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Unformatted text preview: CHEM 130 Exp. 8: Molecular Models In this lab, we will learn and practice predicting molecular structures from molecular formulas. The Periodic Table of the Elements IA VIIIA 1 H IIA IIIA IVA VA VIA VIIA 2 He 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57-71 La series 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89-103 Ac series 57 La 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu 89 Ac 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 100 Fm 101 Md 102 No 103 Lr Part I: Valence Electrons To draw a Lewis Structure, we must know how many valence electrons each atom possesses. For main group atoms, we can get this information by looking at the periodic table. Rule 1: A main group atom has a number of valence electrons equal to the position of its main group column from the left of the periodic table (first main group column has one valence electron, second main group column has two valence electrons, etc.). Example: Lithium (Li) is in the first column, so it has one valence electron. The columns of the periodic table are often labeled at the top with a number. This number is called the group number, and is written in roman numerals. Rule 2: A main group atom will have a number of valence electrons equal to its group number. Determining the number of valence electrons for transition metal, lanthanide, and actinide atoms is much more complicated because of the d and f orbitals. In this course, we will confine ourselves to main group atoms, and we will ignore electrons in d and f orbital when counting valence electrons. Exercise 1: Complete the first column only of Table 1 by writing the number of valence electrons in each of the atoms listed. Part II: Electron Dot Pictures We can write an abbreviated picture of a main group atom with its valence electrons by using the atomic symbol surrounded by dots. An example for neon is shown below. Ne Neon has 8 valence electrons, so we surround the atomic symbol for neon (Ne) with 8 dots. Notice that the dots are written in pairs at four positions around the symbol: right, left, bottom, and top. Rule 3: When writing the electron dot picture of an atom, add one electron dot to all four positions before adding a second electron dot to any positions....
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