2 Just How Small is an Atom? You don’t need to write.A speck 0.1 mm in diameter (about half the size of a period at the end of the sentence) requires one million atoms.It would require a million atoms, edge to edge, to match the thickness of a page of paper.
3 Can you see an atom?Technically, you cannot "see" anything smaller than the shortest wavelength of light that you can see it with.But there are ways to "visualize" it, like Atomic Force Microscopy. But these are all just measurements converted to computer images, and are not in any real sense "seeing" the atom.You can't see atoms in any normal sense of using an optical microscope.You don't get an optical image, but it does allow you to map out an image of the atoms of a molecule. To do this you use a metallic tip which interacts with the atoms you want to image. As you move the tip over the atoms, you pass a current, called a tunneling current, between the tip and the atom. This current is extremely sensitive to the distance between the atom and the tip.
4 - REMEMBER FROM: Elements, Mixtures, and Compounds - - a pure substance made up of one type of atom.- organized on periodic table- each element has a uniquenumber of protons…its atomic number
5 Atomic Structure: Atoms contain three subatomic particles… 1. Protons… 2. Neutrons…3. Electrons…positive chargeThese are located in NUCLEUS!neutral chargenegative chargeElectrons surround the nucleus in orbitals
6 Atomic StructureAn atom is considered electrically neutral. Electrically neutral means the number of protons (+) = the number of electrons (-)4 red protons = 4 blue electrons
7 Properties of Subatomic Particles SymbolRelative electrical chargeRelative massActual mass (g)Electrone-1-1/18409.11 × 10-28Protonp+1+11.67 × 10-24Neutronn0Protons and Neutrons have the same mass.
8 A. Discovery of the AtomErnest Rutherford discovered the nucleus by shooting alpha particles (have a positive charge) at a very thin piece of gold foil.He predicted that the particles would go right through the foil at some small angle.
10 Rutherford’s Gold Foil Experiment some particles (1/8000) bounced back from the foilthis meant there must be a “powerful force” in the foil to hit particle backPredicted Results Actual Results
11 Discovery of the AtomPurpose: The students will find the shape of different items and relate this to the early scientist that made discoveries about the shape and size of the atom. Procedure: 1. Title the left side of your spiral Discovery of the Atom. 2. For each item you will write the letters then draw your predicted shape of the item. 3. Then you will write 1 sentence describing why they think your prediction is the shape of the item. A: Item in brown bag – Use your hands to feel the shape of the item. B: Item in clay – Using the toothpicks provided find the shape of the object enclosed in the modeling clay. C: Black box – Maneuver the black box with a marble inside to discover the shape of the object enclosed.
21 You must know how to find: C. Nuclear SymbolsYou must know how to find:# of protons = atomic numbermass # = # of n0 + # of p+ (atomic #)What’s in the nucleus of the atom# of electrons = # of protons (in a neutral atom)Boron5B10.811atomic number(Not the same as the mass #)(average) atomic mass
22 How to write a Nuclear Symbol Charge if ionElement SymbolBMass Number= p+ + n0-3115Atomic Number= p+
23 C. Nuclear Symbols Chlorine-37 atomic #: mass #: # of protons: # of electrons:# of neutrons:173720
24 Cl Mg Nuclear Symbol Examples 35 17 27 12 17 35 17 17 18 12 27 12 12 Number of ProtonsNumber of ElectronsNumber of NeutronsAtomic NumberMass Number1735171718Mg2712Number of ProtonsNumber of ElectronsNumber of NeutronsAtomic NumberMass Number1227121215
26 E. Average Atomic Massweighted average of all naturally occuring isotopeson the Periodic Tableround to 2 decimal placesAvg.AtomicMass
27 E. Average Atomic MassEX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.Avg.AtomicMass16.00amu
28 E. Average Atomic MassEX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.Avg.AtomicMass35.40 amu
29 Example:A sample of cesium is 75% 133Cs, 20% 132Cs and 5% 134Cs. What is the average atomic mass?Answer:.75 x 133 = 99.75.20 x 132 = 26.4.05 x 134 = 6.7= average atomic mass
30 II. The Periodic TablePeriodic Law – properties of elements can be predicted by their position on the periodic table
31 A. History of the Periodic Table Dmitri Mendeleev (1871)Developed the first periodic tableIt was arranged by atomic mass because atomic number had not been discoveredHe was able to predict properties of elements31
32 A. History of the Periodic Table Henry Moseley (1913)- developed the modern periodic table- arranged in order of increasing atomic number32
33 B. Organization of the Periodic Table horizontal rows numbered 1 - 7Energies of outermost electrons are similar33
34 B. Organization of the Periodic Table Groups/ Familiesvertical columnshave similar chemical & physical properties34