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Valence Electrons &
Configurations for Ions
 Valence Electrons
 Main group elements
 Transition metals
 Electron configuration
for Ions
 Main group ions
 Transition metal ions
Valence Electrons for P
 Which are the valence electrons in a
phosphorus atom?
Periodic Table
Valence Electrons
 For main group elements
(s and p blocks)
 Valence electrons occupy
orbitals in the valence shell
(largest n).
 Which are the valence
electrons in Br?
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Valence Electrons
for Main-Group Elements
Period 4 Main-Group Elements








K
Ca
Ga
Ge
As
Se
Br
Kr
[Ar] 4s1
[Ar] 4s2
[Ar] 4s2 3d10 4p1
[Ar] 4s2 3d10 4p2
[Ar] 4s2 3d10 4p3
[Ar] 4s2 3d10 4p4
[Ar] 4s2 3d10 4p5
[Ar] 4s2 3d10 4p6
Group IA
Group IIA
Group IIIA
Group IVA
Group VA
Group VIA
Group VIIA
Group VIIIA
Practice
 Use a periodic table to determine the number of
valence electrons in an atom of each element:
a) Li
b) Si
c) Ga
d) As
e) Pb
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Periodic Table
Valence Electrons for
Transition Metals
 The valence electrons for transition metals
(B elements) are determined differently than
for main-group elements (A elements).
 For transition metals, the s and d electrons are
valence electrons even though the d electrons are
in a lower principal energy level.
 Example: Fe:
[Ar] 4s2 3d6
Valence Electrons for
Transition Metals
Electron Configurations
for Ions
 Some Exceptions to Transition Metal
Electron Configurations:
Main Group Elements:
Group 6
Group 11
3d5
Cu: [Ar] 4s1 3d10
Mo: [Kr] 5s1 4d5
Ag: [Kr] 5s1 4d10
Cr: [Ar]
4s1
 What is the trend?
 Al

S

Electron Configurations
for Ions
Transition metals lose their highest n
value s electrons first:
 Ti
 Ti2+
 Ti4+
[Ar] 4s2 3d2
[Ar] 4s0 3d2 = [Ar] 3d2
[Ar] 4s0 3d0 = [Ar]
Al3+
S2
1s2 2s2 2p6 3s2 3p1
1s2 2s2 2p6
[Ne] 3s2 3p4
[Ne] 3s2 3p6= [Ar]
Electron Configurations
for Ions
What is the electron configuration for
these ions of tin and zinc?
Sn
[Kr] 5s2 4d10 5p2
Sn2+
Zn
[Ar] 4s2 3d10
Zn2+
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Valence electrons and
Ions
Valence electrons are most easily
removed from an atom, so they are
important in chemical properties such as
ion formation and other chemical
reactions.
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