Atoms and their structure
Labs n Labs are now online is a Google Docs folder n You can view the lab if you lose it (and you can copy and paste the procedure – so stop whining about having to rewrite it) n You can submit your Labs via Google Docs by sharing them with me
Another Greek n Aristotle - Famous philosopher n All substances are made of 4 elements –Fire - Hot –Air - light –Earth - cool, heavy –Water - wet n If you blend these in different proportions you can get all substances
Who ’ s Next? Late 1700’s - John Dalton- England. Late 1700’s - John Dalton- England. Elements are substances that can’t be broken down Elements are substances that can’t be broken down
Dalton ’ s Atomic Theory All matter is made of tiny indivisible particles called atoms. Atoms of the same element are identical, those of different atoms are different. Atoms of different elements combine in whole number ratios to form compounds. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.
Law of Definite Proportions n Each compound has a specific ratio of elements. n It is a ratio by mass. n Water is always 8 grams of oxygen for each gram of hydrogen.
Parts of Atoms n J. J. Thomson - English physicist n Made a piece of equipment called a cathode ray tube. –It is a vacuum tube - all the air has been pumped out. –A limited amount of other gases are put in
Thomson ’ s Experiment Voltage source +- Metal Disks
After connecting a battery to the tube, a beam appeared start at the negative end and move to the positive end Thomson ’ s Experiment Voltage source +-
Thomson ’ s Experiment He created an electrical charge around the tube and the beam always bent towards the positive + -
Voltage source Thomson ’ s Experiment He determined the beam was made of negative particles + -
Thomson ’ s Experiment n Used many different metals and gases n The beam was always the same n By the amount it bent he could find the ratio of charge to mass n It was the same with every material
Thompson ’ s Model n Found the electron. Couldn’t find positive particle(for a while). Couldn’t find positive particle(for a while). n Said the atom was like plum pudding. n A bunch of positive stuff, with the electrons able to be removed.
Millikan ’ s Experiment Atomizer Microscope - + Oil Metal Plates
Millikan ’ s Experiment Oil Atomizer Microscope - + Oil droplets
Millikan ’ s Experiment X-rays X-rays give some drops a charge by knocking off electrons
- Millikan ’ s Experiment +
They put an electric charge on the plates
Millikan ’ s Experiment Some drops would hover
Millikan ’ s Experiment Some drops would hover
Millikan ’ s Experiment From the mass of the drop and the charge on the plates, he calculated the charge on an electron
Rutherford ’ s Experiment n Ernest Rutherford English physicist. (1910) n Believed the plum pudding model of the atom was correct. n Wanted to see how big atom are n Shot alpha particles at gold foil which can be made a few atoms thick. n Alpha particles - positively charged particles.
Rutherford ’ s experiment n When the alpha particles hit a florescent screen, it glows.
Lead block Uranium Gold Foil Flourescent Screen
He Expected n The alpha particles to pass through without changing direction very much.
What he expected
What he got
How he explained it + n Atom is mostly empty space. n Small dense, positive piece at center. n Alpha particles are deflected by it if they get close enough. (like charges repel)
+
Bohr Model n Planetary model n Electrons in definite fixed orbits n How we currently draw atoms
Wave-Mechanical Model n Most modern model of the atom n Gives electrons properties of both particle and wave n Electrons with distinct amounts of energy moving in orbitals n Orbitals = region in which electron is likely to be located
Modern View n The atom is mostly empty space. n Two regions. n Nucleus- protons and neutrons. n Electron cloud- region where you might find an electron.