By Ron B. Davis Jr., Georgetown University
Tin was well-known even in the ancient world. It is more abundant in the universe because, with an atomic number of 50, tin is one of only six naturally occurring elements with a magic number of protons. Beyond being very easy to obtain and work with, tin does not oxidize readily. This is why tin foil and tin cans became the first widely available metal containers for foods in the 19th century.
Combining with Oxygen
Tin’s chalcophilic character makes it abundant near Earth’s surface, along with other sulfur-loving elements. And its low position on the activity series ensured that tin would be accessible even to ancient peoples, who could easily smelt this element from its ore using charcoal fires.
When Dimitri Mendeleev first proposed his famous periodic table, he sorted elements based on the ratios in which various elements combine with oxygen and hydrogen.
This technique worked remarkably well for the alkali and alkaline earth metals, which combine in a 2:1 and 1:1 ratio with oxygen, respectively. We now know that those metals consistently combine with oxygen or hydrogen in a single ratio for each because they are so close to a perfect octet.
Forming Two Different Compounds
By contrast, quite a few of the p-block metals can combine with oxygen in more than one ratio.
Tin, is one such example. It commonly forms two different compounds with oxygen. One of these is a tin-to-oxygen ratio of 1:2, as one would expect for a member of the carbon group of the table. That’s called stannic oxide. But another tin compound, stannous oxide, contains tin and oxygen in a 1:1 ratio—a behavior more like a group 2 element, such as magnesium or calcium.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Achieving a True Octet
Atoms do indeed quest for octets—when possible. For elements like the p-block metals, losing electrons is usually the shortest path to that octet. However, they have to lose a lot of electrons to get there—four electrons in the case of tin. That means to achieve an octet, a tin atom needs to lose 4 electrons in order take on a net charge of +4. Building up that much charge takes a lot of energy!
Silicon dealt with this differently, forming covalent bonds to oxygen instead. But tin has a bigger electron cloud that makes it more metal than metalloid. So how does tin cope with being so far from a perfect octet?
Since successive loss of electrons requires the input of more and more energy, sometimes tin and other d-block metals make a compromise, settling just for a full s-subshell, rather than a full valence shell. When this happens, a charge of 2+ is formed. A true octet is not achieved, but a closed subshell and weaker charge can balance out this sacrifice.
Tin’s Melting Point
The low melting point makes tin, along with its neighbor indium, go-to elements in solder formulations. They have melting points that one can achieve with a soldering iron, yet form a rigid, solid connection between wires that they join.
But tin is also a borderline metal so weak that pure tin metal can easily disappoint. If one puts pure tin in a hot oven, expect it to melt at about 449° Fahrenheit.
Changing Physical Properties of Tin
Use of pure tin is further complicated by the fact that its physical properties can change, based on two allotropes. Both variants of tin are solids, but each has a different spatial arrangement of tin atoms within that solid. So-called ‘white tin’ is a shiny substance with metal-like properties. But then there’s ‘gray tin’, which is a more brittle substance.
Which arrangement the tin atoms choose depends mainly on temperature. Metallic white tin can transition to brittle gray tin when its temperature falls below just 56° F (13° C).
There’s a dramatic story often told about Napoleon Bonaparte’s attempted invasion of Russia to illustrate how a simple allotropic conversion might change history.
In June of 1812, Napoleon began his enormous invasion of Russia, marching the largest fighting force in the history of Europe at that time—the so-called ‘Grand Armee’—into Russian territory. During the hot summer months, the invasion appeared to be a success
And then winter came.
As winter descended on Russia, Napoleon’s army was forced to rely on an ever-less-reliable supply chain from the homeland in western Europe. But, as the story goes, Napoleon’s army may have also experienced the problem of shiny tin buttons on their uniforms and tin cooking utensils, ultimately crumbling to gray tin dust in the cold.
This is a believable story, since the Russian cold is more than enough to convert metallic white tin items to gray tin. The apparent object lesson here is to never get involved in a winter land war with p-block-metal buttons on the uniforms!
But was Napoleon really defeated because of his army’s tin buttons? Well, the conversion to brittle gray tin happens pretty slowly—and layer by layer, not all at once. And some historians question the claim that his army’s buttons were even made entirely or mostly of tin.
The principal reasons for Napolean’s defeat were almost certainly poor tactical decisions, combined with brutally cold weather and stout opposition from Russian forces. Nevertheless, the ‘tin buttons’ story is a colorful favorite of chemistry teachers, because it dramatizes a very real property of tin.
Common Questions about Napoleon’s Defeat and the Element Tin
Tin’s chalcophilic character makes it abundant near Earth’s surface, along with other sulfur-loving elements. And tin’s low position on the activity series ensured that tin would be accessible even to ancient peoples, who could easily smelt this element from its ore using charcoal fires.
Use of pure tin is complicated by the fact that its physical properties can change, based on two allotropes. Both variants of tin are solids, but each has a different spatial arrangement of tin atoms within that solid.
As the story goes, Napoleon Bonaparte’s army experienced the problem of shiny tin buttons on their uniforms and tin cooking utensils, ultimately crumbling to gray tin dust in the cold.