Relative Size
Ionization Energy
Electron Affinity
Electronegativity
General Rule - Relative Size
 When looking at the periodic
table, atoms get bigger:
Top to bottom
Right to left
http://www.lung-cancer-report.com/berylliosis-beryllium/picture-of-beryllium-atom.html
Top to Bottom
Down a Column
The atoms get bigger because
the electrons are in
a higher energy level.
Left to Right
Across a Row
The atoms get smaller because the
positive charge in the middle of
the atom is more concentrated so
it’s sucking the electrons in closer.
Relative Size Chart
http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/atomic-radii.html
*Positive Ions and
Negative Ions*
 Positive Ions: If an atom loses all
of its valence (outermost)
electrons, it’s going down to the
next energy level so it’s getting
smaller.
 Losing electrons = positive charge
 More protons than electrons = +
charge
*Positive Ions and
Negative Ions*
 Negative Ions: If an atom gains
electrons it has a negative charge.
The nucleus stays the same but the
radius gets bigger because there
are more electrons.
 Gaining electrons = negative charge
 More electrons than protons = charge
Sample Problems - Part 1
Which one has a larger radius?
(a) Ti or Ni
(b) F or F-1
(c) Ba or Hf
(d) Ca or Ca+2
Sample Problems - Part 2
Which one has a smaller radius?
(a) K or Cs
(b) Cs or Os
(c) O or O-2
(d) Na or Na+1
Challenge
Excluding the Noble Gases because
they’re special:
What is the smallest atom?
____________________
What is the largest atom?
____________________
Ionization Energy
Definition: The energy required to remove an
electron from an atom.
First Ionization Energy
 The energy needed to remove the most
loosely held electron from an atom.
 Measured in kilojoules per mole (kj/mol).
General Rule Ionization Energy
 Ionization Energy increases going
across periods (rows) - increases as
atomic number increases.
 Ionization Energy decreases going down
groups (columns).
Classifying Elements based on
Ionization Energy
 Metals
 Tend to lose electrons to become more
stable
 Low ionization energy
•Nonmetals
•Tend to gain electrons to become more stable
•High ionization energy
Noble Gases
Have an octet so they’re already stable
Very high ionization energy
Electron Affinity
Definition: the attraction of an atom for an
additional electron
 Metals tend to have low electron affinities.
 Nonmetals tend to have high electron
affinities.
Sample Problems - Part 3
 Which one has a lower ionization energy?
(a) Cl or Kr
(b) Iron or Iodine
 Which one has a higher electron affinity?
(a) Oxygen or Barium
(b) Na or Cl
Electronegativity
Definition: the relative attraction of an atom
for a shared pair of electrons.
 The difference in electronegativities
increases as the bond strength between two
atoms increases.
• Metals tend to have low electronegativities.
• Nonmetals tend to have high
electronegativities.
Electronegativity Chart
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www.monroecc.edu/wusers/flanzafame/PerElNegativity.pdf
Sample Problems - Part 4
 Which atom has a higher electronegativity?
(a) Ca or C
(b) Titanium or Tellurium
 Which atom has a lower electronegativity?
(a) Br or Be
(b) Strontium or Selenium
Factors that affect
Ionization Energy,
Electron Affinity, and
Electronegativity
1. Distance from nucleus
2. Stability
Connections between
Ionization Energy,
Electron Affinity, and
Electronegativity



In general, as Electron Affinity increases,
Ionization Energy increases.
Electron Affinity and Electronegativity
increase going across a period (left to
right).
Ionization Energy and Electronegativity
increase going up a column (bottom to top).