1. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 1 of 25 Chapter 2: Atoms and the Atomic Theory Philip Dutton University of Windsor, Canada Prentice-Hall © 2002 General Chemistry Principles and Modern Applications Petrucci Harwood Herring 8 th Edition

2. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 2 of 25 Contents Early chemical discoveries Electrons and the Nuclear Atom Chemical Elements Atomic Masses The Mole

3. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 3 of 25 Early Discoveries Lavoisier 1774Law of conservation of mass Proust 1799Law of constant composition Dalton 1803-1888 Atomic Theory

4. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 4 of 25 Dalton’s Atomic Theory  Each element is composed of small particles called atoms. ‚Atoms are neither created nor destroyed in chemical reactions.  All atoms of a given element are identical „Compounds are formed when atoms of more than one element combine

5. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 5 of 25 Consequences of Dalton’s theory  In forming carbon monoxide, 1.33 g of oxygen combines with 1.0 g of carbon.  In the formation of hydrogen peroxide 2.66 g of oxygen combines with 1.0 g of hydrogen.  Law of Definite Proportions: combinations of elements are in ratios of small whole numbers.

6. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 6 of 25 Behavior of charges

7. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 7 of 25 Properties of cathode rays Electron m/e = -5.6857 x 10 -9 g coulomb -1

8. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 8 of 25 Charge on the electron  From 1906-1914 Robert Millikan showed ionized oil drops can be balanced against the pull of gravity by an electric field.  The charge is an integral multiple of the electronic charge, e.

9. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 9 of 25 Radioactivity Radioactivity is the spontaneous emission of radiation from a substance.  X-rays and  -rays are high-energy light.   -particles are a stream of helium nuclei, He 2+.   -particles are a stream of high speed electrons that originate in the nucleus.

10. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 10 of 25 The nuclear atom Geiger and Rutherford 1909

11. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 11 of 25 The  -particle experiment  Most of the mass and all of the positive charge is concentrated in a small region called the nucleus.  There are as many electrons outside the nucleus as there are units of positive charge on the nucleus

12. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 12 of 25 The nuclear atom Rutherford protons 1919 James Chadwick neutrons 1932

13. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 13 of 25 Atomic Diameter 10 -8 cm Nuclear diameter 10 -13 cm Nuclear Structure ParticleMassCharge kgamuCoulombs(e) Electron 9.109 x 10 -31 0.000548–1.602 x 10 -19 –1 Proton 1.673 x 10 -27 1.00073+1.602 x 10 -19 +1 Neutron 1.675 x 10 -27 1.00087 0 0 1 Å

14. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 14 of 25 Scale of Atoms Useful units:  1 amu (atomic mass unit) = 1.66054 x 10 -24 kg  1 pm (picometer) = 1 x 10 -12 m  1 Å (Angstrom) = 1 x 10 -10 m = 100 pm = 1 x 10 -8 cm  The heaviest atom has a mass of only 4.8 x 10 -22 g and a diameter of only 5 x 10 -10 m.

15. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 15 of 25 Isotopes, atomic numbers and mass numbers  To represent a particular atom we use the symbolism: A= mass numberZ = atomic number

16. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 16 of 25 The Periodic table Alkali MetalsAlkaline EarthsTransition MetalsHalogensNoble Gases Lanthanides and Actinides Main Group

17. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 17 of 25 The Periodic Table Read atomic masses. Read the ions formed by main group elements. Read the electron configuration. Learn trends in physical and chemical properties. We will discuss these in detail in Chapter 10.

18. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 18 of 25 The Mole Physically counting atoms is impossible. We must be able to relate measured mass to numbers of atoms. –buying nails by the pound. –using atoms by the gram

19. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 19 of 25 Avogadro’s number  The mole is an amount of substance that contains the same number of elementary entities as there are carbon-12 atoms in exactly 12 g of carbon-12. N A = 6.02214199 x 10 23 mol -1

20. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 20 of 25 Molar Mass The molar mass, M, is the mass of one mole of a substance. M (g/mol 12 C) = A (g/atom 12 C) x N A (atoms 12 C /mol 12 C)

21. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 21 of 25 Combining Several Factors in a Calculation—Molar Mass, the Avogadro Constant, Percent Abundance. Potassium-40 is one of the few naturally occurring radioactive isotopes of elements of low atomic number. Its percent natural abundance among K isotopes is 0.012%. How many 40K atoms do you ingest by drinking one cup of whole milk containing 371 mg of K? Want atoms of 40 K, need atoms of K, Want atoms of K, need moles of K, Want moles of K, need mass and M(K). Example 2-9

22. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 22 of 25 Convert strategy to plan m K (mg) x (1g/1000mg)  m K (g) x 1/M K (mol/g)  n K (mol) Convert mass of K(mg K) into moles of K (mol K) Convert moles of K into atoms of 40 K n K (mol) x N A  atoms K x 0.012%  atoms 40 K n K = (371 mg K) x (10 -3 g/mg) x (1 mol K) / (39.10 g K) = 9.49 x 10 -3 mol K and plan into action atoms 40 K = (9.49 x 10 -3 mol K) x (6.022 x 10 23 atoms K/mol K) x (1.2 x 10 -4 40 K/K) = 6.9 x 10 17 40 K atoms

23. Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 23 of 25 Chapter 2 Questions 3, 4, 11, 22, 33, 51, 55, 63,