By Ron B. Davis Jr., Georgetown University
Let’s look at when humans first began to discover and understand each element of the periodic table. The periodic table is much more than just a reference tool for chemists. If one looks closely at the table’s evolution, one will find that the names, symbols, positions of elements, and even the shape of the table itself have all changed in various ways.
Discovery of Elements
During our prehistory, humans probably knew of at least three elements: copper, carbon, and sulfur. Silver and gold likely became part of human life by around 5000 BC. Around 3000 BC, the widespread use of iron ushered in what we call the ‘Iron Age’. These elements were later joined by tin, then antimony, then mercury, and then lead, rounding out perhaps a dozen elements that were known by 1000 BC.
More than two thousand years would pass before the widespread understanding of additional elements developed. Zinc, for example, had been noticed by the ancient Romans. But only around 1100 AD did zinc begin to be refined in India. Similarly, arsenic compounds were noticed in copper ores for thousands of years before the outright discovery of elemental arsenic that is usually credited to a medieval alchemist around 1250.
In the 1400s, the heavy metal bismuth was noticed as distinct from lead, just in time to be alloyed with lead to make cast-type for the printing press. Phosphorus was discovered in 1669, by an alchemist who thought he’d found the ‘philosopher’s stone’ for turning other elements into gold. But it was only in the 1700s that the modern questing for what we now recognize as elements really began—and took off!
By 1776, the number of known elements (23) was double of what it had been for the ancient world. By 1800, known elements (33) were already triple the number known to the ancient world. By 1870, when the first periodic table appeared, we had over five dozen elements (62). And by the start of the 20th century, we had almost seven dozen elements in hand (83). By 1950, all naturally-occurring elements had been discovered. And in the most recent decades, humans have gone on to create twenty additional elements that have never been found in nature at all.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Early Version of the Periodic Table
When the periodic table was first created by Dmitri Mendeleev, the arrangement of the elements on the periodic table looked like a monthly wall calendar, where rows depict weeks and columns depict days of the week.
In the periodic table, the rows are called ‘periods’, and the columns are called ‘groups’. Unlike the modern periodic table, Mendeleev’s own periodic tables from more than a century ago had nearly uniform periods of the same size, making it look more rectangular than today’s version of the table.
However, as scientists continued to learn more about the elements—what they are made of, how atoms are structured, and what gives them their unique properties —the table’s shape evolved into the familiar, more complex shape we see today.
Modern Periodic Table
Today’s table is a map of atomic structure. As atoms become larger and larger, these larger atoms have more layers of sub-structure. Mapping this more complex atomic structure creates the need for more columns of elements to maintain periodicity in the table.
The four blocks we see on the modern table give us a map of how all atoms are structured. This is why the top rows, which contain the smallest, and simplest, of the elements, have fewer members than rows below them.
In fact, the sixth and seventh rows of the periodic table contain so many elements, with such complex atomic structures, that we can’t even fit them all in one run! Here, we typically see two series of elements moved out of line, beneath the rest of the table.
Think about how Alaska and Hawaii appear on a lot of US maps—often in separate boxes at the bottom. This is merely to save space. In reality, putting Alaska and Hawaii where they belong requires taking a much wider view, which can sometimes be impractical.
The same kind of space-saving is typically used for portions of the bottom two rows of the periodic table. When we put all these elements in their proper place, it becomes clear that rows 6 and 7 actually have 32 elements per period!
A Well-organized Menu
The periodic table is a road map to the elements, grouping those with similar properties close together. For example, the ‘Metals’ start on the far left and stretch past the center. Classic coinage metals, copper, silver and gold are all neighbors on the table. So are the notoriously toxic heavy metals, mercury, thallium, and lead. ‘Non-metals’ are sorted together on the right.
As we travel from the metals to the nonmetals, there are elements with intermediate properties, like ‘weak metals’ and ‘metalloids’. The radioactive elements thorium, uranium, and plutonium that helped to usher in the nuclear age are tucked close to one another on a single, very long row of entirely radioactive elements at the bottom of the table.
Groupings like these help us to determine which elements might be useful for any given purpose. It lets us make all sorts of predictions about the matter, even about substances that have yet to be discovered. It’s an astonishingly well-organized menu for all the ordinary matter that makes up our universe.
Common Questions about the Evolution of the Periodic Table
About a dozen elements were known by 1000 BC. These included copper, carbon, sulfur, silver, gold, iron, tin, antimony, mercury, and lead.
When the periodic table was first created by Dmitry Mendeleev, it looked similar to the monthly wall calendar in which the columns show the days and the rows show the weeks. In the periodic table, the rows are called ‘periods’, and the columns are called ‘groups’. Mendeleev’s periodic table was more rectangular than today’s version of the table.
The modern periodic table is a roadmap for different chemical elements, grouping the elements based on their properties. These groupings help to determine which elements can be useful for what purposes. The table also allows making a variety of predictions about the matter, even substances that have not yet been discovered.