2. Chapter 2 Atoms, Molecules, and Ions

3. Laws n Conservation of Mass n Law of Definite Proportion- compounds have a constant composition.  Carbon tetrachloride is always 1 atom carbon per 4 atoms chlorine.  They react in specific ratios by mass. n Multiple Proportions- When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers.  The ratio of the masses of oxygen in H 2 O and H 2 O 2 will be a small whole number (“2”).

4. Dalton’s Atomic Theory 1) Elements are made up of atoms 2) Atoms of each element are identical. Atoms of different elements are different. 3) Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom. 4) Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.

5. n Gay-Lussac- under the same conditions of temperature and pressure, compounds always react in whole number ratios by volume. n Avagadro- interpreted that to mean at the same temperature and pressure, equal volumes of gas contain the same number of particles. n (called Avagadro’s Hypothesis) A Helpful Observation

6. Thomson’s Experiment Voltage source +-

7. Thomson’s Experiment Voltage source +-

8. n Passing an electric current makes a beam appear to move from the negative to the positive end. Thomson’s Experiment Voltage source +-

9. Thomson’s Experiment n By adding an electric field

10. Voltage source Thomson’s Experiment n By adding an electric field, he found that the moving pieces were negative + -

11. Thomson’s Model n Found the electron. n Couldn’t find positive (for a while). n Said the atom was like plum pudding. n A bunch of positive stuff, with the electrons able to be removed.

12. Millikan’s Experiment Oil Atomizer Oil droplets Telescope - +

13. Millikan’s Experiment X-rays X-rays give some electrons a charge.

14. Millikan’s Experiment Some drops would hover From the mass of the drop and the charge on the plates, he calculated the mass of an electron

15. Radioactivity n Discovered by accident n Bequerel n Three types –alpha- helium nucleus (+2 charge, large mass) –beta- high speed electron –gamma- high energy light

16. Rutherford’s Experiment n Used uranium to produce alpha particles. n Aimed alpha particles at gold foil by drilling hole in lead block. n Since the mass is evenly distributed in gold atoms alpha particles should go straight through. n Used gold foil because it could be made atoms thin.

17. Lead block Uranium Gold Foil Florescent Screen

18. What he expected

19. Because

20. Because, he thought the mass was evenly distributed in the atom.

21. What he got

22. How he explained it + n Atom is mostly empty n Small dense, positive piece at center. n Alpha particles are deflected by it if they get close enough.

23. +

24. 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.

25. The Mass and Change of the Electron, Proton, and Neutron

26. Sub-atomic Particles n Z - atomic number = number of protons determines type of atom. n A - mass number = number of protons + neutrons. n Number of protons = number of electrons if neutral.

27. Symbols X A Z Na 23 11

28. Covalent Chemical Bonds n The forces that hold atoms together are called chemical bonds. n Covalent bonding - sharing electrons. n Makes molecules. n Chemical formula- the number and type of atoms in a molecule. n C 2 H 6 - 2 carbon atoms, 6 hydrogen atoms, n Structural formula shows the connections, but not necessarily the shape.

29. Ionic Bonding Cation: A positive ion Mg 2+, NH 4 + Anion: A negative ion Cl , SO 4 2  Ionic Bonding: Force of attraction between oppositely charged ions.

30. Hydrates n Some salts trap water crystals when they form crystals. n These are hydrates. n Both the name and the formula needs to indicate how many water molecules are trapped. n In the name we add the word hydrate with a prefix that tells us how many water molecules.

31. Hydrates n In the formula you put a dot and then write the number of molecules. Calcium chloride dihydrate = CaCl 2  2  Calcium chloride dihydrate = CaCl 2  2  Chromium (III) nitrate hexahydrate = Cr(NO 3 ) 3  6H 2 O Chromium (III) nitrate hexahydrate = Cr(NO 3 ) 3  6H 2 O