<Tr> <Td> Atomic radius </Td> <Td> 135 pm </Td> <Td> 155 pm </Td> <Td> 150 pm </Td> <Td>? 147 pm </Td> </Tr> <P> Zinc is somewhat less dense than iron and has a hexagonal crystal structure . The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 ° C. Above 210 ° C, the metal becomes brittle again and can be pulverized by beating . Zinc is a fair conductor of electricity . For a metal, zinc has relatively low melting (419.5 ° C, 787.1 F) and boiling points (907 ° C). Cadmium is similar in many respects to zinc but forms complex compounds . Unlike other metals, cadmium is resistant to corrosion and as a result it is used as a protective layer when deposited on other metals . As a bulk metal, cadmium is insoluble in water and is not flammable; however, in its powdered form it may burn and release toxic fumes . Mercury has an exceptionally low melting temperature for a d - block metal . A complete explanation of this fact requires a deep excursion into quantum physics, but it can be summarized as follows: mercury has a unique electronic configuration where electrons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d and 6s subshells . As such configuration strongly resists removal of an electron, mercury behaves similarly to noble gas elements, which form weak bonds and thus easily melting solids . The stability of the 6s shell is due to the presence of a filled 4f shell . An f shell poorly screens the nuclear charge that increases the attractive Coulomb interaction of the 6s shell and the nucleus (see lanthanide contraction). The absence of a filled inner f shell is the reason for the somewhat higher melting temperature of cadmium and zinc, although both these metals still melt easily and, in addition, have unusually low boiling points . Gold has atoms with one less 6s electron than mercury . Those electrons are more easily removed and are shared between the gold atoms forming relatively strong metallic bonds . </P> <P> Zinc, cadmium and mercury form a large range of alloys . Among the zinc containing ones, brass is an alloy of zinc and copper . Other metals long known to form binary alloys with zinc are aluminium, antimony, bismuth, gold, iron, lead, mercury, silver, tin, magnesium, cobalt, nickel, tellurium and sodium . While neither zinc nor zirconium are ferromagnetic, their alloy ZrZn 2 exhibits ferromagnetism below 35 K. Cadmium is used in many kinds of solder and bearing alloys, due to a low coefficient of friction and fatigue resistance . It is also found in some of the lowest - melting alloys, such as Wood's metal . Because it is a liquid, mercury dissolves other metals and the alloys that are formed are called amalgams . For example, such amalgams are known with gold, zinc, sodium, and many other metals . Because iron is an exception, iron flasks have been traditionally used to trade mercury . Other metals that do not form amalgams with mercury include tantalum, tungsten and platinum . Sodium amalgam is a common reducing agent in organic synthesis, and is also used in high - pressure sodium lamps . Mercury readily combines with aluminium to form a mercury - aluminium amalgam when the two pure metals come into contact . Since the amalgam reacts with air to give aluminium oxide, small amounts of mercury corrode aluminium . For this reason, mercury is not allowed aboard an aircraft under most circumstances because of the risk of it forming an amalgam with exposed aluminium parts in the aircraft . </P> <P> Most of the chemistry has been observed only for the first three members of the group 12 . The chemistry of copernicium is not well established and therefore the rest of the section deals only with zinc, cadmium and mercury . </P>

What do sodium and magnesium have in common