Video Transcript
A recently discovered element has a
predicted electron configuration of brackets Rn 5f14 6d10 7s2 7p3. In what group of the periodic table
would this element likely be found?
The electron or electronic
configuration of an atom describes how many electrons the atom has, as well as how
these electrons are arranged into different electron shells and subshells. When writing the electron
configuration, electron subshells use a letter code, s, p, d, or f, to indicate the
type of atomic orbitals they contain.
The periodic table can be divided
into blocks that represent these subshells. Elements found in the same block
have valence electrons in the same type of subshell. For example, elements found in the
p block, which are the elements found in groups 13 through 18, excluding helium,
have one or more valence electrons found in the p subshell. It’s helpful to remember that
excluding the elements found in the d and f blocks, the period that an element is
found in represents the outermost or valence electron shell. The order in which electrons fill
up the various subshells in an atom is based on increasing energy. This rule is known as the Aufbau
principle.
While it’s helpful to know that the
subshell blocks shown in the periodic table here are organized from lowest to
highest energy, the following diagram shows the relative energy values of the
electron subshells. The electron configuration provided
in this problem is given in a shorthand form called condensed notation. In this notation, the chemical
symbol of the noble gas above the period that the element is in is written inside
brackets. The remaining subshells are written
after this. Rn or radon is in the 6p subshell
block. The next lowest energy subshell is
7s, which holds two electrons.
If we look very carefully at the
diagram on the right, we see that the next lowest subshell is 5f. This is a little more difficult to
see on the periodic table because the f blocks of periods six and seven are pulled
out below the table. The next lowest energy subshell is
6d, which holds 10 electrons. And finally, we reach the 7p
subshell.
The two forms of the electron
configuration that we’ve written are both accepted by chemists. The first one puts the subshells in
order by principal quantum number or 𝑛. The second one adheres to the
Aufbau principle and puts the subshells in order of increasing energy. However, in both forms, it’s the
subshell that’s written last that helps us determine the group that the element is
in. All p subshells hold a maximum of
six electrons. This element has three electrons in
its 7p subshell. Therefore, it is the third element
in the 7p subshell block. Now, we can see that this element
is in group 15.
In what group of the periodic table
is the recently discovered element likely to be found? The answer is group 15.
