Francium

The mineral thorite, which may contain a few atoms of francium at any time.

Francium is a radioactive alkali metal and is the 87th element in the periodic table. It's in period 7 and is the heaviest alkali metal discovered. Francium is found in uranium ores at a concentration about 18 orders of magnitude lower than the concentration of uranium, which makes it impossible to obtain it in any form except as a tracer. Its isotopes ²⁰⁹Fr, ²¹⁰Fr, and ²¹¹Fr can be synthesized by reacting ¹⁹⁷Au with ¹⁸O, and the resulting ions purified electromagnetically. This allows capture of small numbers of ions (only 300,000 atoms of it produced as the largest sample). Such samples are self-luminous, allowing them to be photographed. Francium may be the rarest element to have been photographed in pure form.

Nuclear properties

Francium has been predicted to have almost 100 isotopes, ranging from the neutron dripline near ²⁹⁰Fr down to ¹⁹⁰Fr. Of these, 34 isotopes ranging from ²³²Fr to ¹⁹⁹Fr have been observed (plus 11 isomers).

Isotopes from the dripline down to ²²⁴Fr are both observed and predicted to decay solely by beta emission. Fission is not expected to play a role even in the heaviest isotopes. A minor (BR = 0.00006) alpha decay branch appears at ²²³Fr, disappears at ²²²Fr, becomes dominant at ²²¹Fr, and becomes the only significant mode of decay between ²¹⁹Fr and ²¹⁴Fr. At ²¹³Fr, whose neutron count is 126, positron emission (positive beta) appears as a decay mode which lasts down to ²⁰¹Fr and is the dominant branch in two isotopes. Below that, alpha decay is the only mode observed or predicted down to ¹⁹²Fr, The two lightest isotopes, ¹⁹¹Fr and ¹⁹⁰Fr are predicted to decay by proton emission. Half-lives of Fr isotopes are predicted and observed to rise as A falls, reaching 1 sec around ²³⁶Fr, 2.47 min at ²²⁷Fr, and peaking at 22.0 min (1320 +/- 4.2 sec) in ²²³Fr. Half lives rise along with A from the lightest isotopes, reaching 1 sec at ²⁰⁴Fr (and its isomers), 1 min at ²¹⁰Fr, and peaking at 20.0 min (1200 +/- 3.6 sec) in ²¹²Fr. Between ²²³Fr and ²¹²Fr, half-lives fall off; dropping below 1 min at ²²⁰Fr, 1 sec at ²¹⁹Fr, 1 ms at ²¹⁷Fr, and 1 microsec at ²¹⁶Fr to reach a minimum of 86 ns (8.6E-08 sec) in ²¹⁵At. ²¹⁴At, recovers to millisecond stability and ²¹³At has a half-life of 35 sec. This dip and recovery is a result of instability at neutron counts slightly greater than 126.

Francium is synthesized in supernovae and neutron star mergers at roughly the same rate as Th or U. Beta-decay cascades from near the dripline reach Z = 87 at ²²¹Fr, ²²³Fr, and all isotopes heavier than ²²³Fr. All other isotopes are blocked at lower Z. This initial surge in abundance will disappear completely within 2 days, leaving only ²²³Fr in equilibrium with its chain head ²³⁵U. ²²¹Fr is sometimes described as remaining in trace amounts, but the chain head of that isotope, ²³⁷Np, is itself the product of neutron irradiation generated by the rare spontaneous fission branch of ²³⁸U. The quantity of ²²¹Fr in existence not significant.

Atomic properties

Francium is an alkali metal. An alert reader commented that it is the second most active metal, after Cs, its 6^th Period homolog. Since light isotopes of Fr are easy to make, the element's chemical properties have been studied in detail. Measuring its bulk properties, such as density, may be within the power of some laboratories; but they're not on this planet. We've seen the only real appearance of bulk Fr - glowing plasma. Atoms of ²²³Fr are so rare in minerals that the strains their presence as 1+ ions, instead of 2+ or 3+, is negligible. The element's chemistry is of academic importance, but does not factor into where it fits into nature.

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

02-19-22