By Ron B. Davis Jr., Georgetown University
Thallium, lead, and bismuth have truly huge nuclei compared to the other p-block metals. This means that these elements tend to be relatively rare in the universe. Elements in this region of the periodic table can only form naturally in the supernova explosions of big stars, or as the decay products of the primordial radioactive elements, thorium and uranium, which also formed in exploding stars.
Heaviest Stable Nucleus
Of these elements, lead is special for several reasons, not the least of which is that lead has the heaviest stable nucleus ever discovered. Lead has a magic number of 82 protons, and that helps to give lead four stable isotopes. Its relatively high nuclear stability makes primordial lead more common in our universe than any other element in row six of the table, including those with smaller nuclei like platinum, gold, or mercury.
Because lead has the heaviest stable nucleus possible, it finds itself as the final destination for virtually every radioactive decay chain associated with uranium or thorium. It has been estimated that the amount of lead Earth contains has actually increased by about 1% over the 4.5 billion years since our Earth formed, thanks to the radioactive decay of larger elements.
Easier to Find and Use
Many p-block metals have remarkably low melting points or softness compared to metals in the d-block of the periodic table. It is this softness and low melting points of p-block metals like tin and lead that have made them easier to find and use, even in ancient times. Evidence of their long relationship with humanity is enshrined on the table by their chemical symbols, which are based their ancient Latin names—stannum and plumbum.
Lead was a material of choice for the construction of plumbing systems as early as ancient Rome and as recently as the 1900s. In fact, the Latin name, plumbum, is also the origin of the modern English word plumbing.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Lead Poisoning
Much like its smaller cousin tin—lead is a ‘sulfur-loving’ element, which made it more abundant in Earth’s crust. This made it easy to collect, and a low melting point makes it easy to work with. These properties have made lead useful in many products, such as enhancing the durability and color of paints, or making glass more workable and durable.
Unfortunately, lead is also a poison, whose effects are cumulative, meaning long-term, steady exposure can cause real health problems. Lead poisoning—also known as plumbism—can cause life-long health problems, and this is why many products using lead are heavily restricted or even banned.
Thallium Poisoning
Lead’s neighbor to the left, thallium, is another toxic heavy metal. Thallium was named for the beautiful green glow it emitted during flame ionization tests when it was first discovered in 1861.
Like the other larger p-block metals, thallium is a chalcophile, and, therefore, more abundant in the Earth’s crust than most precious metals.
Unlike the slow-acting toxic effects of lead, thallium poisoning can be rapid, severe, and often deadly. Agatha Christie wrote a detective story in 1961 that brought wide attention to the fact that thallium’s deadly effects can resemble illness, and might be used to get away with murder. Thallium’s quick action also made it the active substance in rat poison for many decades until it was banned over safety concerns in the 1970s.
Bismuth
Given the hazards of thallium and lead, it’s surprising that bismuth, lead’s even heavier neighbor to the right, has almost no known toxicity.
Metallic bismuth is famous for its tendency to form beautiful cubic crystals with a multicolored sheen produced by a layer of its oxide. But bismuth is yet another weak metal that can occasionally behave more like a metalloid or nonmetal in compounds.
Just like the metalloid antimony, bismuth can form discrete molecules in combination with nonmetals, like bismuth chloride (butter of bismuth). This kind of bonding behavior is also observed in the over-the-counter medication bismuth subsalicylate, sold as Pepto-Bismol. In this compound, bismuth acts more like the smaller group-15 elements, such as nitrogen, forming three bonds to the nonmetal element oxygen.
In 2003, a group of French physicists discovered that what had been thought to be bismuth’s one stable isotope, bismuth-209, instead has a half-life life that is one billion times the age of the universe so far! This decay is so slow that bismuth-209 is generally considered safe.
Common Questions about the Heavier P-Block Metals: Lead, Thallium, and Bismuth
Unfortunately, lead is also a poison, whose effects are cumulative, meaning long-term, steady exposure can cause real health problems. Lead poisoning—also known as plumbism—can cause life-long health problems, and this is why many products using lead are heavily restricted or even banned.
Unlike the slow-acting toxic effects of lead, thallium poisoning can be rapid, severe, and often deadly. Agatha Christie wrote a detective story in 1961 that brought wide attention to the fact that thallium’s deadly effects can resemble illness, and might be used to get away with murder.
Metallic bismuth is famous for its tendency to form beautiful cubic crystals with a multi-colored sheen produced by a layer of its oxide. But bismuth is yet another weak metal that can occasionally behave more like a metalloid or nonmetal in compounds.
