Post-Transition Metals are a category of chemical elements in the Periodic Table, which are located between the Metalloids and the Transition Metals. They are metallic elements, which possess physical and chemical properties and characteristics close to the margin of the metal-nonmetal borderline. These elements are also known as B-subgroup metals or P-block metals. The following six Periodic Table elements fall under the category of Post-Transition Metals: Gallium (Ga), Indium (In) and Thallium (Tl), which are group 13 elements, Tin (Sn) and Lead (Pb), which are group 14 elements, and Bismuth (Bi), which is an element from group 15.
Physical Characteristics of the Post-Transition Metals
All Post-Transition Metals are metallic elements, which means that they all have metallic properties to a certain degree. While they have a shiny metallic surface, they are quite brittle and soft. These elements are considered as weak metals and they have a poor mechanical strength. Their standard boiling points and melting points are significantly lower than the ones of Transition Metals. Post-Transition Metals have crystalline structures, which form directional or covalent bonds. Post-Transition Metal elements show greater complexity in their bonding than many other metallic elements.
Chemical Properties of the Post-Transition Metals
The covalent bonds are common for Post-Transition Metals, but their tendencies may vary. Instead of forming hydroxides like many other metals do, Post-Transition Metal elements form amphoteric oxides with an acid base. Their electrochemical behavior is notorious and they can also form Zintl phases. Some of them are relatively reactive.
Bonding and reaction to other elements and compounds
The Post-Transition Metals’ ability to form covalent bonds goes hand in hand with their ability to form half-metallic compounds in Zintl phases. Some Post-Transition Metal elements can even form anionic species – Gallium forms ionic gallates, Indium forms ionic indates, Thallium forms ionic thallates, Lead forms ionic plumbates, and Bismuth forms ionic bismuthates. Most of these elements have a +2 oxidation state. Thallium is the only Post-Transition Metal from its group, which has the ability to react to room temperature air, which results in the forming of an amphoteric oxide. Lead can also oxidize, but only in moist air conditions.
Uses and applications of the Post-Transition Metals
Since they have a crystalline structure and are quite soft and brittle, most Post-Transition Metal elements in the Periodic Table don’t have a universal structural use. However, they find applications in metallurgy, in electronics, medicine, pharmaceuticals, nuclear engineering, infrared electronics, glass manufacturing, and gardening.
Tin is used in the manufacturing of steel and of various biocides like herbicides, wood preservatives and fungicides. Lead was once used in the manufacturing of bullets, and bricks made from Lead are used in nuclear engineering as radiation shields. Gallium finds application in electronics – lasers, microwaves, LEDs, as well as in radiopharmaceuticals. Indium is used in electronics as a valuable semiconductor factor, as well as in some nuclear medicine tests, but only in small amounts. Thallium was once used as the main ingredient in rat poison and is currently used in electronics and optics. Bismuth also finds large application in pharmaceuticals, in cosmetics and in metallurgy.
Post-Transition Metals on Earth
Not only are some of these Periodic Table elements somewhat radioactive, but they are also harmful to our Earth’s biosphere. Gallium, Indium, and Tin are too rare and they don’t occur in their natural, free form on Earth. Bismuth and its ores can be found all over the Earth’s crust and they are twice as common as gold. Thallium can be extracted from minerals and other elements like Lead, Zinc and Copper. Lead is found in minerals (the most abundant and important Lead mineral is called galena), ores and other chemical elements, such as Zinc, Copper, Arsenic, Silver, and Gold.