“The Water Molecule” Why is Water So Special??

 Water is very unique… SPECIAL!  Water, H 2 O, is present in all three phases here on earth which is important for all life.  This triatomic molecule is made up of _________________ bonds

 The oxygen wants the electrons more than the hydrogens, making it _____________.  This is due to a large difference in electronegativity between O and H  This uneven sharing is what makes water a polar molecule.

 Polar molecules are attracted to one another by dipole interactions.  The (+) on one is attracted to the (-) on the other and vice versa.  This attraction is also very special and it is known as ___________________.  H-bonding is the reason for all of water’s special properties

 Water has a high surface tension (meaning the liquid phase does not have enough kinetic energy to break from to the gaseous phase) – what can you do to change this??  Water has a low vapor pressure  Water has a high specific heat capacity  Water has a high heat of vaporization  Water has a high boiling point  All of these special properties are from hydrogen bonding!!!

 The surface of water acts like a layer of skin  Because water has a high surface tension (due to ____________), it tends to bead up on itself ◦ Think about a freshly waxed car ◦ Think about a meniscus ◦ Think about spherical water droplets It holds this shape because a sphere has the smallest amount of surface area

 All liquids have surface tension, but water’s is higher than most.  This is why water tends to bead up on some surfaces rather than spread out  If you add a surfactant (a “surface acting agent”), it is possible to decrease water’s surface tension.

 When a detergent or soap is added to water, the detergent molecules interfere with the H- bonding between water molecules  This results in the beads of water collapsing and the water spreads out.

 Water also has an unusually high vapor pressure  Vapor Pressure is caused by molecules that escape the surface of the liquid and enter the gas phase.  Water tends to hang onto one another stronger because of _______________ which in turn lowers the vapor pressure.

 Without this high vapor pressure, water in the oceans, lakes, and rivers would all rapidly break free from the liquid phase and immediately evaporate!!

 What is specific heat??  Water’s specific heat is 4.18 J/g⁰K ◦ Which means it takes

 Because of hydrogen bonding, the specific heat capacity is higher than most other substances.  Iron’s Cp is only J/g*K, which means for the same increase in temp as water, Fe only need Joules of energy.  Water’s high Cp helps to moderate daily air temperature around large bodies of water

 On a warm day, water absorbs heat from its warmer environment, lowering the air temperature  On a cold night, heat is transferred from the water to its cooler environment, raising the air temperature  This property makes water a very good storage medium for solar energy

1. Describe the hydrogen bonding between molecules in water. 2. How is hydrogen bonding responsible for the high surface tension and low vapor pressure of water?? 3. What is a surfactant? How does it affect the surface tension of water? 4. What is the specific heat capacity of water? What does it mean? Why is it a GOOD thing it is higher than most other things?

Vocab Sheets Due