Boron
Boron (5B) is a Group 13 element. Boron has properties which are borderline between metals and non-metals. It is a semiconductor rather than a metallic conductor. Chemically it is closer to silicon than to aluminium, gallium, indium, and thallium. Crystalline boron is inert chemically and is resistant to attack by boiling HF or HCl. When finely divided it is attacked slowly by hot concentrated nitric acid.
Aluminium
Pure aluminium (13Al) is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), nonmagnetic and nonsparking. It is somewhat decorative. It is easily formed, machined, and cast. Pure aluminium is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminium is an abundant element in the earth's crust, but it is not found free in nature. The Bayer process is used to refine aluminium from bauxite, an aluminium ore.
Gallium
Gallium (31Ga) is the only metal, except for mercury, caesium, and rubidium, which can be liquid near room temperatures; this makes possible its use in high-temperature thermometers. It has one of the longest liquid ranges of any metal and has a low vapour pressure even at high temperatures. Ultra-pure gallium has a beautiful, silvery appearance, and the solid metal exhibits a conchoidal fracture similar to glass. The metal expands on solidifying; therefore, it should not be stored in glass or metal containers, as they may break as the metal solidifies. High-purity gallium is attacked only slowly by mineral acids. Gallium arsenide is capable of converting electricity directly into coherent light and gallium arsenide is a key component of LEDs (light emitting diodes).
Indium
Indium (49In) is a very soft, silvery-white metal with a brilliant lustre. The pure metal gives a high-pitched "scream" when bent. It wets glass, as does gallium. It is useful for making low-melting alloys. An alloy of 24% indium and 76% gallium is liquid at room temperature. Canada produces the majority of of the world's supply of indium.
Thallium
When freshly exposed to air, thallium (81Tl) exhibits a metallic lustre, but soon develops a bluish-grey tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in air, and in the presence of water the hydroxide is formed. The metal is very soft and malleable. It can be cut with a knife. The element and its compounds are toxic and should be handled carefully. Thallium may cause cancer.
