The periodic table is, to put it simply, a method of organizing all of the elements currently known to science based on their sizes, electron configurations, and chemical properties.
Contrary to popular belief, Dmitri Mendeleev, often cited as the 'father' of the periodic table, was not the first to produce a table. Its current form is, in fact, the culmination of the work of many scientists throughout the ages.
In the following article, we'll take a whistle-stop tour of the major events in history that have contributed to the modern periodic table.
As this article is more about the history of the table than explaining the science of it, you can watch this video to get an introduction to the periodicity of elements.
There would be no periodic table without elements
Before any actual attempt to arrange elements was made, budding 'organizers' needed to figure out what they were organizing and just how many there are.
Metals like Gold, Tin, Copper, Lead, Mercury, and Silver have been known since antiquity but it would take the Renaissance to make the first true scientific discovery of the substances we now call elements.
It is widely acknowledged that the first scientifically identified, technically isolated element was phosphorous. This discovery was made during the 17th Century by Henning Brand, many more would soon follow.
Henning was a bankrupt German merchant who managed to isolate the element whilst trying to create the fabled Philosopher's Stone. At this time many people were experimenting with Alchemy with the ultimate goal of turning base metals to gold.
He would keep his discovery to himself until 1680 until Robert Boyle 'rediscovered' the element and unveiled it to the scientific world.
Boyle had previously proffered a definition for these new 'elements' as:-
"those primitive and simple Bodies of which the mixt ones are said to be composed, and into which they are ultimately resolved."
Over the next few hundred years, early chemists would gather a large body of knowledge about the properties of elements and their compounds.
By the year 1869, a grand total of 63 elements had been found. Scientists were beginning to notice some patterns emerge about the properties of these elements.
And so methods of classification for these elements began in earnest.
Lavoisier's the Elementary Treatise of Chemistry laid the groundwork
In 1789, Antoine-Laurent de Lavoisier wrote and published his groundbreaking Traité Élémentaire de Chimie (Elementary Treatise of Chemistry). This was later translated into English by Robert Kerr.
Both the original and translation are widely considered to be the first true Chemistry textbook. Within his seminal work, Lavoisier defined an element as a substance that cannot be broken down into a simpler substance via a chemical reaction.
It would be a definition that would be used for over a century until the discovery of subatomic particles.
Lavoisier's book contained a comprehensive list of these "simple substances" that would form the basis for our modern list of elements.
His list classified the elements into metal and non-metal. His system was resisted by his peers but was quickly adopted by the next generation of scientists. Lavoisier's system would, in time, prove to be inadequate, as it only used these two classifications.
The law of the triads takes us one step closer
As early chemists began to experiment with and make notes of properties of elements some interesting observations would soon be made.
William Prout, an English physician, and chemist made the important observation that atomic weights seemed to be multiples of that of Hydrogen in 1815. This would later become known as Prout's hypothesis and it would pave the way for later investigations into atomic weight and atomic theory.
A few years later in one major advancement towards the periodic table occurred.
Johann Dobereiner, in 1817, soon noticed that the atomic weight of Strontium was somewhere between that of Calcium and Barium.
These elements also had some similar chemical properties, as it turned out.
A bit later, in 1829, he would devise his 'Law of the Triads'. He observed that groups of elements like Chlorine, Bromine, and Iodine (The so-called Halogen "Salt-Forming" Triad) and Lithium, Sodium and Potassium (the so-called Alkali [forming] Metal triad) shared similar chemical properties.
Johann noted that the middle element in these 'Triads' had properties that were the average of the other two when ordered by atomic weight. He believed this might just be a universal law of nature.
He defined them as "Chemically analogous elements arranged in increasing order of their atomic weights formed well-marked groups of three called Triads in which the atomic weight of the middle element was found to be generally the arithmetic mean of the atomic weight of the other two elements in the triad."
This law became very popular amongst his peers at the time. Between 1829 and 1858 many notable scientists soon found the chemical relationships of these triads did actually extend beyond them.
During this period:-
-Fluorine was added to the halogen group,
-Oxygen, Sulfur, Selenium, and Tellurium were grouped together,
-Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth were likewise grouped together.
Great strides were seemingly being made but there was a problem. Research into this field was seriously hampered by accurate values and some were not often available.
Chancourtois' first attempt at a periodic table
A French geologist, Alexandre-Emile Béguyer de Chancourtois, is widely recognized as the first person to truly notice the periodicity of elements. For this reason, his compiled table built around this observation should probably be recognized as the very first periodic table of elements.
He noted that elements showed similar properties when ordered by atomic weights. His Vis Tellunque (Telluric Helix) was thus published in 1862. The name comes from the element Tellurium which fell near the center of his diagram.
