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C6H12O6 + O2 ->CO2 +H2O Using this equation, which of the following are the reactants?
f
An issue with ionization potential and electron affinity is that they are defined and measured as reactions in the gas phase. Although values have been determined for molecular fragments it is still difficult to correlate with reaction trends in solution. To overcome this issue the concept of electronegativity was developed.
Electronegativity is defined as the tendency of an atom in a molecule to attract electrons to itself . Although several electronegativity scales have been developed, that by Linus Pauling ( [link] ) is the most often used. [link] provides selected Pauling electronegativity values (unit less).
| Element | Pauling scale |
| F | 4.0 |
| O | 3.5 |
| Cl | 3.0 |
| N | 3.0 |
| S | 2.5 |
| C | 2.5 |
| H | 2.1 |
| B | 2.0 |
| Na | 0.9 |
The advantage of the Pauling electronegativity scale is that it allows the prediction of general behavior. When comparing electronegitivity values between two atoms, the larger the value, the stronger the "pull" on the electrons and the more "ionic character" the interaction or bond will possess. For example, let's compare the electronegativity of O (3.5) and H (2.1).Because O has a higher electronegativity, O will tend to "pull" the electrons from H, this gives rise to a slight but significant negative charge around the O atom due to the higher tendency of the electrons to be associated with the O atom. It therefore gives a slight positive charge to the H atom due to the decrease in the probability of finding an electron near by. It is electronegativity, the tendency to attract electrons that gives rise to the concept of polarity and dipole . Thus, a H-O bond (3.5 - 2.1 = 1.4) is more polar than a H-S bond (2.5 – 2.1 = 0.4).
Finally, we can use the periodic table to get a general idea as to the strength or weakness of an atoms electronegativity. Those atoms with the strongest electronegativity tend to reside int he upper right hand corner of the table, such as fluorine (F), oxygen (O) and Chlorine (Cl); while the lowest electronegativity tend to be found at the other end of the table, in the lower left, such as francium (Fr, 0.7), cesium (Cs, 0.79) and radium (Ra, 0.89). More information on electronegativity can be found at the UC Davis chemwiki site: UC Davis Chemwiki Electronegativity
Using a periodic table, electronegativity increases as
c
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