Post-Transition Metal

The post transition metals that are most commonly known to the people are aluminium, tin and lead. Otherwise known as the poor metals, they are found in groups 13, 14 and 15 on the periodic table. With lower melting and boiling points than transition metals, they are also softer and have higher electronegativity. However they have higher boiling points than the metalloids in the same row. Aluminium (the atomic number 13), gallium (the atomic number 31), thallium (the atomic number 81) are located in group 13, tin (the atomic number 50) and lead (the atomic number 82) are located in group 15, and finally bismuth (the atomic number 83) is placed in group 15.

Although aluminium (Al) is the most abundant metal in the Earth's crust, it is never find free in nature. All of the Earth's aluminium has combined with the other elements to form compounds. Two of the most common compounds are alum, such as potassium aluminium sulfate (KAl(SO4)2), and aluminium oxide (Al2O3). About 8.2% of the Earth's crust is composed of aluminium. The estimated crustal abundance is 8.23x104mg/kg and the estimated oceanic abundance is 2x10-3mg/kg. The number of stable isotopes is 1 and the oxidation state of aluminium is +3. Gallium (Ga) is soft, brittle metal that melts at only a few degrees above room temperature. Trace amounts of gallium are found in diaspore, sphalerite, germanite and bauxite. The estimated crustal abundance of gallium is 1.9x101mg/kg. There are 2 stable isotopes. The compounds of gallium have oxidation states +2 and +3 (rarely +1). Indium (In) is about as abundant as silver but it is much easier to recover since it typically occurs along with zinc, iron, lead and copper ores. The estimated crustal abundance is 2.5x10-1mg/kg and the estimated oceanic abundance is 2x10-2mg/kg. There is only 1 stable isotope. The compounds of indium have oxidation states +1, +2 and +3. Thallium (Tl) is found in the minerals crooksite (CuTlSe), lorandite (TlAsS2) and hutchinsonite ((PbTl)2As5S9), but it is usually obtained as a byproduct of the production of sulfuric acid or as a byproduct of refining zinc or lead. There are 2 stable isotopes. The compounds of thallium have oxidation states +1 and +3. The estimated crustal abundance is 8.5x10-1mg/kg and the estimated oceanic abundance is 1.9x10-5mg/kg. Tin (Sn) is primarily obtained from the mineral cassiterite (SnO2). Tin makes up only about 0.001% of the Earth's crust. Two allotropes of tin occur at the room temperature: gray and white. Tin has 8 stable isotopes and oxidation states +2 and +4. The estimated crustal abundance is 2.3mg/kg. Lead (Pb) has been known since ancients time. Lead may be found free in nature, but is usually obtained from the ores galena (PbS), anglesite (PbSO4), cerussite (PbCO3) and minium (Pb3O4). Lead makes up only about 0.0013% of the Earth's crust, but it is not considered as a rare element due to easily mined and refined. Lead has 3 stable isotopes and oxidation states +2 and +4. The estimated crustal abundance of lead is 1.4x101mg/kg and the estimated oceanic abundance is 3x10-5mg/kg. Bismuth (Bi) may be found free in nature and in such minerals as bismuthinite (Bi2S3) and bismite (Bi2O3). It has non stable isotopes and the oxidation states are +3 and +5. The estimated crustal abundance of bismuth is 8.5x10-3mg/kg.

‍

Physically, post-transition metals are soft (or brittle), have poor mechanical strength, melting points lower than those of transition metals; most also have boiling points lower than those of the transition metals. Being close to the metal-nonmetal border, their crystalline structures tend to show covalent or directional bonding effects, having generally greater complexity or fewer nearest neighbors than other metallic elements.

‍

Chemically, they are characterized by covalent bonding tendencies, acid-base amphoterism and the formation of anionic species such as aluminates, stannates and bismuthates (in the cas of aluminium, tin and bismuth, respectively).

‍

                                                      Aluminium foil

Aluminium is used in a huge variety of products including cans, foils, kitchen utensils, windows frames, beer kegs and aeroplane parts. This is because of its particular properties. It has low density, is non-toxic, has a high thermal conductivity, has excellent corrosion resistance and can be easily cast, machined and formed. Aluminium is non/magnetic and non-sparking. Gallium has a similar structure as silicon and is a useful silicon substitute for the electronics industry. It is an important component of many semiconductors. It is also used in red LEDs (light emitting diodes) because of its ability to convert electricity to light. Tin has many uses. It takes a high polish and is used to coat other metals to prevent corrosion, such as in tin cans, which are made of tin-coated steel. Tin alloys are important, such as soft solder, pewter, bronze and phosphor bronze. The niobium-tin alloys are used for superconducting magnets. Most window glass is made by floating molten glass on molten tin to produce a flat surface. Tin salts sprayed onto glass are used to produce electrically conductive coatings. Lead, easily worked and corrosion resistant metal has been used for pipes, pewter and paint since Roman times. It has been used for insecticides, hair dyes and as an anti-knocking additive for petrol. All these uses have now been banned due to lead's bad influence to human health. Lead is still widely used for car batteries, pigments, ammunition, cable sheathing, weight for lifting, lead crystal glass, radiation protection. It is often use to store corrosive liquids.

‍

Watch these videos:

https://youtu.be/ZpQkgM0msj4

https://www.youtube.com/watch?v=LaaORZ0ofCY  

‍