Electron Distribution Mnemonics

 Electrons tend to arrange themselves around nuclei  so that they have the lowest possible energy. They would all like to get into the lowest energy level, sometimes called the K-shell, but are prevented from doing so by some rules that pop up in quantum mechanics. 




A mnemonic for the entire periodic table of the elements recalls the names and abbreviations of all the elements, their basic electron structures, and some properties. Elements are presented in chemically useful groupings with a method that allows one to position an element without recreating the entire table. With two additional lines one can derive all the major elements and the trace elements required by humans. Another verse identifies anomalies in orbital filling. 


An energy level  is a quantum mechanical system or particle that is bound, confined spatially, can only take on certain discrete values of energy, as opposed toclassical particles, which can have any energy. These values are called energy levels. The term is most commonly used for the energy levels of electrons in atoms or molecules, which are bound by the electric field of the nucleus. The energy spectrum of a system with energy levels is said to be quantized.

If the potential energy is set to zero at infinity, the usual convention, then bound electron states have negative potential energy.

Energy levels are said to be degenerate, if the same energy level is shared by more than one quantum mechanical state. They are then called degenerate energy levels.

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. Atomic orbitals are the possible quantum states of an individual electron in the collection of electrons around a single atom, as described by the orbital function. Atomic orbitals exactly describe the shape of this atmosphere only when a single electron is present in an atom. When more electrons are added to a single atom, the additional electrons tend to more evenly fill in a volume of space around the nucleus so that the resulting collection (sometimes termed the atom’s “electron cloud”) tends toward a generally spherical zone of probability describing where the atom’s electrons will be found.

Each orbital is defined by a different set of quantum numbers and contains a maximum of two electrons. The simple names s orbital, p orbital, d orbital and f orbital refer to orbitals with angular momentum quantum number l = 0, 1, 2 and 3 

Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals. For example, the first (K) shell has one subshell, called "1s"; the second (L) shell has two subshells, called "2s" and "2p"; the third shell has "3s", "3p", and "3d"; and so on.^[1]The various possible subshells are shown in the following table:

Subshell label	ℓ	Max electrons	Shells containing it	Historical name
s	0	2	Every shell	sharp
p	1	6	2nd shell and higher	principal
d	2	10	3rd shell and higher	diffuse
f	3	14	4th shell and higher	fundamental
g	4	18	5th shell and higher

• The first column is the "subshell label", a lowercase-letter label for the type of subshell. For example, the "4s subshell" is a subshell of the fourth (N) shell, with the type ("s") described in the first row.
• The second column is the azimuthal quantum number of the subshell. The precise definition involves quantum mechanics, but it is a number that characterizes the subshell.
• The third column is the maximum number of electrons that can be put into a subshell of that type. For example, the top row says that each s-type subshell ("1s", "2s", etc.) can have at most two electrons in it. In each case the figure is 4 greater than the one above it.
• The fourth column says which shells have a subshell of that type. For example, looking at the top two rows, every shell has an s subshell, while only the second shell and higher have a p subshell (i.e., there is no "1p" subshell).
• The final column gives the historical origin of the labels s, p, d, and f. They come from early studies of atomic spectral lines. The other labels, namely g, h and i, are an alphabetic continuation following the last historically originated label of f.

EXERCISES!!!

Electron Configuration Practice Worksheet

In the space below, write the unabbreviated electron configurations of the following elements:

1)  sodium  ____________________________________

2) iron  ___________________________________

3) bromine  ___________________________________

4) barium  _____________________________________

5) neptunium   _____________________________________

Determine what elements are denoted by the following electron configurations:

6)        1s²2s²2p⁶3s²3p⁴  ____________________

7)        1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹  ____________________

 8)      [Kr] 5s²4d¹⁰5p³  ____________________

 9)      [Xe] 6s²4f¹⁴5d⁶  ____________________

 10)     [Rn]  7s²5f¹¹  ____________________

Determine which of the following electron configurations are not valid:

11)         1s²2s²2p⁶3s²3p⁶4s²4d¹⁰4p⁵ ____________________

12)         1s²2s²2p⁶3s³3d⁵  ____________________

13)         [Ra] 7s²5f⁸  ____________________

14)         [Kr]  5s²4d¹⁰5p⁵ ____________________

15)         [Xe]  ____________________

Electron Configurations - Solutions

Note:  The electron configurations in this worksheet assume that lanthanum (La) is the first element in the 4f block and that actinium (Ac) is the first element in the 5f block.  If your periodic table doesn’t agree with this, your answers for elements near the f-orbitals may be slightly different.

1.    sodium            1s²2s²2p⁶3s¹

2.    iron                   1s²2s²2p⁶3s²3p⁶4s²3d⁶

3.    bromine           1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵

4.    barium             1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²

^5.        neptunium      1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f⁵

6.    1s²2s²2p⁶3s²3p⁴  sulfur

7.    1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹  rubidium

8.    [Kr] 5s²4d¹⁰5p³  antimony

9.    [Xe] 6s²4f¹⁴5d⁶  osmium

10. [Rn]  7s²5f¹¹  einsteinium

11. 1s²2s²2p⁶3s²3p⁶4s²4d¹⁰4p⁵ not valid (take a look at “4d”)

12. 1s²2s²2p⁶3s³3d⁵  not valid (3p comes after 3s)

13. [Ra] 7s²5f⁸  not valid (radium isn’t a noble gas)

14. [Kr]  5s²4d¹⁰5p⁵ valid

15. [Xe]  not valid (an element can’t be its own electron configuration)

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