratch after every winter. Insulation allows protection of life underneath. If ice forms slowly, more hydrogen bonds can be made and the water molecules get very far apart to maximize the number of hydrogen bonds…this results in the formation of

Properties of Water So, can you name all of the properties of water? 1. Great solvent 2. Adhesion/ Cohesion/High surface tension/ Capillary action 3. High melting point/high boiling point 4. Able to regulate (stabilize) temperature (High heat capacity)- with the + of heat…temperature stays constant. With the – of heat, temperature stays constant 5. Less dense as a solid than a liquid