1. Valence shell = outermost shell. Example:
QUESTION:
Which of the following does not have a valence shell of n=4? A. Ga, B. Al, C. K, D. Mn
Valence shell = outermost shell. Example:
Ga 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1
Valence shell: n=4
Al 1s2 2s2 2p6 3s2 3p1
K s2 2s2 2p6 3s2 3p6 4s1
Mn 1s2 2s2 2p6 3s2 3p6 4s2 3d5
SCRIPT:
Which of the following does not have a valence shell of n=4? Gallium…
Aluminum…
Potassium…
Or Manganese….
PAUSE
CLICK
The term valence shell means outermost shell. This is the shell whose electrons are, on average, farthest from the nucleus.
The larger the quantum number n,… the farther from the nucleus.
For example, the electron configuration of gallium is…
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1
Note that this is the ground state configuration; unless otherwise specified, when we talk
about an atom and their electron configuration, we are referring to its ground state configuration.
The valence shell, or outermost shell is the shell with the largest n.
Therefore, the valence shell of gallium is the fourth shell.
If we were to write the electron configuration of the other atoms, we get the following…
CLICK For aluminum, the configuration is 1s2 2s2 2p6 3s2 3p1
For potassium, the configuration is 1s2 2s2 2p6 3s2 3p6 4s1
And for manganese, the configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d5
We can see that the valence shell of aluminum is the third shell.
HIGHLIGHT 3 in 3s2 and 3p1
The valence shell of potassium is the fourth shell…
HIGHLIGHT 4 in 4s1
And the valence shell of manganese is also the fourth shell…
HIGHLIGHT 4 in 4s2
Therefore, the correct answer is aluminum. It’s valence shell is the third shell; n equals 3. For all the other choices, the valence shell is the fourth shell.
We can actually figure out…. Rather easily…, the answer to this question by simply referring to the periodic table.
We can see that potassium…
Manganese…
And gallium…
All belong to period 4, or row number 4. The periodic table is laid out so that the principal quantum number of the valence atoms in a given row all correspond to the row number.
Note that aluminum belongs to row number 3. For its valence shell, n equals 3.
In general,
For elements in row 1, the valence shell is the first shell.
CLICK For elements in row 2, the valence shell is the second shell.
CLICK For elements in row 3, the valence shell is the third shell
For elements in row 4, the valence shell is the fourth shell
CLICK For elements in row 5, the valence shell is the fifth shell
For elements in row 6, the valence shell is the sixth shell
CLICK For elements in row 7, the valence shell is the seventh shell.
The same is true of the Lanthanides. These elements actually belong to row 7.
For elements in row 8, the valence shell is the eighth shell.
CLICK The same is true of the Actinides. These elements actually belong to row 8.
END RECORDING

2. Valence n=1
Valence n=2
Valence n=3
Valence n=5
Valence n=6
Valence n=7
Valence n=8
Valence n=7
Valence n=8

3. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08