Page 33 - Curriculum Visions Dynamic Book

Th see Thorium Thallium (Tl)
Element 81. A blue–grey, malleable, lead-like metal that is part of group 3 (the boron group) in the Periodic Table. It rapidly oxidises in air and develops a thick oxide coating. It is soft enough to be cut with a knife. Thallium salts burn with a bright green flame.
Discovery
It was discovered in England in 1861 by Sir William Crookes. It is the 60th most abundant element on the Earth’s surface.
Technology
Thallium sulphate is colourless, odourless, and tasteless. It was once used to kill rodents and insects.
Thallium sulphide changes its electrical properties when exposed to light and so is part of photocells. It can help to produce glasses with a low melting point.Thallium bromide-iodide crystals can detect infra- red radiation. It was once combined wit mercury in thermometers.
The bright green colour produced during burning made it a colouring material in fireworks.
Geology
Thallium does not occur as a native element and its minerals are rare. Thallium comes from a by-product of refining zinc, lead and iron. It is most commonly recovered from the dust that rises in the chimney during the smelting of iron pyrites.
Biology
Thallium is not found in living things, but it can be absorbed by the skin, and
it then builds up in the body, affecting the nervous system. It was once used as a medicine for treating ringworm and skin infections. Because it can be extremely toxic to people, many applications of the element have been stopped.
Key facts...
Name: thallium
Symbol: Tl
Atomic number: 81
Atomic weight: 204.38
Position in Periodic Table: group 3 (13) (boron
group); period 6
State at room temperature: solid
Colour: blue–grey
Density of solid: 11.85 g/cc
Melting point: 303.5°C
Boiling point: 1,457°C
Origin of name: from the Greek word thallos,
meaning green shoot because it shows a
green line when examined in a spectrometer Shell pattern of electrons: 2–8–18–32–18–3
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