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Minggu, 08 Agustus 2010


Methane has four covalent C-H bonds. Because all four bonds have the same length and all the bond angles are the same (109.5°),we can conclude that the four C-H bonds in methane are identical.
The potential map of methane shows that neither carbon nor hydrogen carries much of a charge: There are neither red areas, representing partially negatively charged atoms, nor blue areas, representing partially positively charged atoms. The absence of partially charged atoms can be explained by the similar electronegativities of carbon and hydrogen, which cause carbon and hydrogen to share their bonding electrons relatively equally. Methane is a nonpolar molecule.
You may be surprised to learn that carbon forms four covalent bonds since you know that carbon has only two unpaired electrons in its ground-state electronic configuration. But if carbon were to form only two covalent bonds, it would not complete its octet. Now we need to come up with an explanation that accounts for carbon’s forming four covalent bonds. If one of the electrons in the 2s orbital were promoted into the empty 2p atomic orbital, the new electronic configuration would have four unpaired electrons; thus, four covalent bonds could be formed.
Because a p orbital is higher in energy than an s orbital, promotion of an electron from an s orbital to a p orbital requires energy. The amount of energy required is 96 kcal/mol. The formation of four C-H bonds releases 402 kcal/mol of energy because the bond dissociation energy of a single C-H bond is 105 kcal/mol If the electron were not promoted, carbon could form only two covalent bonds, which would release only 201 kcal/mol So, by spending 96 kcal/mol (or 402 Kj/mol) to promote an electron, an extra (or 879 kJ/mol) is released. In other words, promotion is energetically advantageous.

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2 komentar:

  1. ada bahasa indonesia gak, soalx gw gk ngerti nih,gw btuh bnget artikelnya, tQ....

  2. kan ada tranlator d samping kiri tuh