Radiometric methods gave better results. After the radioactive decay series of ²³⁵U, ²³⁸U and ²³²Th with stable lead as end-products had been studied, it was assumed that radioisotopes of element 87 exist as intermediate members of these decay series. As early as 1914, Meyer, Hess and Paneth studied a carefully purified ²²⁷Ac preparation and observed a-particles with a range of 3.5cm, which they attributed to element 87. 

In 1939, Mme. Marguerite Perey, of the Curie Institute in Paris, thoroughly studied a-particles of the same range in the decay of a radioactive ²²⁷Ac sample, and found a daughter b^--active decay product with T_1/2=21 min. The chemical properties of this product were close to those of caesium. Thus, for example, the b^--activity remained completely in the filtrate after precipitation of BaCO₃, lead and bismuth sulphides and lanthanum hydroxide and fluorides, but passed quantitively into a caesium prechlorate precipitate. It was thus established that this is an isotope of element 87 with mass 223. This isotope was originally designated as "Actinium-K" (Ac-K), along with other decay products of actinium.

In 1946, Mlle. Perey termed this element francium (in honour of her native France) and in 1949, the IUC (International Union of Chemists) adopted this name and assigned the symbol Fr to the new element. 

Of the first 101 chemical elements, francium is the most unstable. The closest to it is astatine (At), which has a maximum T_1/2 = 8½ hours.
 

The appearance of the comparatively long-lived ²¹²Fr amongst the shorter-lived francium isotopes is not accidental, but is a logical consequence of the regular properties of the a-active isotopes of heavier elements according to which the value of Ea in the isotopes of one element increases linearly with decrease in mass number A. This dependence departs from linearity only near nuclei that have a filled shell of 126 neutrons; q.v. Fig 1. 

The existence of a francium isotope with a neutron number of 125 (equating to ²¹²Fr) was assumed, with Ea minimal compared to the neighboring isotopes. This isotope was found in the products of thorium irradiated by 350MeV protons. ²¹²Fr with Ea approx. = 6.4 MeV and T_1/2 = 19.3 minutes was found in 1950. The main source for the preparation of this isotope is products of the fission of Th and U by high energy protons.

The cross-sections of formation of the francium isotopes £ 220 during the fissioning of uranium nuclei by 660 MeV protons have been calculated (Fig 2), and ²²⁰Fr should have the maximum yield (just under 10 mbarns). The cross-section of ²¹²Fr is comparatively low, at 0.2 mbarns. When thorium nuclei are fissioned, the cross-section of formation of ²¹²Fr should be higher. A higher yield of ²¹²Fr is attained in the reaction ¹⁹⁷Au(²²Ne;a,3n)Fr²¹². The decay scheme of ²¹²Fr is shown in Fig 3.

In accordance with the pattern of a-decay the isotopes with a neutron number (N) of 128 have the shortest half-life and the highest Ea. ²¹⁵Fr is such an isotope (Fig 1). The two juxtaposed isotopes ²¹⁴Fr and ²¹⁶Fr are also short-lived compared to isotopes with A £ 213 and A ³ 217. For isotopes with A between 215 and 221, function Ea is linear, Fig 1; hence, the half-lives also increase. The isotope ²²²Fr is the lightest b^--activity francium isotope. 

An almost complete list of known isotopes (there are allegedly 34 as at 2000) with their associated atomic weights and half-lives is shown in Fig 4.  N (the number of neutrons) may be obtained by subtracting 87 from the isotope number, #.  

In this table:
ec denotes electron capture (where an electron is caught, the upshot of which is that a proton changes into a neutron, thus changing the atom into an element with Z equal to one less, ie, Radon (86) in Francium's (87) case). The value of A remains constant, as the net effect of losing a proton and gaining a neutron is zero.
a denotes alpha decay; here, a helium nucleus (2 protons, 2 neutrons) is ejected from the francium nucleus, leaving an atom with Z equal to two less, ie, Astatine (85).  This is because the number of protons dictates what element an atom is.  The value of A decreases by four (2 protons + 2 neutrons).
b denotes beta decay; here, a neutron decays into an electron and proton.  The upshot here is that Z increases by one (Radium (88)) as there is now one more proton in the nucleus and the electron is ejected, and it is this electron that is detected as the beta radiation. The value of A remains constant, as the net effect of losing a neutron and gaining a proton is zero.

