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ATOMIC STRUCTURE, NUCLEAR CHEMISTRY & UNIT 6 He asked this question: If you break a piece of matter in half, and then break it in half again, how many.

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Presentation on theme: "ATOMIC STRUCTURE, NUCLEAR CHEMISTRY & UNIT 6 He asked this question: If you break a piece of matter in half, and then break it in half again, how many."— Presentation transcript:

1

2 ATOMIC STRUCTURE, NUCLEAR CHEMISTRY & UNIT 6

3 He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms.

4 Aristotle – famous philosopher Believed all substances made of 4 elements Blending these in different proportions to get all substances Fire – hot air – light Earth – cool, heavy Water – wet

5 Late 1700s – John Dalton Teacher who summarized results of his experiments and those of others Combined idea of elements with that of atoms

6 1.All matter is made of tiny, indivisible particles call atoms 2.Atoms of the same element are identical 3.Atoms of different elements combine in whole number ratios to form compounds 4.Chemical reactions involve the rearrangement of atoms. No atoms are created or destroyed.

7 Smallest particle of an element that still retains the properties of that element

8 In 1897, Thompson discovered the first component part of the atom: the electron, a particle with a negative electric charge. In 1904, he proposed an initial model of an atom, since nicknamed "Thompsons pudding". In 1904, he proposed an initial model of an atom, since nicknamed "Thompsons pudding". He imagined the atom as a sphere full of an electrically positive substance mixed with negative electrons "like the raisins in a cake".

9 Voltage source Vacuum tube Metal Disks

10 Voltage source Vacuum tube Metal Disks -+

11 Voltage source -+

12 -+

13 -+

14 -+ Passing an electric current makes a beam appear to move from the negative end to the positive end

15 Voltage source -+ Passing an electric current makes a beam appear to move from the negative end to the positive end

16 Voltage source -+ Passing an electric current makes a beam appear to move from the negative end to the positive end

17 Voltage source -+ Passing an electric current makes a beam appear to move from the negative end to the positive end

18 Voltage source -+ By adding an electric field…

19 Voltage source -+ By adding an electric field… + -

20 Voltage source -+ By adding an electric field… + -

21 Voltage source -+ By adding an electric field he found that the moving pieces were negative + -

22 Oil Atomizer Oil droplets Telescope - +

23 X-rays X-rays give some electrons a charge.

24 From the mass of the drop and the charge on the plates, he calculated the mass of an electron

25 Proton – positively charged pieces 1840 times heavier than electrons, discovered by E. Goldstein Neutron – no charge but the same mass as a proton, by J. Chadwick Where are these pieces?

26 Ernest Rutherford – English physicist Believed in the plum pudding model of the atom

27 Wanted to see how large the positive particles are Used radioactivity Shot alpha particles at gold foil Alpha particles – positively charged pieces,

28 When an alpha particle hits a fluorescent screen it glows

29 Lead block Uranium Gold Foil Fluorescent Screen

30 He expected the alpha particles to pass through without changing direction very much Because… The positive charges were thought to be spread out evenly Not enough to stop the alpha particles

31 What he expected

32 Because

33 He thought the mass was evenly distributed in the atom

34 Since he thought the mass was evenly distributed in the atom

35 What he got

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

37 +

38 Since most of the particles went through, it was mostly empty space Because the alpha particles turned so much, the nucleus was heavy Small volume, big mass, big density The small dense positive area is the nucleus

39

40 Unit 6 – Part 2

41 NameSymbolChargeRelative Mass Actual Mass (g) Electrone-e- 1/ x Protonp+p x Neutronn0n x

42 Atomic Number – the number of protons in the nucleus All protons are alike so… # of protons determines kind of atom The same as the number of electrons in a neutral atom

43 Mass number = # of protons + # of neutrons Protons and neutrons account for most of the mass of an atom

44 Contain the element symbol, mass number, and atomic number X Mass number Atomic number

45 Find: # of protons # of neutrons # of electrons Atomic # Mass # F 9 19

46 Find: # of protons # of neutrons # of electrons Atomic # Mass # Br 35 80

47 If an element has 91 protons and 140 neutrons, what is the Atomic # Mass # # of electrons Complete symbol

48 Dalton was wrong Atoms of the same element can have different numbers of neutrons This means different mass numbers Called isotopes

49 Can also put mass # after name of the element Carbon-12 Carbon-14 Uranium-235

50 There are different kinds of oxygen atoms. More concerned with the average atomic mass

51 Based on the abundance of each in nature Do not use grams because numbers would be too small

52 Use the atomic mass unit (amu) One twelfth of a carbon-12 atom Each isotope has its own atomic mass Determine average from % abundance

53 Multiply atomic mass by % abundance then add results

54 Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of amu and the rest has a mass of amu.

55 Magnesium has 3 isotopes % has a mass of % has a mass of The rest has a mass of amu. What is the atomic mass?

56 Is not a whole number because it is an average The number on the periodic table


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