Lanthanum

Lanthanum (La) is the name of element 57. It is the first member of a series of 14 elements whose chemical behavior is characterized by the number of electrons in their 4f shells (plus the occasional appearance of a 5d electron). Interestingly enough, La itself has no 4f electrons. It is among the exceptions which have a 5d electron. In compounds, it usually takes the +3 oxidation state, as in La₂O₃.

Lanthanum has odd Z, so it would be expected to have only one or two stable isotopes. It has one, ¹³⁹La. When only one isotope of an element is stable, an isotope two neutrons heavier or lighter often has a long half-life - or even a very long half-life such as that of ¹⁸⁷Re. In lanthanum, ¹³⁷La has a half-life of 6E04 yrs. But the isotope between them, ¹³⁸La falls just short of being effectively stable. That's not a common occurrence, but the pattern does appear elsewhere, such as ⁴⁰K. In the case of 138La, beta decay releases a lot of energy - which implies a short half-life - but beta decay to ¹³⁸Ce is inhibited by the difference in spin between the two. Normal beta decay mechanisms are blocked, so decay can take place only by mechanisms which are unlikely to occur. Since a chance at decay rarely comes, ¹³⁸La has a long half-life.

Like La itself, all the lanthanides favor the +3 oxidation state. All the lanthanides have fairly similar oxidation states. As those data hint, minerals containing La contain all the other lanthanides. The best-known ore of La is monazite, M³⁺(PO₄)^3-, where M is one of the lanthanides, or possibly thorium.

Lanthanum is three times as abundant as lead in the earth's crust.

9-Period Periodic Table of Elements
1	1 H																																																																	2 He
2	3 Li	4 Be																																																																	5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg																																																																	13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca																																																																	21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr																																																																	39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba																																																					57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb	71 Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra																																																					89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No	103 Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt	110 Ds	111 Rg	112 Cn	113 Nh	114 Fl	115 Mc	116 Lv	117 Ts	118 Og
8	119 Uue	120 Ubn																															121 Ubu	122 Ubb	123 Ubt	124 Ubq	125 Ubp	126 Ubh	127 Ubs	128 Ubo	129 Ube	130 Utn	131 Utu	132 Utb	133 Utt	134 Utq	135 Utp	136 Uth	137 Uts	138 Uto	139 Ute	140 Uqn	141 Uqu	142 Uqb	143 Uqt	144 Uqq	145 Uqp	146 Uqh	147 Uqs	148 Uqo	149 Uqe	150 Upn	151 Upu	152 Upb	153 Upt	154 Upq	155 Upp	156 Uph	157 Ups	158 Upo	159 Upe	160 Uhn	161 Uhu	162 Uhb	163 Uht	164 Uhq	165 Uhp	166 Uhh	167 Uhs	168 Uho	169 Uhe	170 Usn	171 Usu	172 Usb
9	173 Ust	174 Usq
Alkali metal Alkaline earth metal Lanthanide Actinide Superactinide Transition metal Post-transition metal Metalloid Other nonmetal Halogen Noble gas predicted predicted predicted predicted predicted predicted predicted predicted predicted

(12-09-21)