Trends in Electronegativity

Chemistry

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Pauling scale

Linus Pauling was the original scientist to describe the phenomena of electronegativity. The best way to describe his method is to look at a hypothetical molecule that we will call XY. By comparing the measured X-Y bond energy with the theoretical X-Y bond energy (computed as the average of the X-X bond energy and the Y-Y bond energy), we can describe the relative affinities of these two atoms with respect to each other.

Bond Energies = (X-Y)measured - (X-Y)expected

 if the electonegativities of X and y are the same, then we would expect the measured bond energy to equal the theoretical (expected) bond energy and therefore the bond energies would be zero. If the electronegativities of these atoms are not the same, we would see a polar molecule where one atom would start to pull electron density toward itself, causing it to become partially negative.By doing some careful experiments and calculations, Pauling came up with a slightly more sophisticated equation for the relative electronegativities of two atoms in a molecule:

 EN(X) - EN(Y) = 0.102 (1/2).1 

In that equation, the factor 0.102 is simply a conversion factor between kJ and eV to keep the units consistent with bond energies.

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Electronegativity

The tendency of an atom to attract electrons to itself when combined in a compound is known as electronegativity. The factors which affect the electronegativity are atomic size and nuclear charge. As atomic radii increases, electronegativity decreases. As nuclear charge increases, electronegativity increases. Electronegativity decreases down a group and increases across a period.

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Applications of electronegativity

The concept of electronegativity is very useful in predicting metallic, non-metallic characters of elements and polarity of bonds.

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Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. 

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Factors which affect electronegativity

Factors Affecting Electronegativity
  • Nuclear charge. The higher the nuclear charge, more will be the electronegativity value of an element, since the nucleus will be able to attract or pull more electrons towards itself.
  • Atomic size
  • Screening effect or shielding effect.

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Trends in electronegativity across a period from left to right

Trend-wise, as one moves from left to right across a period in the periodic table, the electronegativity increases.

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