1. The term valence refers to the outermost shell.
QUESTION:
Which of the following has a valence configuration of ns1? A. Na, B. Be, C. Mg, D. Ca
Na 1s2 2s2 2p6 3s or [Ne] 3s1
Be 1s2 2s or [He] 2s2
Mg 1s2 2s2 2p6 3s or [Ne] 3s2
Ca 1s2 2s2 2p6 3s2 3p6 4s2 or [Ar] 4s2
SCRIPT:
Which of the following has a valence configuration of ns1?
PAUSE
CLICK
To answer this question, let’s write the ground state electron configuration for the atoms given.
The term valence refers to the outermost shell.
So the valence shell of sodium is the third shell. N equals three for the outermost shell,… the atom has one electron in the 3s subshell.
HIGHLIGHT 3s1
Therefore, the correct answer is sodium.
All the other atoms…. Beryllium, magnesium, and calcium….have two electrons in their valence shell
HIGHLIGHT 2s2, 3s2, and 4s2
We say that the valence configurations of these atoms are the same… ns2
HIGHLIGHT ns2
This is generally true for atoms belonging to the same column in the periodic table.
Referring to the periodic table, we find Be, Mg and Ca in column 2.
Be, Mg, Ca, and the other elements in group two A all have two electrons in their valence s subshell.
Similarly Na and the other element sin group one A all have one electron in their valence s subshell.
CLICK Because of these, elements belonging to group one A and group two A are sometimes referred to as the s block elements.
END RECORDING
NOTE: valence configuration of Be, Mg, and Ca is ns2

2. s block
nsx

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