Note that different sources state different numbers of isotopes; I shall try and list as many as I can glean from those sources.  In any case, the only 'natural' isotope of Francium found in nature is ²²³Fr which is part of the actinium decay series.  ²²¹Fr is part of the neptunium decay series, but this tends not to be 'natural'. 
 

# A T1/2 Decay process 201 201 0.048 s a®197At 202 202 0.34 s a®198At 203 203 0.55 s a®199At 204 204 2.1 s a®200At 205 205 3.9 s a®201At 206 206 16 s a®202At 207 207 14.8 s a®203At 208 208 59 s a®204At; ec®208Rn 209 209 50 s a®205At; ec®209Rn 210 209.9964 3 m 12 s a®206At; ec®210Rn 211 210.99553 3 m 6 s a®207At; ec®211Rn 212 211.99618 20 m a®208At; ec®212Rn 213 212.99617 34.6 s a®209At; ec®213Rn 214 213.99895 5.1 x 10-3 s a®210At 215 215.00033 1.2 x 10-7 s a®211At

# A T1/2 Decay process 216 216.00319 7 x 10-7s a®212At; ec®216Rn 217 217.00462 2.2 x 10-5 s a®213At 218 218.00756 7 x 10-7 s a®214At 219 219.00924 21 s a®215At 220 220.01231 27.4 s a®216At 221 221.01425 4 m 54 s a®217At 222 222.01754 14 m 24 s a®218At 223 223.01973 21 m 48s a®219At;b+®223Ra 224 224.02323 2 m 42s b-®224Ra 225 225.02561 3 m 54 s b-®225Ra 226 226.0293 48 s b-®226Ra 227 227.0318 2 m 24s b-®227Ra 228 228 39 s b-®228Ra 229 229 50 s b-®229Ra

All the isotopes with masses ³ 215 were obtained by fissioning U or Th nuclei with fast particles. The cross-sections of formation of these isotopes are between 1 and 7 mbarns when U is fissioned with 660 MeV protons.

The isotope ²²³Fr has been the most exhaustively studied. Its decay scheme is shown in fig 5. Possible a-decay of ²²³Fr with an energy of 5.5 ± 0.2 MeV was predicted from the empirical laws for a-active isotopes; the probability is between 6 x 10^-4 and 4 x 10^-5 of the b^--decay. By means of high-speed photographic plates, a-particles with an energy of 5.38 ± 0.08 MeV were observed in the decay of ²²³Fr. The ratio a/b was 6 x 10^-5. 

²²⁷Ac is the main source of ²²³Fr, formed as the result of the a-decay of ²²⁷Ac; the a-decay is 1.2% of the b^--decay. The ²²⁷Ac preparations are obtained either by the waste products of the uranium industry or by irradiating ²²⁶Ra in a nuclear reactor by the reaction: 

Note that the reported number (and details) of francium isotopes varies greatly with source, hence the caveat on the number of actual isotopes that exist or have been created.
 

 

²²⁷Ac ¾® 0.2 mg
²²³Fr ¾® 3.8 x 10^-10g (0.17 mCurie or 4.65 x 10⁶ dpm)

²²¹Fr ¾® 1.0 x 10^-17g / tonne of natural uranium

In the earth's crust as a whole, at any given time there is probably only 25 - 30g of francium. This amount is, of course, distributed throughout the crust and represents the amount in equilibrium with its host ore. As can be seen from the above figures, the amount in any one place is miniscule. As such, it competes only with astatine for the accolade of being the rarest of the 92 naturally-occurring elements.

