Chemical Elements

Alphabetically :

A PG-rated French mnemonic   (about a  weird  family diner)  

K	Ho He!
L	Lili Becta Bien Chez Notre Oncle François Nestor.
M	Napoléon Mangea Allègrement Six Poulets Sans Clamser Après.
N	Karl Carrément Scanda :  "Tirez-Vous, Craignez Mon Féroce Courroux...  Nichée Cupide, Zinzins Gâteux, Gérontes Assurément Séniles, Brigands Kremlinesques."

  Main Classification :

Transition Metals :   The 3^rd to 12^th column  (B columns).

As of January 2005, the first unnamed element for which discovery has been claimed is element 112.  It still goes by the temporary name of Ununbium [IUPAC system].  Alternately, it can be identified as eka-mercury (or eka- hydrargyrum, eka-Hg) the same way element 111 was formerly known as eka-gold.  Mendeleev himself introduced the prefix "eka-" to name any undiscovered element after whatever appears above it in the periodic table (such elements are chemically similar).

Electronic Configurations :

• The principal quantum number (n) determines the  shell.  In the absence of external fields, the  (negative)  energy  of a bound electron depends  only  on that number  (it's inversely proportional to  n² ). 
• The azimuthal quantum number (l) ranges from 0 to n-1 within a given shell and determines what's called a  subshell, normally designated by a traditional letter s (l=0), p (l=1), d (l=2) or f (l=3).

  Electrons per Subshell Subshell Maximum  s   0  2 p 1 6 d 2 10 f 3 14   L 2(2L+1)

  The etymology of these letters can be traced to the spectroscopic vocabulary predating quantum mechanics (s=sharp, p=principal, d=diffuse, f=fundamental).  A subshell is normally denoted by the number of the shell (n) followed by such a letter, yielding a designation like  ns, np, nd or nf  (e.g., "3d"). 
• The magnetic quantum number (m) ranges from -L to L within a given subshell and determines an  orbital, which may "contain" no more than two electrons of opposite  spins  (see next). 
• The spin of an electron is a two-valued quantum number (s = ±½).

The  Pauli Exclusion Principle  states that two electrons cannot be in the same quantum state.  They must differ in at least one of the values of the above 4 quantum numbers.  This implies that a subshell (n,l) may contain no more than 2(2l+1) electrons, as tabulated above  (the total number within the whole shell is at most 2n² ).

1s
2s          2p
3s          3p
4s      3d  4p
5s      4d  5p
6s  4f  5d  6p
7s  5f  6d  7p

The minimal energy of the electronic cloud surrounding a lone nucleus is achieved when electrons occupy available subshell room in the order at left, starting with the 1s subshell.  This simplified version of the  Aufbau principle  explains the structure of the periodic table of elements, where elements with similar chemical properties are listed in the same column:  The chemical properties of an element depend mostly on the  valence  electrons located in the outermost subshell(s) which are usually the least favored energetically  (with the reservations noted below, in the case of "f" subshells).

The electronic configuration around a nucleus may be summarized by listing all nonempty subshells in the above order of increasing energies (1s, 2s, 2p, 3s, etc.) with a superscript indicating the number of electrons in each.  The repartition of electrons into orbitals of the same subshell is usually ignored.

A complementary term symbol is sometimes added to better describe the ground configuration.  It may be obtained using Hund's Rule,  a set of empirical recipes due to Friedrich Hund (1896-1997).  Electrons avoid pairing up on the same orbital unless all the orbitals of the subshell are occupied.

For brevity, the configuration of a noble gas may be denoted by its bracketed symbol  [as a prefix]  in the electronic configuration of subsequent elements.  Note that all subshells of noble gases are full.  Chemical inertness is due to an outter shell containing a total of 8 electrons (except for helium).

In the periodic table, successive "transition metals" correspond to the "filling" of a "d" subshell (from 1 to 10 electrons).  Adding 1 to 14 electrons to the empty "f" subshell of Lanthanum yields the other elements of the Lanthanide series (Z = 58 to 71) whose chemical similarity with Lanthanum may be explained by stating that the "f" subshell corresponds to orbitals that are "closer" to the nucleus than those of the previous "s" subshell, so "f" electrons are less likely fo be valence electrons  (the same situation repeats with Actinium and the Actinides series, from Z = 89 to 103).  This geometrical explanation should not be taken too literally...

For completeness, it should be noted that the energy levels of some subshells are so close that the pairing of electrons may lead to a few exceptions  (in particular for Cr and Cu)  in the application of the simplified  Aufbau principle  presented above.

Geometric Designations of the Orbitals

N	L	M
		-2	-1	0	+1	+2
1	0			1s
2	0			2s
	1		2py	2pz	2px
3	0			3s
	1		3py	3pz	3px
	2	3d xy	3d yz	3d z2	3d xz	3d x2-y2