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Mendelevium (Md)
Element 101 on the periodic table. An artificial and radioactive element in the actinide series. It was discovered by Albert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson and Glenn T. Seaborg and named after Dmitri Ivanovitch Mendeleev. It is a transuranium element.
Mendeleev, Dmitri I.
A Russian chemist, Dmitri Ivanovitch Mendeleev (1834-1907) created the periodic table of the elements. He was convinced that the key to ordering the elements lay in their atomic weights (see: Atomic mass).
At the time, there were only
57 known elements. When he arranged them in the sequence
of increasing atomic weights, he noted that the chemical properties of the elements were grouped into already familiar families.
To make his table work, he discovered that he had to leave spaces in it. But the spaces in the table predicted the properties of the as yet unknown elements that should be in them. As new elements were discovered, their properties were found to fit exactly into the empty
spaces. The periodic table of the elements also
showed scientists where to look to discover new elements.
Mercury (Hg)
Element 80 on the periodic table. A silvery liquid metal, also called quicksilver, belonging to the transition metals. It has been known since ancient times.
It is occasionally found as a native liquid metal, but much more commonly as the red mineral cinnabar.
Mercury is the only metal element that is liquid at room temperature. In this form it is
used in thermometers. It has very good electrical conductivity and goes into sealed switches. When electricity passes through mercury vapour, it gives off a bluish glow. The vapour is used in street lighting and in fluorescent lamps. Mercury is also alloyed with many metals.
Mercury vapour is poisonous. It once was used in hat making and its effect on hatters gave rise to the term ‘mad as a hatter’.
(See also: Amalgam.)
Metallic bond Metal, metallic element
An element that is a good conductor of electricity and heat, has a metallic lustre, is malleable and ductile, forms cations and has oxides that are bases.
Metals are formed as cations held together by a ‘sea’ of electrons. A metal may also be an alloy of these elements. Examples of metals are sodium, calcium and gold.
Metallic bond
A type of chemical bond found in solid metals. A metal is made of closely packed cations embedded in a ‘sea’ of electrons that bond the ions together.
Every ion is surrounded by six others to make a hexagonal pattern of packing, and this gives metals their high densities. The strong bonds between the ions and the free electrons allow metals to be good conductors of heat and electricity, and means that they are not brittle.
(See also: Covalent bond and Ionic bond.)
 Mercury – Mercury’s strong surface tension keeps the liquid state as small globules.
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