Mendeleev’s law See periodic
law.mendeleviumSymbol Md. A radio-
active metallic transuranic element
belonging to the *actinoids; a.n. 101;
mass number of theÜrst discovered
nuclide 256 (half-life 1.3 hours). Sev-
eral short-lived isotopes have now
been synthesized. The element was
Ürst identiÜed by Albert Ghiorso,
Glenn Seaborg (1912–99), and associ-
ates in 1955.
A- Information from the WebElements site
Mendius reaction A reaction in
which an organic nitrile is reduced
by nascent hydrogen (e.g. from
sodium in ethanol) to a primary
amine:
RCN + 2H 2 →RCH 2 NH 2
mentholA white crystalline ter-
pene alcohol, C 10 H 19 OH; r.d. 0.89;
m.p. 42°C; b.p. 103–104°C. It has a
minty taste and is found in certain
essential oils (e.g. peppermint) and
used as aÛavouring.
mercaptans See thiols.
mercapto group See thiols.
mercuric compounds Com-
pounds of mercury in its +2 oxida-
tion state; e.g. mercuric chloride is
mercury(II) chloride, HgCl 2.mercurous compounds Com-
pounds of mercury in its +1 oxida-
tion state; e.g. mercury(I) chloride is
mercurous chloride, HgCl.
mercury Symbol Hg. A heavy sil-
very liquid metallic element belong-
ing to the *zinc group; a.n. 80; r.a.m.
200.59; r.d. 13.55; m.p. –38.87°C; b.p.
356.58°C. The main ore is the sul-
phide cinnabar (HgS), which can be
decomposed to the elements. Mer-
cury is used in thermometers,
barometers, and other scientiÜc ap-
paratus, and in dental amalgams. Theelement is less reactive than zinc and
cadmium and will not displace hy-
drogen from acids. It is also unusual
in forming mercury(I) compounds
containing the Hg 2 2+ion, as well as
mercury(II) compounds containing
Hg2+ions. It also forms a number of
complexes and organomercury com-
pounds.
A- Information from the WebElements site
mercury cell A primary *voltaic
cell consisting of a zinc anode and a
cathode of mercury(II) oxide (HgO)
mixed with graphite. The electrolyte
is potassium hydroxide (KOH) satu-
rated with zinc oxide, the overall re-
action being:
Zn + HgO →ZnO + Hg
The e.m.f. is 1.35 volts and the cell
will deliver about 0.3 ampere-hour
per cm^3.
mercury(I) chloride A white salt,
Hg 2 Cl 2 ; r.d. 7.15; sublimes at 400°C. It
is made by heating mercury(II) chlo-
ride with mercury and is used in
calomel cells (so called because the
salt was formerly called calomel) and
as a fungicide.
mercury(II) chloride A white salt,
HgCl 2 ; r.d. 5.4; m.p. 276°C; b.p.
302 °C. It is made by reacting mer-
cury with chlorine and used in mak-
ing other mercury compounds.mercury(II) fulminate A grey
crystalline solid, Hg(CNO) 2 .½H 2 O,
made by the action of nitric acid on
mercury and treating the solution
formed with ethanol. It is used as a
detonator for cartridges and can be
handled safely only under cold water.
mercury(II) oxide A yellow or red
oxide of mercury, HgO. The red form
is made by heating mercury in oxy-
gen at 350°C; the yellow form, which
differs from the red in particle size,
is precipitated when sodium hydrox-Mendeleev’s law 348m