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The Atom and The Periodic Table

The Atom and The Periodic Table. 1932 James Chadwick British Found an electrically neutral particle which resides in the nucleus and has almost the same mass as the proton. He named this “neutral proton” the neutron. James Chadwick. +. Discovery of the Neutron. +.

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The Atom and The Periodic Table

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  1. The Atom and The Periodic Table

  2. 1932 James Chadwick • British • Found an electrically neutral particle which resides in the nucleus and has almost the same massas the proton. He named this “neutral proton” the neutron. James Chadwick

  3. + Discovery of the Neutron + James Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted.

  4. Atom: • smallest particle of an element that retains the chemical properties of the element. • -can be broken down, however they would lose their chemical identity 1 teaspoon of H2O (1 mL) contains 3x as many atoms as the Atlantic Ocean contains teaspoons of H2O!!!!!! The Atom

  5. One of Dalton’s postulates said that, “All atoms of the same element are identical.” • (i.e. same mass and properties) • IS THIS TRUE? • NO!!! • Example: Boron is mined in Death Valley, CA. • There are two “types” of Boron. • Both have 5 p+ but one has 5 no while the other has 6no. • They are exactly alike chemically, but • different in mass.

  6. Isotopes: same number of p+, but different • number of no • -most elements have 2 stable isotopes • -EXCEPTIONS who only have 1 = Al, F, P • -Sn has 10!!!! • -Refer to an isotope by its mass number (p+ + no) • for example: uranium-238 or 238U ISOTOPES

  7. The number of p+ = ATOMIC NUMBER • represented by “Z” • if Z = 5, then the element is Boron • In the atom, what is the same as the number of p+? WHY? • p+ = e- Atoms are electrically neutral. • Hence, the number of p+ determines the identity of the element and the number of no determines the isotope of the element. - - -    Electron (-1) Atomic Number (Z) Nucleus - Proton (+1) Neutrons (0) If two elements have the same atomic number they are the same element. If two elements have different atomic numbers they are different.

  8. Dalton’s postulate now reads: • “All atoms of an element contain the same number of p+ but can contain different numbers of no.” • A particular type of atom is called a NUCLIDE (another name for isotope). • Protium, Deuterium, and Tritium are all nuclides of hydrogen. • Particles that make up the nucleus • are called NUCLEONS. • The proton and neutron are nucleons.

  9. # protons # protons + # neutrons mass number Isotopic Notation The total number of nucleons = p+ + no = mass number(“M”) Isotopic notation: X = chemical symbol M = mass # Z = atomic # X M Z

  10. Isotopic Notation

  11. Electrons lost Electrons gained

  12. Br 80 35 Symbols Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass number = 35 = 45 = 35 = 35 = 80

  13. Nd 144 60 Symbols If an element has 60 protons and 84 neutrons what is the • Atomic number • Mass number • number of electrons • Complete symbol = 60 = 144 = 60

  14. Pt 195 78 Symbols If a neutral atom of an element has 78 electrons and 117 neutrons what is the • Atomic number • Mass number • number of protons • Complete symbol = 78 = 195 = 78

  15. Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass number = 11 = 12 Na 23 1+ = 10 11 = 11 Symbols = 23 Sodium ion

  16. V 51 23 Symbols If an element has an atomic number of 23 and a mass number of 51 what is the • number of protons • number of neutrons • number of electrons = 23 = 28 = 23

  17. + - - - - - -       Metals lose electrons to form positive ions (cations): Li ---> Li+ + e- 3 p+ 3 p+ 3 e- 2 e- 4 n0 4 n0 Nucleus - Proton (+1) Neutrons (0) If # of protons > # of electrons it has a positive charge and we call it a cation.

  18. + - - - - - - - - - - - - - - - - - - - -                     Nonmetals gain electrons to form negative ions (anions): F + e- ---> F- 9 p+ 9 p+ 9 e- 10 e- 10 n0 10 n0 Nucleus - Proton (+1) Neutrons (0) If # of protons < # of electrons it has a negative charge and we call it an anion.

  19. 238 U 92 23 1+ Na 11 79 2– Se 34 27 32 24 17 20 18 25 30 18 Isotopic Notation Protons Neutrons Electrons 92 146 92 11 12 10 34 45 36 59 3+ Co 27 37 1– Cl 17 55 7+ Mn 25

  20. The p+ and no are essentially equal in mass. As you can see, the electron has very little mass when compared to both the proton and the neutron. 99.95% of an atom’s mass is found in the nucleus. Protons are over 1800 times larger than electrons. So, chemists say electrons have no mass. This is not exactly true, it’s more like they have negligible mass. Atomic Mass

  21. Actual mass (g) Relative mass Name Symbol Charge Electron e- -1 1/1840 = 0 9.109389 x 10-28 Proton p+ +1 1 1.6762623 x 10-24 Subatomic particles Neutron no 0 1 1.6749286 x 10-24

