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Lesson02 - The Elements of Organic Chemistry 100 Cl P S O...

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0% 20% 40% 60% 80% 100% crude petroleum dry nonvascular plant tissue (bacteria) dry vascular plant tissue (woody anglosperm) dry human muscle tissue Other Cl Ca K S P Mg Na O N C H The Elements of Organic Chemistry The elemental abundance (weight percent) of crude petroleum and dry tissue from living matter. The major elements are carbon, hydrogen, nitrogen and oxygen. Sources: The Chemistry and Technology of Petroleum , Speight 1999 3rd ED. p. 217 Environmental Chemistry of the Elements, Bowen 1979 pp. 88-90, pp. 92-93, pp. 103-104 H H H H C C C C S N N N O O O P Cl K
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Organic Chemistry: A Period 2 Science The red diamonds indicate those elements most important in organic chemistry. The yellow squares are elements also found in common organic structures.
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van der Waals Radii Atomic numbe r Element Van der Waals radii (Å) 1 H 1.20 6 C 1.70 7 N 1.55 8 O 1.52 9 F 1.47 14 Si 2.10 15 P 1.80 16 S 1.80 17 Cl 1.75 35 Br 1.85 53 I 1.98 Relative Size of Some Neutral Elements 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9 10 11 The relative sizes of the neutral atoms are shown as a function of their position within the periodic table. Within a given row, the atoms get smaller as the atomic number increases. Within a given column, the atoms get larger as the atomic number increases. C Si N O F H P S Cl Br I http://periodictable.com/Properties/A/VanDerWaalsRadius.v.html
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Stability Trends for Negative Charge Ability to Stabilize Negative Charge For atoms in the same row , stability is determined by electrognegativity (the larger the electronegativity, the greater the stability). For atoms in the same column , stability is determined by size (the larger the size, the greater the stability). What’s the rationale behind these rules? Within a row, the stability trends with electronegativity as expected. However, within a column, stability trend runs counter to electronegativity because size dominates (within a row atomic sizes are similar but between rows the atomic size varies significantly). Here’s why size matters. The valence electron cloud carries the net negative charge. The more this charge cloud is spread out (i.e., the lower the charge density), the greater the stability. Thus, the anion with the largest size (iodide) is most effective at accomplishing this task. C H H H N H H O H methyl anion amide hydroxide F fluoride Of the anions listed above, we are all familiar with hydroxide ion, so we will use this as our reference. Although me may think of hydroxide as a fairly strong base, it turns out to be far less basic than the nitrogen or carbon atoms that bear a formal charge of -1. Why? The rules state that within a row of the periodic table, the stability of negative charge tracks with electronegativity.
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