Electron Configurations of atoms and ions
Introduction:
Metals tend to have relatively low ionization energies. Thus, they generally lose electrons
readily. Loss of electrons by a metal atom produces a positively charged ion called a cation.
The electrical charge of a metal cation depends on the number of electrons the metal loses.
When they form cations, the group 1,2 and 3, 4 metals usually lose their valence electrons. The
valence electrons of these groups are in the s and p sublevels. Upon producing a cation, these
metals end up with positive charges (oxidation numbers) +1 group 1, +2 group 2, etc. Upon
losing all its valence electrons, the metal cation generally has the stable outer electron
configuration of a noble gas. For example when potassium becomes +1 charged its electron
configuration is the same as argon, with 18 electrons.
Nonmetals have relatively high ionization energies, so they tend not to lose electrons. Instead
they gain electrons to produce negative anions. They generally gain just enough electrons to
attain the stable electron configuration of a noble gas, or eight outer energy level electrons in
their highest occupied s and p orbitals. For example bromine will gain one more electron (-1
charge) to have 36 electrons, just like Kr, a noble gas.
In general, to write the electron configuration of any cation or anion, write the electron
configuration for the atom and add or subtract the required number of electrons.
Transition metals also lose electrons to produce cations. Unlike most representative metals, the
number of electrons that can be lost by transitions metals can vary. Iron for example, can for the
iron +3 ion and the +2 ion, by losing three or two electrons. In general, transition metals lose
their outer s orbital electrons before they lose their outer d orbital elect6rons. This explains why
many transitions metals produce cations that carry a +2 charge. Transition metals ions can have
higher charges by losing one or more electrons form their d orbitals. Transition metal ions
having partially filled d orbital electron configurations usually have a color. Metal cations that
have no d electrons or completely full d orbitals usually are not colored.
Purpose:
In this experiment you will observe a variety of chemical solutions containing common cations
and anions. You will write electron configurations for many of the ions contained in the
solutions. You will observe colored solutions and draw conclusions about the electron
configurations of the metals ions in the colored solutions.
Procedure:
1. To each well containing 1 drop of a solution listed below add 2 drops of NaOH. Then
record your observations. Repeat the experiment by adding 2 drops of Na3PO4. Repeat
the experiment again by adding 2 drops Na2CO3.
2. These are the solutions mentioned in procedure #1 NaCl, MgSO4, AlCl3, FeCl3, CaCl2,
NiSO4, CuSO4, ZnCl2, AgNO3.
Make a Data Table to record your observations, pay close attention to the colors of the
reactants and products.
NaCl
w/NaOH
MgSO4
w/NaOH
AlCl3
w/NaOH
w/Na3PO4
w/Na3PO4
w/Na3PO4
w/Na2CO3
w/Na2CO3
w/Na2CO3
FeCl3
w/NaOH
CaCl2
w/NaOH
NiSO4
w/NaOH
w/Na3PO4
w/Na3PO4
w/Na3PO4
w/Na2CO3
w/Na2CO3
w/Na2CO3
CuSO4
w/NaOH
ZnCl2
w/NaOH
AgNO3
w/NaOH
w/Na3PO4
w/Na3PO4
w/Na3PO4
w/Na2CO3
w/Na2CO3
w/Na2CO3
Questions for the electron configuration lab:
1. Write the electron configurations for Na, Mg, and Al.
2. Write the electron configurations for Na+1, Mg+2, and Al+3. What do they all have in
common?
3. Write the electron configurations for Cl and Cl-1.
4. Transition metals with partially filled d orbitals usually have a color. Based on your
observations, which solutions contain transition metal ions with partially filled d orbitals?
5. Transition metals usually lose s orbitals first and then d electrons when they produce
ions. Write the electron configurations for Fe and Fe+3 and Ni and Ni+2.
6. The solution Zn +2 ions is not colored. What does this suggest about its electron
configuration? Write the electron configuration of Zn and Zn+2.
7. Predict which of the following transition metal ions has a color: Cr+3, Cd+2, Hg+2, and
V+2. Explain your answers.
8. Do the colored precipitates all contain transition metal ions with partially filled d
orbitals?
9. Which metal cations in the experiment formed colored precipitates with Na2CO3? Why?
10. Which metal cations in the experiment formed colored precipitates with Na3PO4?
Why?