By Ron B. Davis Jr., Georgetown University
Iron, despite being the twenty-sixth element in the periodic table, is the sixth most abundant in the cosmos—due to its remarkable position at the pinnacle of the nuclear binding energy curve. And given the way our early solar system sorted the heavier, metallic elements into the planets near the Sun, Earth is actually an ‘Iron Planet’, as it is as the single most abundant element making up the Earth.
Generating Planetary Magnetic Field
We only see a small fraction of the Earth’s iron at the surface, as its significant density caused most of it to sink into the core as the Earth cooled 4 billion years ago.
Most of the iron in our planet is concealed deep within its core, where it generates the planetary magnetic field that protects Earth’s inhabitants from deadly cosmic rays. But there is so much iron in our planet overall that it is the fourth most abundant element in the Earth’s crust.
Influence on Human History
Iron’s profound influence on human history is also inarguable.
Iron has been known to humankind since pre-history. Artifacts suggest that iron was used as early as 3000 BCE by ancient Egyptians, and its introduction to society created such profound impacts that it has come to be the namesake for an entire epoch in human history—the so-called Iron Age.
‘Iron’ is an Anglo-Saxon-derived name dating back as far as the Crusades. But its symbol, ‘Fe’ pays homage to an even older name in Latin. Though no longer used to refer to iron itself, the name ferrum does inspire modern chemical references to element 26, such as the iron oxide mineral ferrite or the property of ferromagnetism.
A Blank Canvas for Metallurgists
In its pure form, iron is a relatively soft metal that reacts slowly with both oxygen and acids. Pure iron left in the atmosphere will eventually become iron oxide, which is a brittle red material that most of us know as rust.
So why is a soft, brittle material that oxidizes, so sought-after? Well, for starters pure iron is relatively easy to obtain. And while pure iron itself is not the most ideal of building materials, when combined with other elements, such as carbon, boron, or many of the early transition metals, the properties of iron can be modified for the better.
In this way, we can think of iron as a blank canvas for metallurgists to practice their art and create a vast array of alloy materials that we rely on every day.
An Important Biological Role
Iron also has tremendously important biological roles, too. Perhaps the most well-known of these is its crucial function in the transport of oxygen at the center of a haemoglobin molecule. The iron in our haemoglobin is encircled by an organic molecule to create a substance called ‘heme’.
This heme is itself wrapped in a protein that helps finely tune the chemistry of iron to grab onto oxygen molecules in the lungs, move through our bloodstream, and then release the oxygen where it is needed in our body.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
The Iron Triad
As remarkable and irreplaceable an element as iron is, it does share properties with some of its neighboring elements on the periodic table: most notably, cobalt and nickel to its right—all of which appeared together in Mendeleev’s group VIII.
Like iron, cobalt and nickel both have partially filled 3D subshells in their ground-state electron configurations. Collectively, this group of three elements—iron, cobalt and nickel—is sometimes referred to as the ‘Iron Triad’. It is a reference to Dobereiner’s system of placing elements into groups of three—even though these elements share a common row, rather than a vertical group
Although cobalt and nickel’s names as ‘goblin-and-devil’ were born of disappointment by copper-prospecting miners, these elements actually have a number of properties that make them a great thing to have in their own right.
Relatively Resistant to Corrosion
Iron, cobalt, and nickel all appear—in that order—near the middle of the activity series. Because of this, they are easily obtained, but also relatively resistant to corrosion. All three of these metals will oxidize in the air over time, but the process is slow enough that they remain very useful to us as elemental metals.
In fact, nickel’s relatively good corrosion resistance has made it a metal of choice for electroplating of other, more-active metals to protect them from oxidation for long periods of time.
Magnetic properties are another remarkable similarity within this triad. Iron, cobalt, and nickel are three of just a handful of elements that exhibit the property, named for iron, known as ferromagnetism.
Many metals are attracted to magnetic fields, and can temporarily behave like a magnet while exposed to electricity or magnetism. But ferromagnetic materials are special, as they retain magnetic properties even when they are not exposed to a magnetic field. This ability to persist as a ‘permanent’ magnet is especially important in the case of iron and nickel, as they make up the vast majority of the Earth’s outer core.
It is there, at a depth of 1800 miles, or 2900 kilometers below the surface, where convection currents cause hot, liquid iron and nickel to slowly swirl about. The motion of those liquid metals, iron and nickel, deep in the Earth act as a geo-dynamo, creating the global magnetic field that protects our planet from cosmic-ray bombardment and helped early explorers to navigate the globe.
So, whether it is producing our planet’s magnetic field, producing building materials or supporting life, iron is an indispensable element in many ways. It’s a good thing we’ve got so much of it!
Common Questions about Iron, an Indispensable Element
We only see a small fraction of Earth’s iron at the surface because its significant density caused most of it to sink into the core as the Earth cooled 4 billion years ago.
Collectively, the group of three elements—iron, cobalt and nickel—is sometimes referred to as the ‘Iron Triad‘.
The motion of liquid metals, iron and nickel, deep in the Earth act as a geo-dynamo, creating the global magnetic field that protects our planet from cosmic-ray bombardment and helped early explorers to navigate the globe.