Atomic Variation
Ionization energy, Atomic Radius,
Electronegativity and Electron affinity
Atomic Radii and Volume
• Atomic size indicated by radius of atom
• Atomic radius helps determine properties of
an element (bp, mp, density)
• Within ONE PERIOD atomic radius decreases
as atomic number increases
– b/c the increased positive charge in the nucleus
attracts electrons more strongly including those in
outer shells
– Electrons are pulled in, atomic radius decreases
• Within A GROUP atomic radius increases with
atomic number
– Number of electron shells increases by one for
each new period
– Increase in volume from new shell in more
influential than the decrease in volume caused by
the additional nuclear charge
– There is a net increase in atomic radius
decreases
increases
Ionization Energy (IE)
• Electrons with lots of energy can be used as
“projectiles” to knock electrons out of an atom
• Positive ions = atoms that have lost electrons
• Ion = electrically charged atom (+ or -)
• 1st ionization energy: minimum amount of energy
required to remove the least tightly held electron
from an atom in the gaseous state
– as energy increases, most easily removed electron will
be knocked off first
• 2nd ionization energy: amount of energy
needed to remove the 2nd least tightly held
electron
• removal of successive electrons from the atom
gets harder and ionization energies get larger
• Ionization energy increases as you move
towards the noble gases (left to right) but not
regularly (it’s a trend)
• IE follows the increasing positive nuclear
charge
• Increased nuclear charge within the period
attracts all electrons within the atom more
strongly and it becomes harder to remove
electrons (ionization energy increases)
• In group 1, there are LOW ionization energies,
group 18 has very high ionization energies
• Moving down within a family, ionization
energy tends to decrease
• The progressive increase in positive nuclear
charge top to bottom SHOULD cause an increase
in IE because the nucleus will exert a greater
attraction on the surrounding electrons
• What actually occurs is that each move down an
energy level in the group, the outermost
electrons are one shell farther from the nucleus
and are “screened” from the positive nuclear
charge by the inner shell electrons: net result the
IE decreases
• On the right, IE decreases because of the
screening effect due to the extra electrons being
more influential than the increased positive
nuclear charge
Electronegativity
• The measure of the tendency of an atom or group of
atoms to attract electrons when forming covalent
bonds
• As one moves from the left to right within a period, the
radius of the atom decreases and thus there is a
stronger attraction for electrons and electronegativity
increases
• As one moves from the bottom to the top of a family,
the electrons are closer to the nucleus and thus there
is a stronger attraction for electrons and the
electronegativity increases
• .
Summary
• Atomic size
increases
• Ionization energy
• Electronegativity
Electron Affinity
• The energy that is released when a negative ion is formed by adding
an electron an atom
energy increases = electron affinity increases
F (g) + e-  F-1 (g) + energy
• A large value for IONIZATION energy indicates that the removal of
an electron is difficult and the formation of a positive ion is unlikely
to occur
Na + energy (IE)  Na+1 + 1 e-
• A large value for electron affinity indicates that much energy is
released when a negative ion is formed by the addition of an
electron and that such a process is very likely to occur
F (g) + e-  F-1 (g) + energy (electron affinity)
Homework
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Periodic table quiz!
p. 36-41 supplement notes
p. 41 #1-5, 7, 8, 10
p. 73 #1,2