Electron Configurations for the
Ions of Transition Metals & Main
Group Elements
Chemistry 11
The Order of Orbital “Filling”
1. Lowest energy to higher energy.
2. Adding electrons can change the energy of
the orbital.
3. Half filled orbitals have a lower energy.
4. Makes them more stable.
5. Changes the filling order
Practice: Writing Electron Configurations
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Titanium - 22 electrons
1s22s22p63s23p64s23d2
Vanadium - 23 electrons
1s22s22p63s23p64s23d3
Chromium - 24 electrons
1s22s22p63s23p64s23d4 is expected
But this is wrong!! Why?
True Configuration of Chromium
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1s22s22p63s23p64s13d5
Why?
This gives us two half filled orbitals.
Slightly lower in energy.
The same principal applies to copper.
Copper’s Electron Configuration
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Copper has 29 electrons so we expect
1s22s22p63s23p64s23d9
But the actual configuration is
1s22s22p63s23p64s13d10
This gives one filled orbital and one half filled
orbital.
Remember these exceptions
Valence Electrons
Are the electrons in the highest occupied energy level
of an element’s atom.
 Are usually the only electrons used in the formation of
chemical bonds.
Note:
Many of the similar chemical properties of elements
in the same group (vertical column) are related to the
number of “s” and “p” electrons in the highest
occupied energy level. These electrons are valence
electrons.
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Example 1: Sodium
 11Na
 1s22s22p63s1
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Highest energy level = 3
Single “s” electron
No “p” electrons for this element
Na has 1 valence electron
Ion:
Example 2: Phosphorus
 15P
 1s22s22p63s2 3p3
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Highest energy level = 3
Two “s” electrons
Three “p” electrons
5 valence electrons
Ion:
Example 3: Potassium
 19K
Electron Configurations
 1s22s22p63s2 3p6 4s1
 Highest energy level = 4
 1 valence electron
 Ion:
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Example 4: Carbon
 6C
Electron Configuration
 1s22s22p2
 Highest energy level = 2
 4 valence electrons
 Ion:
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Example 5: Magnesium
 12Mg
Electron Configuration
 1s22s22p63s2
 Highest energy level = 3
 2 valence electrons
 Ion:
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Example 6: Oxygen
 8O
Electron Configuration
 1s22s22p4
 Highest energy level = 2
 6 valence electrons
 Ion:
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Transition Metals
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Do not form ions with noble gas configurations
If they did, they would have to lose 4 or more
electrons, and the energy needed to do this
would be too high.
These metals do form cations (“+” charged ion)
with more than one charge (multi-valent)
Electrons are first moved from the outer “s” and
then inner “d” sublevels.
Example 1:
 25Mn
 Mn2+
(18Ar)4s23d5
loses 2 electrons from the “s”
sublevel
 Mn2+
(18Ar)4s03d5
Example 2:
 26Fe
 Fe2+
(18Ar)4s23d6
loses 2 electrons from the “s”
sublevel
 Fe2+
(18Ar)4s03d6
 Fe3+
(18Ar)4s03d5
Question 1
Read the following electron configurations to
determine the identities of the following
elements:
a) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2
b) 1s2 2s2 2p6 3s2 3p3
c) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6
6s2 4f 5d10 6p6
d) 1s2 2s2 2p2
e) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5
Question 2
Explain what is meant by the term
“isoelectronic”.
Answer:
The prefix “iso” means “the same”, so
isoelectronic means that two atoms or ions have
the same number of electrons or the same
electron configuration.
Question 3
What are four ions, with their charges, that are
isoelectronic with each of the following:
a) neon: N3– O2– F1– Na1+ Mg2+ Al3+
b) argon: P3– S2– Cl1– K1+ Ca2+
Sc3+
c) krypton: As3– Se2– Br1– Rb1+ Sr2+
Y3+
d) an S2– ion: P3– Cl1– K1+ Ca2+ Sc3+
Question 4
A calcium ion, Ca2+ , is isoelectronic with argon. Does this
mean that calcium has “turned into” argon?
Explain.
Answer:
No, calcium has not turned into Argon. Remember, it is the
atomic number (number of protons) that determines what type
of element an atom is. The calcium ion has the same number
of electrons as an Argon atom. This just means that they are
Both stable octet with 18 electrons.
Question 5
Write the electron configuration for the
element with atomic number 117. In which
chemical group does it belong? Predict the
charge on the ion that it will form.
Question 5
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2 5f14 6d10 7p5
This element belongs to the Halogen family or
Group 17 (VIIB). It will gain one electron to have
the same configuration as a Noble Gas, so it will
form ions with a charge of 1-.