  22. (1 amu) (1 amu) (1 amu) (1 amu) (1 amu) (1 amu) (1 amu) (1 amu) (1 amu) (1 amu) (1 amu) The mass of atoms is measured in amu or (u). Amu = 1/12 the mass of the carbon-12 nuclide 1 u = 1.66054 x 10-24 g Carbon-12 is the standard. One C-12 atom has a mass of 12 u. The mass of the other elements is relative to this mass. carbon atom (12 amu) (1 amu)

  23. For carbon 1 in approximately 90 atoms are carbon-13 • The rest are carbon-12 the isotope that is 98.9% abundant. • So, for approximately 90 methane molecules…1 carbon is carbon-13 For example….Methane

  24. C-13 Where’s Waldo?

  25. He • Quarks • component of protons & neutrons • 6 types • 3 quarks = 1 proton or 1 neutron Subatomic Particles

  26. A mass spectrometer

  27. A mass spectrometer is a device that separates positive gaseous ions according to their mass-to-charge ratios. • If a stream of positive ions having equal velocities is brought into a magnetic field: • All the ions are deflected from their straight line paths into circular paths • The lightestions are deflected the most making a tighter circle • Conversely, the heaviest ions are deflected the least • A record of the separation of ions is called a mass spectrum. Mass Spectrometry

  28. Diagram of a simple mass spectrometer, showing the separation of neon isotopes

  29. The mass spectrum of neon

  30. 198 200 202 196 199 201 204 Mass spectrum of mercury vapor Photographic plate + - - Mass Spectrometry Stream of positive ions

  31. (The photographic record has been converted to a scale of relative number of atoms) The percent natural abundances for mercury isotopes are: Hg-196 0.146% Hg-198 10.02% Hg-199 16.84% Hg-200 23.13% Hg-201 13.22% Hg-202 29.80% Hg-204 6.85% 198 200 202 30 25 20 15 10 5 196 199 201 204 Mass spectrum of mercury vapor Relative number of atoms Mass Spectrum for Mercury 196 197 198 199 200 201 202 203 204 Mass number

  32. Mass spectrums reflect the abundance of naturally occurring isotopes. Natural Abundance of Common Elements Hydrogen 1H = 99.985% 2H = 0.015% 12C = 98.90% 13C = 1.10% Carbon Nitrogen 14N = 99.63% 15N = 0.37% 16O = 99.762% 17O = 0.038% 18O = 0.200% Oxygen Sulfur 32S = 95.02% 33S = 0.75% 34S = 4.21% 36S = 0.02% Chlorine 35Cl = 75.77% 37Cl = 24.23% Bromine 79Br = 50.69% 81Br = 49.31%

  33. How heavy is an atom of oxygen? • There are different kinds of oxygen atoms. • More concerned with average atomic mass. • Based on abundance of each element in nature. • Don’t use grams because the numbers would be too small Atomic Mass

  34. Abundance = Percent (% )= (part/whole) = massindividual/masswhole Average = Abundance1 (mass1) + Abundance2(mass2) + etc AVERAGE ATOMIC MASS

  35. Steps: • Multiply the mass of each isotope by its Abundance. • Add up all of the products from step 1.

  36. Example:

  37. (The photographic record has been converted to a scale of relative number of atoms) The percent natural abundances for mercury isotopes are: Hg-196 0.146% Hg-198 10.02% Hg-199 16.84% Hg-200 23.13% Hg-201 13.22% Hg-202 29.80% Hg-204 6.85% 198 200 202 30 25 20 15 10 5 196 199 201 204 Mass spectrum of mercury vapor Relative number of atoms Mass Spectrum for Mercury 196 197 198 199 200 201 202 203 204 Mass number

  38. 80 Hg 200.6 The percent natural abundances for mercury isotopes are: Hg-196 0.146% Hg-198 10.02% Hg-199 16.84% Hg-200 23.13% Hg-201 13.22% Hg-202 29.80% Hg-204 6.85% A B C D E F G (% "A")(mass "A") + (% "B")(mass "B") + (% "C")(mass "C") + (% "D")(mass "D") + (% "E")(mass "E") + (% F)(mass F) + (% G)(mass G) = AAM (0.00146)(196) + (0.1002)(198) + (0.1684)(199) + (0.2313)(200) + (0.1322)(201) + (0.2980)(202) + (0.0685)(204) = x 0.28616 + 19.8396 + 33.5116 + 46.2600 + 26.5722 + 60.1960 + 13.974 = x x = 200.63956 amu

  39. Chlorine has two naturally occurring isotopes, 35Cl (34.9689 amu) and 37Cl (36.9659 amu). If chlorine has an atomic mass of 35.4527 amu, what is the percent abundance of each chlorine isotope? What must be the total abundance of chlorine? What is this percentage written as a decimal? If we designate the abundance of the first isotope as x, what MUSTbe the abundance of the other isotope? Example

  40. Abundance1 (mass1) + Abundance2(mass2) + etc = Average Atomic mass 24.226 % Cl-37 75.774 % Cl-35

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