His 'table' arranged the elements in a spiral within a cylinder in order of atomic weight. This cylinder was constructed so that 16 mass units could be written on it per turn. This way closely related elements lined up vertically.
This led him to propose that "the properties of the elements are the properties of numbers". He would be the first person to recognize that elemental properties seem to re-occur every seven elements.
Using his chart he even predicted the stoichiometry of several metallic oxides. Unfortunately for Chancourtois, he included ions and compounds within his chart as well as some geological, rather than chemical, terminology.
For this reason, his idea never really took off at the time. His work was also only realized after Mendeleev publicized his table a few years later.
From triads to octaves with John Newlands
The next big development towards the modern periodic table came in 1863 with John Newlands' Law of Octaves.
John, an English Chemist, published his paper classifying 62 established elements in 11 groups. This grouping, like his predecessors, was based on them having similar physical properties. He also noted that many pairs of similar elements' atomic weights seemed to change by multiples of 8.
In 1864-5 he took this further and published his own version of the periodic table whilst simultaneously proposing his Law of Octaves. John's law stated that any given element exhibits similar behaviors to the eight elements following it in the table.
His table thus organized the existing elements into 8 groups. John's table was also the first to display each elements atomic number.
Newland's Law of Octaves was met with some ridicule by his peers, in part because of the musical scale reference of the law. His situation wasn't helped when The Chemistry Society also failed to print his lecture from the 1st March 1866 on the subject.
Sadly his insight was only later appreciated five years after Mendeleev's table was printed by the very same Chemistry Society. It would also take another 50 years or so for the significance of the periodicity of eight was rediscovered when Valence Bond Theory (1916) and the Octet Theory of Chemical Bonding (1919) were devised.
He would later be honored with a blue plaque in 2008 on his old place of residence by The Royal Chemistry Society. It is perhaps a small consolation that he had, in his lifetime, officially entered the term "periodic" into the Chemistry lexicon.
Just who was the 'father' of the periodic table?
As far as the periodic table had come, it wasn't until Russian chemist Dmitri Mendeleev that the one we are familiar with today was formulated. Or so the commonly told story goes.
In fact, there is some disagreement about who actually deserves the honorific of title of 'the Father of the Periodic Table'. For some, it was clearly Mendeleev but there are those who argue that at least equal recognition should go to German Lothar Meyer. Both these men created very similar tables at, more or less, the same time.
Meyer published his 1864 textbook, Modern Theories of Chemistry, with an abbreviated version of the periodic table within it. It consisted of only around half of the then known elements which were listed in order of their valence.
It also, by virtue of this ordering, demonstrated periodic valance change as weight increased. He was never able to predict new elements using his table, critically Mendeleev was.
He expanded on this in 1868 which he gave to a peer for review prior to publication. Sadly for Meyer, Mendeleev published his more comprehensive table in 1869 a full year before he finally appeared in print in 1870.
Mendeleev's table would ultimately win out over that of Meyer. But, most importantly, Mendeleev's system was able to satisfactorily predict the qualities of unknown elements. For this reason alone, he is widely given more credit as being the 'father' of the periodic table when compared to Meyer.
Mendeleev: The undisputed 'father' of the periodic table
Dmitri Mendeleev, a Russian chemist, was the first to produce a periodic table similar to the one most of us are familiar with today. Like others before him, he arranged elements by atomic mass.
He, it is said, devised his table by playing a form of 'chemical solitaire' whilst on long train journeys. Each card was a single element with various facts and figures like the chemical symbol, atomic weight and other chemical and physical properties compiled on it.
When Mendeleev arranged the cards on a table, in order of ascending atomic weight, a clear grouping of elements of similar properties became abundantly clear. Thus his now famous table was born.
Using this as his inspiration, Mendeleev published his seminal work On the Relationship of the Properties of the Elements to their Atomic Weights in 1869.
In this publication, he made the following observations:-
-The elements exhibit a periodicity of properties when ordered by atomic mass,
-Elements with similar chemical properties have atomic weights of similar value or increase regularly,
-Ordering by weight also corresponds with their co-called valency,
-Elements that are widely diffused tend to be smaller atoms,
-The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body,
-There are some, as yet, undiscovered elements,
-An element's atomic weight of some elements appears to be wrong and should be amended e.g. Tellerium should actually be between 123 and 126 (not 128 as it was then),
-From their atomic masses, you can make some predictions about the elements chemical properties.
The great advantage of his table over its predecessors was the fact that it revealed patterns in elements in small units, like Triads, but also in larger vertical, horizontal and diagonal relationships between them. Sadly, he lost out by a single vote to win the Nobel prize for his contribution to Chemistry.
