Calcium is a rather soft (though harder than lead), gray, metallic element
that can be extracted by electrolysis from fused calcium chloride. It
burns with a yellow-red flame and forms a white nitride coating when exposed
to air. It reacts with water, displacing a hydrogen atom from the structure,
then forming calcium hydroxide.
Chromium is a member of the transition metals, in group 6. Chromium(0) has
an electronic configuration of 4s13d5, due to the lower energy of the high
spin configuration. Chromium exhibits a wide range of possible oxidation
states. The most common oxidation states of chromium are +2, +3, and +6,
with +3 being the most stable. +1, +4 and +5 are rare. Chromium compounds of
oxidation state +6 are powerful oxidants.
Copper has played a significant part in the history of mankind, which has
used the easily accessible uncompounded metal for nearly 10,000 years.
Civilizations in places like Iraq, China, Egypt, Greece and the Sumerian
cities all have early evidence of using copper. During the Roman Empire,
copper was principally mined on Cyprus, hence the origin of the name of the
metal as Cyprium, "metal of Cyprus", later shortened to Cuprum.