Video Transcript
Which of the following electronic
configurations correctly corresponds to the titanium two plus ion? (A) Brackets Ar 4s2, (B) brackets
Ar 3d1 4s1, (C) brackets Ar 3d2 4s2, (D) brackets Ar 3d2, (E) brackets Ar.
Electronic configurations describe
how many electrons an atom or ion has and how these electrons are arranged in
electron shells and subshells. There are s, p, d, and f subshells,
and the letter tells us which type of atomic orbitals the subshell contains. The periodic table can be divided
into blocks which represent these subshells. In this video, we will not be
concerned with elements in the f block.
Titanium is a transition metal
located in period four and group four of the periodic table, and we can see that it
is located in the d block. The atomic number of titanium is
22. This means that a titanium atom has
22 protons. Since neutral atoms contain the
same number of protons and electrons, a titanium atom also has 22 electrons.
To begin writing an electronic
configuration, we will need to make use of the aufbau principle. The aufbau principle states that
electrons fill the lowest-energy subshells before they fill higher-energy ones. The subshells on the periodic table
are in order of increasing energy. When writing the electronic
configuration, each subshell label has a coefficient, which is the principal quantum
number 𝑛 and represents the energy level. The letter represents the type of
subshell. Finally, the superscript represents
the number of electrons in the subshell.
It’s important to remember that all
s subshells can hold a maximum of two electrons. d subshells can hold a maximum of
10 electrons. And p subshells can hold a maximum
of six electrons.
Let’s begin writing the electronic
configuration for a titanium atom. Beginning with hydrogen, we move
across period one and write 1s2. Moving on to period two, we fill
the 2s subshell with two electrons and write 2s2. It’s important to remember to fill
each subshell with the maximum number of electrons it can hold until we reach the
final subshell. Next, continuing to move across
period two, we can fill the 2p subshell with six electrons and write 2p6. Now, moving across period three to
fill both the 3s and 3p subshells, we can write 3s2 3p6.
Finally, we have reached period
four, which represents the valence electron shell of the titanium atom. First, we will fill the 4s subshell
with two electrons and write 4s2. Next, we move into the 3d subshell
and count over to where titanium is located. Because titanium is the second
element in the 3d subshell block, we write 3d2.
It’s important to remember that the
coefficient used for d subshells is one less than that used for s and p subshells in
the same period. The electronic configuration can be
written with the subshells in order of increasing energy or increasing 𝑛-value.
Let’s move forward with the
subshells written in order of increasing 𝑛-value. The first five subshells represent
the core electrons of the titanium atom, and the 3d and 4s subshells represent the
valence electrons. We can condense the electronic
configuration of the core electrons by writing the symbol of the noble gas it
represents. This part of the electronic
configuration is represented by argon, which we write inside brackets. Then we finish up by writing the
subshells that contain the valence electrons.
Now that we’ve written the
condensed notation for a titanium atom, let’s write it for the titanium two plus
ion. When a titanium atom forms the
titanium two plus ion, it loses two electrons. When we write electronic
configurations for period four transition metal ions, we remove electrons from the
4s subshell first and the 3d subshell second. Therefore, we need to remove the
two electrons from the 4s subshell. When we write the electronic
configuration for the ion, we no longer need to write the 4s subshell. Therefore, the electronic
configuration of the titanium two plus ion is brackets Ar 3d2, or answer choice
(D).
