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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.

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Presentation on theme: "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."— Presentation transcript:

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 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 carbon dioxide 2.66 g of oxygen combines with 1.0 g of carbon.  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 Cathode ray tube

8 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 8 of 25 Properties of cathode rays Electron m/e = -5.6857 x 10 -9 g coulomb -1

9 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 9 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.

10 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 10 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.

11 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 11 of 25 The nuclear atom Geiger and Rutherford 1909

12 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 12 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

13 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 13 of 25 The nuclear atom Rutherford protons 1919 James Chadwick neutrons 1932

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 -27 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. Biggest atom is 240 amu and is 50 Å across. Typical C-C bond length 154 pm (1.54 Å) Molecular models are 1 Å /inch or about 0.4 Å /cm

15 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 15 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 1.0073+1.602 x 10 -19 +1 Neutron 1.675 x 10 -27 1.0087 0 0 1 Å The nuclei of most atoms consist of protons and neutrons, which are called the nucleons. Atomic number: the number of protons defines the type of the element. The number of neutrons determines the isotope of an element.

16 The stability of the neutron In the stable nuclei the bound neutrons are stable. The free neutrons are unstable; they undergo beta decay with a half-life of just about 10.2 minutes (614 s). Quark structure: Feynmann diagram: Prof G. I. Csonka © 2009 General Chemistry: Chapter 2 Slide 16 of 25

17 Half life of the decaying free neutron Prof. G.I. Csonka © 2009 General Chemistry: Chapter 2 Slide 17 of 25 n 0 → p + + e − + ū e Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay:

18 Prentice-Hall © 2002 General Chemistry: Chapter 26 Slide 18 of 47 Energy – mass conversion Einstein (1905): E = mc 2 All energy changes are accompanied by mass changes (Δm) –In chemical reactions ΔE is too small to notice: Δm < 0.0000001 u (negligible). –In nuclear reactions ΔE > 1.1 MeV/nucleon. 1 MeV = 1.6022x10 -13 J If ΔE =1.4924x10 -10 J or 931.5 MeV then Δm = 1.0 u

19 Gabor I. Csonka © 2008General Chemistry: Chapter 26 Slide 19 of 47 Nuclear Binding Energy Total mass defect Positive binding energy: 0.0304 x 931.5 = 28.4 MeV Per nucleon: 28.4 / 4 = 7.1 MeV/nucleon

20 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 20 of 25 Isotopes, atomic numbers and mass numbers  To represent a particular atom we use the symbolism: A= mass numberZ = atomic number

21 Isotopes of an element Isotopes are different types of atoms (nuclides) of the same chemical element, Z, each having a different atomic mass (A: mass number) Same number of protons, but different number of neutrons. About 339 nuclides occur naturally on Earth, of which 256 (~75%) are stable. 3100 are known currently General Chemistry: Chapter 2 Slide 21 of 25

22 Az anyag22 The isotopes of the hydrogen 2 H=D 1 3 H=T 1 1 H=H 1 (t 1/2 ) : 12.33 years

23 Mass defect of the isotopes vs. energy Gábor I. Csonka © 2008General Chemistry: Chapter 26 Slide 23 of 47 ZAAtomic massMass defect MeV/nucleon H111.00783[amu] D122.014100.002391.11 T133.016050.009112.83 He233.016030.008292.57 244.002600.030387.07 Li366.015120.034355.33 377.016000.042135.61 Be499.012180.062446.46 B51010.012940.069516.47 51111.009310.081816.93 C61212.000000.098947.68 61313.003350.104257.47 61414.003240.113037.52

24 Prentice-Hall © 2002 General Chemistry: Chapter 26 Slide 24 of 47 Average Binding Energy as a Function of Mass Number

25 Prentice-Hall © 2002 General Chemistry: Chapter 26 Slide 25 of 47 Neutron-to-Proton Ratio (Segré diagram)

26 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 26 of 25 Measuring atomic masses

27 The relative atomic mass Unit: rest mass of carbon-12 is exactly12. It is the mean of the atomic masses over all the isotopes of the element weighted by isotopic abundance as found in a particular environment (standard: the earth crust). This number may be a fraction which is not close to a whole number, due to the averaging process. General Chemistry: Chapter 2 Slide 27 of 25

28 Isotopic abundance in the earth crust Az anyag Készítette: Dr. Csonka Gábor egyetemi tanár, csonkagi@gmail.com 28 ZA Atomic mass abundance%t 1/2 H11 1.00783 99.9885 D12 2.01410 0.0115 T13 3.01605 12.33 y He23 3.01603 24 4.00260 99.9999 Li36 6.01512 7.59 37 7.01600 92.41 Be49 9.01218 100.0000 B510 10.01294 19.9 511 11.00931 80.1

29 Isotopic abundance in the earth crust (2) Az anyag Készítette: Dr. Csonka Gábor egyetemi tanár, csonkagi@gmail.com 29 ZAAtomic mass abundance%t 1/2 C612 12.00000 98.9300 613 13.00335 1.0700 614 14.00324 5730 y N714 14.00307 99.6320 715 15.00011 0.3680 O816 15.99491 99.7570 817 16.99913 0.0380 818 17.99916 0.2050 Cl1735 34.96885 75.7800 1737 36.96590 24.2200

30 30 Boron (Z=5) Isotope composition 19.8 % 10 B m = 10.013 u 80.2 % 11 B m = 11.009 u (0.198  10.013 u) + (0.802  11.009 u) = 10.811 u The last digit is uncertain due to the variable isotope composition of boron in the earth crust (±0.007 u) Definition: An element consists of the mixture of its isotopes in the earth crust The relative atomic mass (atomic weight) of the boron element:

31 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 31 of 25 The Periodic table Alkali MetalsAlkaline EarthsTransition MetalsHalogensNoble Gases Lanthanides and Actinides Main Group

32 General Chemistry: Chapter 2 Slide 32 of 25 The Periodic Table Read relative 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.

33 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 33 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

34 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 34 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

35 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 35 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)

36 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 36 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

37 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 37 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

38 Prentice-Hall © 2002 General Chemistry: Chapter 2 Slide 38 of 25 Chapter 2 Questions 3, 4, 11, 22, 33, 51, 55, 63, 83.

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