His table wasn't without its problems, however. Although he did leave gaps for yet to find elements he completely failed to predict the existence of the Noble Gases. William Ramsey had little problem fitting them in later on though, it should be noted.
Hydrogen also proved to be problematic. It could be placed in either the Alkali Metals groups, the Halogens or completely separately at the top of the table.
Other groups like the Lanthanides were very difficult to place into the existing table format. Polonium and Radium, found by Marie Curie in 1898, were also hard to fit into the table.
Mendeleev's table even predicted new elements
Another great discovery that Mendeleev made was his observation that previously determined atomic weights were not always accurate. His table, at times, needed him to reorder elements seemingly in breach of the premise of a consequential increase in atomic weights.
A good example was Beryllium. Its atomic weight was accepted to be 14 at the time but something didn't seem right, its chemical properties didn't fit the overall pattern.
He determined that it must have an atomic weight more like 9. He also placed it into Group 2 above Magnesium whose chemical properties were more similar than its previous position above Nitrogen.
In this manner, he would find that 17 elements needed to be moved into new positions from original ones when simply ordered by atomic weight. Even after he was shown to be correct about many of these elements, once their weight was reassessed, some needed to be placed out of weight order on the table, like Argon for example.
Once all known elements were assembled in this manner, some clear gaps appeared. These, Mendeleev realized, were places for as yet undiscovered elements.
A few of these, which he called eka-Aluminum, eka-Boron, and eka-Silicon would later be called Gallium, Scandium, and Germanium. They fitted his predictions quite comfortably.
Even today new elements are being found and added to the periodic table.
In total, Mendeleev was able to predict the future discovery of 10 new elements. Seven of there were eventually found but three atomic weights, 45, 146 and 175 either don't exist or are yet to be discovered.
Interestingly another man, William Odling, drew a similar table in 1864 to that of Mendeleev. He managed to overcome the Tellurium-Iodine problem and successfully placed Thallium, Lead, Mercury and Platinum into the right groups - something Mendeleev failed to do on his first attempt.
Odling never received any recognition for his work because he was the Secretary of the Chemical Society of London which led to accusations of plagiarism. Plus, he was instrumental in discrediting Newlands' earlier periodic table.
The troublesome Noble Gases stir things up and Moseley orders by atomic number
Lord Rayleigh, in 1895, discovered and reported that he had found a new gaseous element that seemed to be chemically inert. It was called Argon and it didn't logically fit into Mendeleev's existing table.
Three years later William Ramsey suggested that perhaps Argon should be placed between Chlorine and Potassium in a family with Helium. This despite Argon having an atomic weight greater than Potassium.
Ramsey termed the group the "Zero" group as they had a zero valency, hence their inertness. He also accurately predicted the future discovery of an element we now call Neon.
Today we call them the Noble Gases. Ramsey's work was further supported by the groundbreaking work of Henry Moseley.
His work using X-rays to study atomic structure would lead to a more accurate positioning of elements in the table. Tragically Henry would later be killed fighting on the far-flung beaches of the Gallipoli peninsula (Gelibolu in Turkish) in 1915.
To this very day, elements are now ordered by atomic number, (number of protons in the nucleus) rather than atomic weight thanks to Moseley's work. This also cleared up a lot of perceived 'problems' with ordered elements by atomic weight, much to the relief of chemists.
The Actinides and Lanthanides are added to the periodic table
The last significant changes to the periodic table of elements were conducted by Glenn T. Seaborg. This occurred during his research at the Manhattan Project in 1943.
He had some difficulty isolating the elements Americium and Curium and wondered if they might belong to a different series than currently placed. He, against the advice of his colleagues, decided to propose a change to Mendeleev's table by adding the Actinide series.
He also, through his research discovered all the transuranium elements from 94 to 102.
These new elements needed to be fitted into the existing table and so he reconfigured it by placing the Actinide series below the Lanthanide series of elements. A practice widely accepted today and represented on modern periodic tables.
He (and his colleagues) were also able to identify more than 100 isotopes of other elements on the table. They were also able to theorize a series of superheavy elements from 104 to 121 (now largely identified) and a superactinide series of elements from 122 to 153.
For this, he was awarded the Nobel Prize in Physics. Element 106, Seaborgium (Sg) was also named in his honor.
As we can see the periodic table, though usually credited to Dmitri Mendeleev is actually the culmination of centuries of incremental experimentation and discovery. Despite this, it would be improper to strip him of the honorific of the 'father' of the table.
Although he wasn't technically the first, Mendeleev's table was the first best attempt to organize the known elements. It was also able to make some predictions that would prove correct in time.
And so, the modern periodic table is, therefore, the combined knowledge of great scientific minds whose origin is almost as old as Chemistry itself.