8th Grade Critical Skills
1. Water
a) One molecule of water is made of 2 hydrogen atoms and 1 oxygen atom
b) Chemical symbol for oxygen- O
c) Chemical symbol for hydrogen –H
2. Compound- two or more chemical elements chemically bound together
3. Chemical formula- a description of how many elements are in a compound
b) The chemical formula for water is H2O
c) For water, 1 g = 1 mL = 1 cm3 = 1 cc
4. Archimedes of Samos
a) Considered to be one of the greatest scientists of ancient Greece
b) Began the development of scientific notation
c) Eureka! – The Story of the Crown of King Minos
d) Discovered the Law of Density
Density = Mass (g) / Volume (mL or cm3)
e) Law of Volume of Rectangles (regularly- shaped objects)
Volume = Length x Width x Height
5. Directly inspired Galileo and Isaac Newton to investigate the mathematics of motion
6. Specific gravity
a) The ratio of the density of an object to the density of a standard, usually water
b) Specific gravity is a numeric (it has no units)
7. ‘Mystery’ Knowledge That Few Take Notice Of
a) “What you see on the macro-scale, you see on the micro-scale’.” (Plato)
b) For example, let's compare the atom to our solar system
(1) There is a lot of space between the Sun and the planets. There is also a lot of space between the nucleus and the electrons in an atom.
(2) The planets travel in elliptical orbits around the Sun. The electrons travel in elliptical orbits around the nucleus of the atom.
(3) The planets spin (rotate) on their axes as they travel (revolve) around the Sun. Likewise, the electrons spin (rotate) as they travel (revolve) around the nucleus.
Professor's Note: You learned in class that what we see on the macro-scale (i.e., the solar system), we will often see on the micro-scale (i.e., the atom). If this observation is a universal principle, I suspect that both either both gravity and electromagnetism are found in both scales or gravity is simply a result of electromagnetism. My thoughts are included here to demonstrate the way I am trying to teach you to think about the natural world around you. -Mr. Mac
8. Just as there is a lot of space inside the atom, there is a lot of space between molecules
9. Example: Salt dissolving in water
a) The salt crystals break down into sodium and chlorine ions
b) The sodium and chlorine ions go into the empty spaces between the water molecules
c) Ion- a charged atom that has lost or gained one or more electrons.
10. Table Salt
a) The chemical name of table salt is ‘sodium chloride’
b) The chemical formula of sodium chloride is ‘NaCl’
c) The chemical symbol for sodium is ‘Na’
d) The chemical symbol for chlorine is ‘Cl’
e) A molecule of sodium chloride contains one sodium atom and one chlorine atom
f) Salt water is an example of a solution
11. Salinity
a) Salinity is defined as a description of how much salt is dissolved in a given amount of water
b) The average salinity of fresh water is 0%
c) The average salinity of water in the Atlantic Ocean is 35%
d) The average salinity of water in the Dead Sea is 350% (This water is considered saturated- all of the empty space between the water molecules is filled up with dissolved salt)
Floating in a Swimming Pool & the Dead Sea
Note how much of the swimmer's body remains above water in the Dead Sea video clip. The space between the water molecules in Dead Sea water is totally occupied. This leaves no space for your body so you float higher and have trouble swimming in it. The Dead Sea is about eight times saltier than the Atlantic Ocean.
12. The density of ocean water also limits the amount of cargo a ship can carry.
13. Specific Gravity
a) This is the ratio of the density of an object or substance to the density of a standard, usually water.
b) If the specific gravity is less than 1, that object will float.
c) If the specific gravity is greater than 1, that object will sink.
14. Conductivity
a) This is a measure of how well something can conduct electricity
b) Salt water is a better electrical conductor than fresh water
c) The human body has salt water in it and can conduct electricity very well
d) Most materials than can conduct electricity can also conduct heat
15. When working on your Putt-Putt Boat, it will help if you know some boating terms.
a) Bow- the front of the hull
b) Stern- the back of the hull
c) Hull- the body of the boat that sets in the water
d) Starboard- the right side of the boat
e) Port- the left side of the boat
Salt Dissolving in Water
Chemical Reaction Between Sodium and Chlorine to Form Sodium Chloride (Table Salt)
