1. Atoms Are They Real? June 2006 A Scorpacuda Presentation

2. What are atoms? Atoms are submicroscopic particles. Atoms are the basic building blocks of a the objects around us.

3. Are the real? Seven reasons to believe atomic theory: 1. We can count the number of atoms in an object – no fractional atoms. 2. Compounds of elements have simple ratios. 3. Velocity and mass of gas particles can be inferred. 4. Brownian Motion 5. Scintillation 6. X-Ray Diffraction shows crystal structures. 7. Atomic Force Microscope Images

4. Avogadro's Number Avogadro showed that the number of molecules or atoms in one gram is equal to the product of a large number and the molecular mass of the molecule (or atom).

5. Counting Atoms First we need to know: The weight of the object. The weight of the object. The chemical composition of the object. The chemical composition of the object.Then 1. Determine how many moles in the mass (divide weight by the amu) 2. Multiply this result by the Avogadro number 3. Multiply this result by the number of atoms in the molecule.

6. Example How many atoms are in 2 grams of water?A water molecule consists of one atom of oxygen (atomic weight 16) and two atoms of hydrogen (each with an atomic weight of 1). The atomic weight of a molecule of water is 18. Thus, one mole of water is that quantity of water which weighs 18 grams.

7. Roughly the same… Without determining the actual weight of a substance, a good rule of thumb to use is that a cubic centimeter of solid matter contains about 10 24 atoms. 1 cubic centimeter More or less - 10 24 Atoms

8. Simple Ratios Dalton’s atomic theory: matter is composed of atoms of several varieties – the elements of the Periodic Table. Observed simple ratios of elements in chemical compounds: H 2 O – two Hydrogen atoms to one Oxygen atom (water) H 2 O – two Hydrogen atoms to one Oxygen atom (water) NaCl – one Sodium atom to one Chlorine atom (table salt) NaCl – one Sodium atom to one Chlorine atom (table salt) H 2 SO 4 H 2 SO 4 etc. etc.

9. Ideal Gas Law If atoms exist, then they must have mass and velocity and kinetic energy. Bernoulli applied Newton’s laws of motion to explain the behavior of gases. Results of several scientists: P V = n R T

10. Gas Particles Double the number of gas particles, and the number of collisions between the particles and walls doubles – pressure doubles. TRY IT! Take some balloons and make a balloon rocket with string, straws. Take some balloons and make a balloon rocket with string, straws. Fill balloons with different amounts of air and release – record how far the balloons travel. Fill balloons with different amounts of air and release – record how far the balloons travel.

11. Gas Particles Increase the temperature of gas, the average velocity of gas particles increases. TRY IT! Stretch a balloon over a glass jar or graduated cylinder. Stretch a balloon over a glass jar or graduated cylinder. Place the jar in heated water – the balloon expands. Place the jar in heated water – the balloon expands.

12. Brownian Motion In 1905, Einstein showed mathematically that Brownian Motion could be modeled as resulting from a force of random collisions of atoms (or molecules). Simulation: Simulation: http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=41 http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=41 http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=41 Measurements: Measurements: http://www.deas.harvard.edu/weitzlab/research/brownian.html http://www.deas.harvard.edu/weitzlab/research/brownian.html http://www.deas.harvard.edu/weitzlab/research/brownian.html TRY IT! DigitalBlue Microscope has a movie mode. Gather pollen or carbon dust from flame on spoon and put particles in rubbing alcohol or distilled water. Observe the motion of the particles at highest resolution. (Don’t bump the microscope or table.) Make some movies of their motion. DigitalBlue Microscope has a movie mode. Gather pollen or carbon dust from flame on spoon and put particles in rubbing alcohol or distilled water. Observe the motion of the particles at highest resolution. (Don’t bump the microscope or table.) Make some movies of their motion.

13. Scintillation Scintillation is a flash of light produced in a transparent material by an ionization event. TRY IT! Crunching a Wintergreen LifeSaver® produces scintillation through the process of triboluminescence, making light with friction. Crunching a Wintergreen LifeSaver® produces scintillation through the process of triboluminescence, making light with friction. The Exploratorium has a tasty science snack: http://www.exploratorium.edu/cooking/candy/activity-lightning.html The Exploratorium has a tasty science snack: http://www.exploratorium.edu/cooking/candy/activity-lightning.html The Exploratorium’s explanation: The Exploratorium’s explanation: “When you crush sugar crystals, the stress in the crystal creates electric fields. Like the electric fields in a lightning storm, these electric fields can rip the outer electrons from molecules. When the molecules recombine with their electrons, they emit light. In addition to blue and violet light, the crunched crystals produce ultraviolet light, which you can’t see. Wintergreen oil converts ultraviolet light into visible blue light, making the light you can see brighter.”

14. X-Ray Crystallography Since the size of atoms is similar to the size of X-Ray wavelengths, the sizes and regular arrangements of atoms in crystals can be determined by X-Ray diffraction. http://www.uni-wuerzburg.de/mineralogie/crystal/teaching/ibasic_b.html

15. Atomic Force Microscopy

16. AFM Measurements from the Internet Are Consistent With Atomic Theory

17. Atomic Theory Summary Seven reasons to believe atomic theory: 1. We can count the number of atoms in an object – no fractional atoms. 2. Compounds of elements have simple ratios. 3. Velocity and mass of gas particles can be inferred. 4. Brownian Motion 5. Scintillation 6. X-Ray Diffraction shows crystal structures. 7. Atomic Force Microscope Images