ergy bands), in insulators it lies in
the valence band, and in semicon-
ductors it falls in the gap between
the conduction band and the valence
band. At absolute zero all the elec-
trons would occupy energy levels up
to the Fermi level and no higher lev-
els would be occupied. It is named
after the Italian-born US physicist En-
rico Fermi (1901–54).
fermion An *elementary particle
(or bound state of an elementary par-
ticle, e.g. an atomic nucleus or an
atom) with half-integral spin; i.e.
a particle that conforms to Fermi–
Dirac statistics (see quantum statis-
tics). Compare boson.
fermium Symbol Fm. A radioactive
metallic transuranic element belong-
ing to the *actinoids; a.n. 100; mass
number of the most stable isotope
257 (half-life 10 days). Ten isotopes
are known. The element wasÜrst
identiÜed by A. Ghiorso and associ-
ates in debris from theÜrst hydro-
gen-bomb explosion in 1952. It is
named after Enrico Fermi.
A
- Information from the WebElements site
ferrateAn iron-containing anion,
FeO 4 2–. It exists only in strong alka-
line solutions, in which it forms pur-
ple solutions.
ferric alum One of the *alums,
K 2 SO 4 .Fe 2 (SO 4 ) 3 .24H 2 O, in which the
aluminium ion Al3+is replaced by
the iron(III) (ferric) ion Fe3+.
ferric chloride testA *presump-
tive test for morphine. The reagent is
a 10% solution of ferric chloride
(iron(III) chloride, Fe Cl 3 ) in water.
With morphine a blue-green col-
oration occurs, changing to green.
ferric compounds Compounds of
iron in its +3 oxidation state; e.g. fer-
ric chloride is iron(III) chloride, FeCl 3.
ferricyanideA compound contain-
ing the complex ion [Fe(CN) 6 ]3–, i.e.
the hexacyanoferrate(III) ion.ferrimagnetismSee magnetism.
ferrite1.A member of a class of
mixed oxides MO.Fe 2 O 3 , where M is a
metal such as cobalt, manganese,
nickel, or zinc. The ferrites are ce-
ramic materials that show either fer-
rimagnetism or ferromagnetism, but
are not electrical conductors. For
this reason they are used in high-
frequency circuits as magnetic cores.
2.See steel.
ferroalloys Alloys of iron with
other elements made by smelting
mixtures of iron ore and the metal
ore; e.g. ferrochromium, ferrovana-
dium, ferromanganese, ferrosilicon,
etc. They are used in making alloy
*steels.
ferrocene An orange-red crys-
talline solid, Fe(C 5 H 5 ) 2 ; m.p. 173°C. It
can be made by adding the ionic
compound Na+C 5 H 5 – (cyclopentadi-
enyl sodium, made from sodium and
cyclopentadiene) to iron(III) chloride.
In ferrocene, the two rings are paral-
lel, with the iron ion sandwiched be-
tween them (hence the name
sandwich compound: see formula).
The bonding is between pi orbitals
on the rings and d-orbitals on the
Fe2+ion. The compound can undergo
electrophilic substitution on the C 5 H 5
rings (they have some aromatic char-
acter). It can also be oxidized to the
blue ion (C 5 H 5 ) 2 Fe+. Ferrocene is the223 ferrocene
f
FeFerrocene