Water
Molecules and Bonding
The valence electrons of atoms interact to form bonds.
-Molecule = two or more atoms bonded together
-There are multiple types of bonds
-Ionic bond = The electrical attraction between positively and negatively charged ions
-When ions are formed they either give up an electron becoming positive or they take an electron becoming negative. This charge causes them to be attracted to oppositely charged ions. If an ion is negatively charged by one it will be attracted to an ion that is positively charged by one.
-Ionic bonds are not very strong. The atoms are not sharing electrons, they are only attracted to each other and stick in a crystal like pattern.
-Covalent Bond = When two or more atoms share valence electrons.
-Sometimes atoms will share their outermost electrons in order to complete their last shell. When they do this they are forming a covalent bond. This type of bond is very strong because the electrons are orbiting both atoms.
-Polar Covalent Bond = sometimes when a covalent bond is formed by atoms the electrons are not shared evenly. When the electrons spend more time around one atom than the other that atom becomes slightly negative and the other becomes slightly positive.
-Nonpolar Covalent Bond = When the electrons are shared evenly between the atoms.
-Water is a Polar Covalent Bond!
Water!
Water has many amazing properties that allow life on this earth possible. If water did not have the structure it does we would not exist!
Polar molecule- A molecule having a positive end and a negative end
-When water molecules stick to other water molecules it is called a hydrogen bond.
-Hydrogen Bond = When the positive ends of hydrogen stick to the negative end of oxygen. Hydrogen bonds are very weak.
-Cohesion = Water sticking to water because of the hydrogen bonds
-Cohesion causes surface tension which is the waters surface resisting being broken
Surface Tension
Surface Tension
-Adhesion = water sticking to other molecules other than water
Cohesion Penny Game!
Get into groups. You need one penny, a pipet, a paper towel, and a beaker of water. Set the penny (Lincoln up) on the paper towel. Now add drops of water from the pipet, one drop at a time. Try and fit as many drops of water as you can on top of the penny without it spilling over. The team that fits the most drops of water on top of the penny wins.
The bubble that the water created over the edge of the penny was a good example of cohesion. The water did not want to spill over because the hydrogen bonds where holding the water molecules to each other.
Questions & Answers:
Q: How is it that a tree that is 10m tall is able to bring water up to its leaves? Remember that trees d o not have any muscles
A: The leaves of the tree allow water vapor to leave through pores called stomata. As the water vapor escapes the water molecules pull the water molecules behind it (through cohesion). As the water molecules are pulled up by the escaping water molecules this creates a chain reaction all the way down to the roots. So the tree has to lose water to gain water.
Q: Why does a belly flop hurt? Why is it that you can easily slide your hand into water but if you slap it you can not break the surface?
A: Because of the hydrogen bonds of water a surface tension is created. This is the same principle as cohesion. The water does not want to let go of itself. When you slide your hand into the water you are pushing the hydrogen bonds apart but when you slap the water you are hitting the bonds before they get separated.
Q: how does a gas lantern work when the wick is above the fuel?
A: Because the wick is sitting in the fuel the fuel climbs the wick the same way water climbs a paper towel.
Applications to Everyday Life:
We can see the principles of cohesion and adhesion when we clean up water with a paper towel. The water will climb the paper towel. The water does this because of the adhesion of the water to the paper towel and the cohesion of the water to other water molecules
Teacher Demo:
Leave a paper towel in a beaker of water to watch the water climb out of the beaker
-Water is a polar molecule giving it many important features
-The most important feature of water is that it is less dense in its solid form than its liquid form
-Three states of matter
-Solid
-Liquid
-Gas
-Ice floats because water is more dense than ice
-Ice is 10% less dense than water so only 10% of ice breaches the water
-Since ice floats it is the surface of the ocean that freezes. The sheet of frozen ocean that forms insulates the water underneath which allows organisms to continue thriving under the ice without freezing.
Clouds have mass. They have a weight. That is why they can only float so high. The denser the cloud the lower it will float
High specific heat
-Because the water molecules are attracted to each other in a hydrogen bond it takes a lot of energy to break them apart. The hydrogen bonds need to be broken in order for water to change state...ice-water-steam
-This is referred to as high specific heat
-Water's high specific heat is important for many reasons. Many marine organisms need to maintain a consistent body temperature. Since it takes a large amount of energy to change the temperature of water the ocean's temperature changes subtly.
Teacher Demo:
Balloon over fire, one with water in it and one with only air in it. Will they both pop?
Water as a solvent
Because of water's polarity it makes a perfect solvent. It pulls ions apart separating them from their ionic bonds. This is why things dissolve in water.