No weighable amounts of francium have ever been produced, nor are ever likely to be, due to its extreme transient nature. Radiometric studies of francium have been undertaken with samples of the order 10^-9 g in weight.
 

²²³Fr has been used in limited biological research. In the study of the distribution of Fr, Rb and Cs in different organs of rats, it was found that the alkali metals accumulate chiefly in the kidneys, liver and salivary glands. It was shown that Fr is also fixed in an experimentally-induced sarcoma. Increase in the activity of Fr in the affected tissue appears immediately after onset of growth. This diagnostic method for cancerous diseases could be promising as there is no [little?] damage to the organism because of the short lifetime of either ²²³Fr or ²¹²Fr.

Apart from these applications, there is no commercial application of francium, due to its transient nature.
 

Boiling point -> 677ºC (950 K)

Francium, in the same way as other alkali metals, has no tendency to form complexes or colloids. The adsorptional properties of Fr⁺ have not been studied because of the short life of its isotopes. 

In analogy to Cs⁺, whose adsorption on glass, Teflon and polyethylene has been studied in detail, it can be assumed that the adsorption of Fr⁺ on these surfaces from aqueous solutions at pH 4 thru 11 will be insignificant. It has also been proved that the adsorption of ¹³⁷Cs on a polypropylene surface is considerably less than on glass or Pyrex. It would appear that francium has similar properties.

In contrast to many artificial elements (Pu, Np, Tc, Pm et al), francium cannot ever be obtained in weighable amounts due to there being no long-lived isotopes thereof. Hence, all the chemical and physical properties of francium have been studied with extremely low amounts, typically £ 10^-15g. Given its position in the Periodic Table, francium is expected to be the most electropositive element, carrying on the procession down the Group 1 line from Li to Cs. Francium exists in just one oxidation state, +1. Data on analysis of francium suggest that it is a complete analogue of Rb and Cs; in other words, many of its properties can be inferred from properties of those two elements. As time goes on, these properties are duly verified. The chloride, nitrate, sulfate, fluoride, sulfide, hydroxide, carbonate, acetate and oxalate of francium would be readily soluble in water, but the perchlorate, picrate, iodate, and some salts (such as Fr₉Bi₂I₉) would be sparingly soluble.

According to its position, francium should have a more negative standard potential than caesium (where E₀ = -3.04 V). Therefore, francium can be separated on mercury only. However, very dilute amalgams are unstable; amalgams formed from 10^-9 M 137Cs show this. Attempts to obtain similar results for 10^-14 M francium were unsuccessful even when ultra-pure reagents were used. The francium amalgam decomposes a few minutes after the current is turned off. The amount of francium that passes into mercury at a given potential is less than that of caesium; this proves that francium is separated at a more negative potential than caesium.
 

The problem of separating francium from other alkali elements frequently arises in the analysis of products of different nuclear reactions. In the analysis of natural objects ²²⁷Ac is separated from the main components and then from its decay products. ²²³Fr is separated from ²²⁷Ac after radioactive equilibrium has been established, typically about 2 hours.

There are several documented ways to extract francium; these include extraction, sublimation and ion exchange. These processes are far too detailed to go into here, but the book in the biblography details them. However, a lab at Stony Brook has perfected a technique to capture 10,000 francium atoms at once. For more information, check out their link.
 

"Analytical Chemistry of Technetium, Promethium, Astatine and Francium".

by A.K.Lavrukhina and A.A.Pozdnyakon, Ann Arbor-Humphrey Science Publishers Inc., 1970. Other information gleaned from reference works and own research.
 

• Web Elements is an excellent Periodic Table resource on the web, and has been recently updated.
• The Stony Brook reference details an experiment whereby 10,000 Francium atoms are trapped with the use of lasers. 

This page is now complete! I would only need to add extra information as it comes along, such as more isotopes. Keep checking back for the latest update. Also coming soon will be the other pages in this series - astatine, technetium and promethium. 
This page last updated 20 Dec 2004.