The Periodic Table and Ionic
Bonding:
Part 5-Periodic Table Trends
1
Objectives
• -Describe what electron affinity is
and how it is related to ion formation
• -Explain how trends in electron
affinity are shown in the periodic
table
2
Periodic Trend #4:
Electron Affinity (E.A)
• Electron affinity- energy released when an
atom gains an electron and the higher it is the
greater attraction an atom had for it
General Formula
X (atom) + electron ---> X-1 (ion) + energy
Specific Formula
Cl
+ electron ---> Cl-1 + 83.4 kcal/mole
• Negative ion with 1 more electron than proton
• A negative ion = anion
• Larger than the original atoms
Periodic Trend #4:
Electron Affinity (E.A)
• ACROSS PERIODS electron affinity
INCREASES to a maximum in Group VII
then is a minimum in Group VIII
ATOM: Na
-> Cl
Ar
E.A.:
12.6
-> 83.4 -8.5 (kcal/mole)
• DOWN GROUPS electron affinity usually
DECREASES due to the positive nucleus
being less attracted to the electrons
further away
Periodic Trend #4:
Electron Affinity (E.A)
• Nonmetals will gain enough electrons to have a
stable electron structure like a noble gas or core
atom (s2p6)
•
Group VII atoms (s2p5) gain 1 electron & form -1
ions
• Group VI atoms (s2p4)gain 2 electrons & form -2
ions
• Group V atoms s2p3)gain 3 electrons & form -3
ions
Periodic Trend #4:
Electron Affinity (E.A)
Atom e configuration Ion e configuration
Cl 1s22s22p63s23p5 Cl-1
1s22s22p63s23p6
S 1s22s22p63s23p4 S-2
1s22s22p63s23p6
P 1s22s22p63s23p3 P-3
1s22s22p63s23p6
not stable
stable [Ar]
Ion Summary
GROUP
I
II
III
IV
V
VI
VII
VIII
Electron
Configuration s1
Ends in:
s2
s2p1
s2p2
s2p3
s2p4
s2p5
s2p6
Electrons
Lost
1
2
3
-
-
-
-
-
Electrons
Gained
-
-
-
-
3
2
1
-
Ion Formed
+1
+2
+3
-
-3
-2
-1
-
Remember that the group number tells you how many valen
electrons there are!!!
*Note – there are some exceptions to this chart!
8
Exceptions
• The elements in this
table can form more
than one type of ion
• When naming
these compounds,
the type of ion is
expressed in the
name with a roman
numeral
• These are all transition
elements and they can
form a variety of ions!
Exceptional
elements
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Relating IE, EA and Metallic
Properties
• High in metallic properties = low
ionization energy = low electron
affinity
• Low in metallic properties = high
ionization energy = high electron
affinity
*Note – there are some exceptions
Objectives
• -Describe what electron affinity is
and how it is related to ion formation
• -Explain how trends in electron
affinity are shown in the periodic
table
11