Starter S-23

1. Starter S-23 What are the 3 parts of an atom?

2. Atomic Structure Chapter 4

3. 4.1 Defining the Atom Chapter 4

4. 4.1 Defining the Atom Early Model • Democritus (460-370 B.C.) – matter consists of tiny indivisible, unchangeable particles • first to coin term atom • Did not use scientific method

5. 4.1 Defining the Atom Dalton’s Atomic Theory Dalton (1766-1844) – used scientific method to support Democritus’s ideas • Most famous for work with the atom, but also worked with • Weather • Color blindness

6. 4.1 Defining the Atom Postulates of Dalton’s Atomic Theory 1. Elements are composed of tiny indivisible particles called atoms • Atoms of the same element are the same, they are different from atoms of any other element • Atoms combine in simple whole number ratios to form compounds • Chemical reactions join, separate, or recombine atoms, the atoms never change

7. 4.1 Defining the Atom Atoms are very small Can only be observed with a scanning tunneling microscope Size is 1 x 10-10m Or 0.0000000001 m

8. 4.2 Structure of the Nuclear Atom Chapter 4

9. 4.2 Structure of the Nuclear Atom Three kinds of sub atomic particles Proton, Neutron, Electron Actually many more

10. 4.2 Structure of the Nuclear Atom Three kinds of sub atomic particles Proton, Neutron, Electron Actually many more Fermions Leptons Quarks Hadrons Baryons Meson Bosons

11. Cathode Ray Simulation 4.2 Structure of the Nuclear Atom Electron Discovered by JJ Thompson (1897) Negative charge Very small mass (we will call it 0) Discovered using a cathode ray tube Deflects toward the positive plate, so stream of negative particles

12. 4.2 Structure of the Nuclear Atom Robert Millikan – preformed experiments to calculate the amount of negative charge

13. 4.2 Structure of the Nuclear Atom Proton Positive Charge Relative Mass of 1 (1840 x electron) Found in Nucleus Discovered in 1886 by Eugen Goldstein

14. Starter S-24 What did each of these scientists contribute to our understanding of the atom? • Democritus • JJ Thompson • Robert Millikan • James Dalton

15. 4.2 Structure of the Nuclear Atom Neutron Neutral Found in nucleus Relative mass is 1 Discovered in 1932 by James Chadwick

16. 4.2 Structure of the Nuclear Atom In Summary

17. 4.2 Structure of the Nuclear Atom In Summary

18. 4.2 Structure of the Nuclear Atom The Nucleus Originally believed that all the particles were spread out evenly 1911 Rutherford’s Gold Foil Experiment proved that matter is mostly empty space with a dense positive nucleus Gold Foil Experiment Scattering

19. 4.2 Structure of the Nuclear Atom The Rutherford Model of the Atom • The atom is mostly empty space • All the positive charge and most of the mass is concentrated in a small nucleus • Protons and neutrons are in the nucleus Called the Nuclear Atom Does not explain electrons

20. 4.3 Distinguishing Among Atoms Chapter 4

21. 4.3 Distinguishing Among Atoms Protons – determine what element is the atom is Hydrogen – 1 proton Still Hydrogen if you add 1 Neutron 2 Neutron

22. 4.3 Distinguishing Among Atoms However, if we add a proton The element is now Helium

23. 4.3 Distinguishing Among Atoms Atomic number – the number of protons in an element This is called the value of Z A is the mass number X is the symbol Hydrogen would be

24. 4.3 Distinguishing Among Atoms Atomic number – the number of protons in an element This is called the value of Z A is the mass number X is the symbol Hydrogen would be

25. 4.3 Distinguishing Among Atoms Atomic number – the number of protons in an element This is called the value of Z A is the mass number X is the symbol Helium would be

26. 4.3 Distinguishing Among Atoms Atomic number – the number of protons in an element This is called the value of Z A is the mass number X is the symbol Helium would be

27. 4.3 Distinguishing Among Atoms In a uncharged (neutral) atom, the number of protons equals the number of electrons If extra electrons are added Atom becomes negative

28. 4.3 Distinguishing Among Atoms In a uncharged (neutral) atom, the number of protons equals the number of electrons If extra electrons are added Atom becomes negative

29. 4.3 Distinguishing Among Atoms In a uncharged (neutral) atom, the number of protons equals the number of electrons If extra electrons are added Atom becomes negative If electrons are lost Atom becomes positive

30. 4.3 Distinguishing Among Atoms In a uncharged (neutral) atom, the number of protons equals the number of electrons If extra electrons are added Atom becomes negative If electrons are lost Atom becomes positive

31. Starter S-25 How many protons and electrons are in the following atom?

32. 4.3 Distinguishing Among Atoms Mass Number (A) is the total number of protons and neutrons So hydrogen with no neutrons With one neutron

33. 4.3 Distinguishing Among Atoms So the number of neutrons is Neutrons = A – Z Isotope – same element, but different numbers of neutrons, and different mass numbers

34. 4.3 Distinguishing Among Atoms

35. 4.3 Distinguishing Among Atoms There are two isotopes of Carbon. One has a mass of 12, and the other a mass of 13. What is the symbol for Carbon-12? How many neutrons N = A – Z N = 12 – 6 = 6

36. 4.3 Distinguishing Among Atoms Atomic Mass Determined using a mass spectrometer Masses are given relative to the mass Carbon-12 1 amu (Atomic Mass Unit) = 1/12 the mass of 126C Mass Spectrometer

37. 4.3 Distinguishing Among Atoms The atomic mass is a weighted average of the mass of different isotopes Depends on the mass of the isotopes and how common they are Carbon-12 mass = 12.000, abundance is 98.89% Carbon-13 mass = 13.003, abundance is 1.11%

38. 4.3 Distinguishing Among Atoms Your turn Chlorine-35, mass=34.969, abundcance=75.77% Chlorine-37, mass=36.966, abundance=24.23%

39. 4.3 Distinguishing Among Atoms The Periodic Table Arranged by increasing atomic number Columns by similar chemical properties Periodic Table

40. 4.3 Distinguishing Among Atoms Period – horizontal row Group (family) – vertical row Periodic – chemical properties repeat