Electron affinity chemistry engineering ppt

Chemistry

1. Electron
Affinity

2. is defined as the energy
process in which an
electron is acquired by the
atom in the gas phase
Electron affinity...

3. More info...
•The larger the affinity of an atom
for an electron, the more negative
the value
• Electron affinity trends are related
to the trends of ionization energy
because both represent the energy
involved in the gain or loss of an
electron by an atom, respectively

4. The trend down the column...
Electron affinity
decreases as it
goes down a column

5. This is because...
•Electrons are added increasingly
farther from the nucleus, so the
attractive force between the nucleus
and electrons decreases
•The outer electrons experience less
of a positive charge as you go up the
periodic table (effective nuclear
charge)

6. The trend across a period...
Electron affinity
increases as it
goes across a period

7. This is because...
•The octet rule states that atoms
with close to full valence shells will
tend to gain electrons. When they
gain the electrons, they use energy,
which allows the ion to become more
stable
•The outer electrons experience less
of a positive charge as you go across
a period (effective nuclear charge)

9. Units of EA
KJ/Mol
** electron affinity is negative

10. Exceptions...
•Nitrogen atoms have no affinity
- in N
-
ions, electron-electron repulsion
makes these ions unstable
•Beryllium anion has no affinity
- Be
-
is not stable, because the added
electron is assigned to a higher energy
subshell (2p) than the valence electrons
(2s)

11. More Exceptions...
•Noble gases have no affinity
- they have full valence shells and by
adding or taking away electrons, they
become unstable
•Fluorine has a low affinity
- because it has a small amount of
shells and when you add another
electron, electron-electron repulsion
happens, creating an unstable ion