Francium

Francium is element 87 (Fr), located in period 7, group 1 and the s block. At room temperature its reference phase is solid. Its electron configuration is [Rn] 7s1.

Atomic number87

Standard atomic weightNo standard atomic weight

Group1

Period7

Blocks

Electron configuration[Rn] 7s1

Electronic structure

What controls its chemistry

The outer electron configuration ends in s¹. Losing that single valence electron gives a +1 ion with a filled inner-shell configuration, so francium compounds are dominated by the +1 oxidation state.

The same outer-shell pattern is shared by the alkali metals. Down the group the outer electron is farther from the nucleus and generally easier to remove, which helps explain the high reactivity of the family.

Chemical forms

Compounds, ions and materials

The dominant chemical form is francium in the +1 oxidation state. Ionic halides, hydroxides and oxygen-containing salts are common; the free metal is much less common in nature because it reacts readily with water, oxygen and other non-metals.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The melting point is 300 K (26.9 °C). The boiling point is 923K (676.9 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where francium is found and used

In practice, francium is encountered in scientific research.

In practice

Examples of real uses

Scientific research

Francium is produced, isolated or measured mainly to test atomic, nuclear and periodic trends rather than for bulk commercial use.

Periodic position

What its neighbours tell us

Francium is in period 7 and group 1. In the neighbourhood shown here, radium is immediately to its right in the same period; caesium is directly above it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationalkali metal

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 32 · 18 · 8 · 1

Density—

Melting point300 K (26.9 °C)

Boiling point923K (676.9 °C)

Pauling electronegativity0.79

First ionisation energy393kJ/mol

Electron affinity46.89 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of francium is associated with Marguerite Perey. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

Francium has no standard atomic weight. There is no characteristic terrestrial isotopic mixture from which a stable abundance-weighted average can be assigned.

Francium has no stable isotope. Its isotopes are radioactive, and their half-lives and decay modes become important whenever the element is measured, handled or used.

Safety

Handling and exposure

Francium is radioactive. Work with it requires radiological controls appropriate to the isotope, activity, radiation type and chemical form.