# Question #9326b

##### 1 Answer

It's not possible until you identify the element and assume that it is a NEUTRAL atom, by which point it doesn't matter what notation you use at all.

**KLMN notation**, or "X-ray notation", is an old way of denoting electron configurations, and is not very informative.

Here is how it corresponds to **electron script configurations**:

#overbrace(1s)^("K shell")color(white)(.)overbrace(2s2p)^("L shell")color(white)(.)overbrace(3s3p3d)^("M shell")color(white)(.)overbrace(4s4p4d4f)^("N shell")cdots#

and so on. Take the following unstated atom as an example:

#overbrace(1s^2)^(K) overbrace(2s^2 2p^6)^(L) overbrace(3s^2 3p^6 3d^0)^(M) overbrace(4s^2)^(N)#

One would write this in X-ray notation as:

#2,8,8,2#

See the problem?

** ...Which electrons are which?** All that can be determined is how many electrons there are. One is then stuck with saying "there are 8 electrons in the M shell"... whatever that means.

To determine where the element is, we know it has

- it must be atomic number
#20# (but we can only know that by assuming a neutral atom!). - it must be calcium as a consequence.
- it must be on
**column**#2# ,**row**#4# , by inspection.

Now consider the following:

#overbrace(1s^2)^(K) overbrace(2s^2 2p^6)^(L) overbrace(3s^2 3p^6 3d^10)^(M) overbrace(4s^2 4p^6 4d^5)^(N) overbrace(5s^2)^(O)#

One would write this, rather confusingly, in X-ray notation as:

#2, 8, 18, 13, 2#

and clearly, there are

If we only know the number of electrons, we must assume a NEUTRAL atom, and only after that we can say

- it must be atomic number
#43# . - it must be technetium as a consequence.
- it must be on
**column**#7# ,**row**#5# by inspection.

In this case, the average student might wonder why technetium has more than

*In general, the "octet rule" only applies to #s# and #p# orbitals on the same energy level. But how would we know that? We don't know of angular momentum quantum numbers in X-ray notation, which allow the construction of the octet rule itself...*