Nitrogen Electrical Structure
Nitrogen has a high electronegativity, meaning that it
strongly attracts electrons. This makes sense, since it has a
significant nuclear charge, very little screening, and a small radius.
Nitrogen also has electron affinity > 0, meaning that it does not
attract electrons. This makes sense, since an electron added to a
nitrogen atom will be paired with another electron in a p-orbital,
resulting in more repulsion in a small atom and therefore, a less
stable atom after the addition of the electron.
So, how is it that nitrogen both attracts electrons (high
electronegativity) and does not attract electrons (E.A. > 0)?
Electronegativity, or EN
(the relative tendency of an element's atoms to attract
valence electrons) is related both to the size of
the element's atomic electron affinity, or EA (energy liberated
when an extra electron attaches to a single neutral atom)
and its first ionization energy, or IE
(energy required to remove an existing valence electrons from the
After Pauling's work, Robert Millikan
proposed the following formula for EN:
EN(atom) = constant*(|EA| + |IE|)/2
When the right value for (constant) is chosen, this produces
electronegativities in reasonable (but not perfect)
agreement with Pauling's original scale
(which is derived from bond energies).
So in this way of thinking, an atoms EN has
a contribution due to its tendency to hold onto its
own valence electrons (manifested in IE) and also its
tendency to accept other atom's valence electrons (manifested
In this case, although N has low EA, it has high enough IE for it to
have reasonably high EN. F has large EA and IE. C has a larger
EA than N but its IE is so much smaller that C ends up having lower EN
EN is a somewhat controversial concept and there are a
number of EN scales that have been developed since Pauling's
original work. EN is not as fundamental a quantity
as EA or IE, both of which be can directly measured by experiment.
However, EN is a very useful concept as long as you use it
simply as a helpful organizing principle for certain chemical
hope this helps!
There are a number of issues here that you need to distinguish:
1. Electron affinity is the ENERGY RELEASED when an atom in the gas
phase adds an electron to form a negative ion: E + e(-1) ---> E(-1). In some
cases this can be measured experimentally; in other cases it is calculated.
2. Unfortunately, even though most electron affinities are EXOTHERMIC,
historically these are tabulated as positive quantities, which is the
opposite the normal sign convention that exothermic reactions have a
negative value. Electron affinity is a property of ATOMS IN THE GAS PHASE.
3. In contrast to electron affinity, ELECTRONEGATIVITY is an empirical
scale of the ability of an atom IN A COVALENTLY BONDED MOLECULE to attract
electrons. This is quite a different matter than electron affinity. Linus
Pauling first introduced this concept (See: "General Chemistry" by Linus
Pauling) but other empirical scales have been suggested by other authors.
(See: "Inorganic Chemistry" by James E. Huheey, for example). Any text on
inorganic chemistry will discuss electronegativity in detail as well.
One needs to be cautious in applying any of these empirical relations
too strictly. They are empirical and show trends.
Click here to return to the Chemistry Archives
Update: June 2012