• Electron affinity - energy required to place an
electron on a gaseous atom, forming an
• The attraction of an atom for an electron
• Electron affinities may have positive or negative
• Negative values - energy released
• Positive values - energy absorbed
Energy change accompanying addition of
electron to gaseous atom:
Cl + e− Cl−
Trends in Electron Affinity
• In general, electron
affinity becomes more
exothermic as you go
from left to right across a
• The greater the attraction
between a given atom
and an added
electron, the more
negative the atom’s
electron affinity will be.
Electron affinities increase (numerical value
becomes more negative) from left to right for a
period and bottom to top for a group.
The greater (more negative) the electron
affinity, the more stable the anion will be.
Electronegativity and Bond Polarity
• Bonding between the two ends of the bonding
continuum, ionic and covalent bonding, is described
using electronegativity and bond polarity.
• Electronegativity is the attraction of an atom for the
shared electrons in a covalent bond.
– Electronegativities are not measured quantities.
– Electronegativities are assigned based on factors such as
atomic size, electron affinity, and ionization energy.
– The higher the electronegativity value, the more likely an
element will attract extra electron density during
• Electronegativities increase from left to right across a
period and from bottom to top for a group.
• Fluorine is the most electronegative element, with an
electronegativity of 4.0.
• The ability of atoms in a
molecule to attract
electrons to itself.
• On the periodic
increases as you go…
– …from left to right across
– …from the bottom to the
top of a column.
A particular slide catching your eye?
Clipping is a handy way to collect important slides you want to go back to later.