Hennig Brand[edit]

The history of the periodic table is also a history of

the discovery of the chemical elements. The first

person in history to discover a new element was

Hennig Brand, a bankrupt German merchant. Brand

tried to discover the Philosopher's Stone — a

mythical object that was supposed to turn

inexpensive base metals into gold. In 1649, his experiments with distilled human

urine resulted in the production of a glowing white substance, which he named

phosphorus.[3] He kept his discovery secret until 1680, when Robert Boyle

rediscovered phosphorus and published his findings. The discovery of phosphorus

helped to raise the question of what it meant for a substance to be an element.

In 1661, Boyle defined an element as "a substance that cannot be broken down

into a simpler substance by a chemical reaction". This simple definition served

for three centuries and lasted until the discovery of subatomic particles.

Antoine-Laurent de Lavoisier[edit]

Lavoisier's Traité Élémentaire de Chimie (Elementary Treatise of Chemistry),

which was written in 1789 and first translated into English by the writer Robert

Kerr, is considered to be the first modern textbook about chemistry. It contained

a list of "simple substances" that Lavoisier believed could not be broken down

further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc

and sulfur, which formed the basis for the modern list of elements. Lavoisier's list

also included 'light' and 'caloric', which at the time were believed to be material

substances. While many leading chemists refused to believe Lavoisier's new

revelations, the Elementary Treatise was written well enough to convince the

younger generation. However, Lavoisier's descriptions of his elements lack

completeness, as he only classified them as metals and non-metals.

19th century[edit]

Johann Wolfgang Döbereiner[edit]

In 1817, Johann Wolfgang Döbereiner began to formulate one of the earliest

attempts to classify the elements. In 1829, he found that he could form some of

the elements into groups of three, with the members each of group having

related properties. He termed these groups triads. Some of the triads that were

classified by Döbereiner are:

1 chlorine, bromine, and iodine

2 calcium, strontium, and barium

3 sulfur, selenium, and tellurium

4 lithium, sodium, and potassium

In all of the triads, the atomic weight of the middle element was almost exactly

the average of the atomic weights of the other two elements.[4]

Alexandre-Emile Béguyer de Chancourtois[edit]

Alexandre-Emile Béguyer de Chancourtois, a French geologist, was the first

person to notice the periodicity of the elements — similar elements occurring at

regular intervals when they are ordered by their atomic weights. He devised an

early form of periodic table, which he named Vis tellurique (the 'telluric helix'),

after the heaviest element in his diagram,tellurium.[5] With the elements arranged

in a spiral on a cylinder by order of increasing atomic weight, de Chancourtois

saw that elements with similar properties lined up vertically. His 1863 publication

included a chart (which contained ions and compounds, in addition to elements),

but his original paper in the Comptes Rendus Academie des Scéances used

geological rather than chemical terms and did not include a diagram. As a result,

de Chancourtois' ideas received little attention until after the work of Dmitri

Mendeleev had been publicised.[6]

John Newlands[edit]

Newlands' law of octaves

In 1865, the English chemist John Newlands classified the fifty-six known

elements into eleven groups, based on their physical properties. [7][8]

Newlands noted that many pairs of similar elements existed, which differed by

some multiple of eight in mass number, and was the first to assign them an

atomic number.[9] When his 'law of octaves' was printed in Chemistry News,

likening this periodicity of eights to the musical scale, it was ridiculed by some of

his contemporaries. His lecture to the Chemistry Society on 1 March 1866 was

not published, the Society defending their decision by saying that such

'theoretical' topics might be controversial.

The importance of Newlands' analysis was eventually recognised by the

Chemistry Society with a Gold Medal five years after they recognised

Mendeleev's work. It was not until the following century, with Gilbert N. Lewis'

valence bond theory (1916) and Irving Langmuir's octet theory of chemical

bonding (1919), that the importance of the periodicity of eight would be

accepted.[10][11] The Royal Chemistry Society acknowledged Newlands'

contribution to science in 2008, when they put a Blue Plaque on the house where

he was born, which described him as the "discoverer of the Periodic Law for the

chemical elements".[9]

Dimitri Mendeleev[edit]

Dmitri Ivanovich Mendeleev

Zeitschrift für Chemie (1869, pages 405-6), in which Mendeleev's periodic table is first

published outside Russia.

Mendeleev's 1871 periodic table. Dashes: unknown elements. Group I-VII: modern group 1–

2 and 3–7 with transition metals added; some of these extend into a group VIII. Noble

gasses unknown (and unpredicted).

The Russian chemist Dmitri Mendeleev was the first scientist to make a periodic

table similar to the one used today. Mendeleev arranged the elements by atomic

mass, corresponding to relative molar mass. It is sometimes said that he played

'chemical solitaire' on long train journeys, using cards with various facts about

the known elements.[12] On March 6, 1869, a formal presentation was made to the

Russian Chemical Society, entitled The Dependence Between the Properties of

the Atomic Weights of the Elements. In 1869, the table was published in an

obscure Russian journal and then republished in a German journal, Zeitschrift für

Chemie.[13] In it, Mendeleev stated that:

5 The elements, if arranged according to their atomic mass, exhibit an

apparent periodicity of properties.

6 Elements which are similar as regards to their chemical properties have

atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or

which increase regularly (e.g., K, Rb, Cs).

7 The arrangement of the elements, or of groups of elements in the order of

their atomic masses, corresponds to their so-called valencies, as well as, to

some extent, to their distinctive chemical properties; as is apparent among

other series in that of Li, Be, B, C, N, O, and F.

8 The elements which are the most widely diffused have small atomic

weights.

9 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.

10 We must expect the discovery of many yet unknown elements – for

example, elements analogous to aluminium and silicon – whose atomic weight

would be between 65 and 75.

11 The atomic weight of an element may sometimes be amended by a

knowledge of those of its contiguous elements. Thus the atomic weight of

tellurium must lie between 123 and 126, and cannot be 128.

12 Certain characteristic properties of elements can be foretold from their

atomic masses.

Scientific benefits of Mendeleev's table

It enabled Mendeleev to predict the discovery of new elements and left

spaces for them, namely eka-silicon (germanium), eka-aluminium (gallium),

and eka-boron (scandium). Thus, there was no disturbance in the periodic

table.

It could be used by Mendeleev to point out that some of the atomic

weights being used at the time were incorrect.

It provided for variance from atomic weight order.

Shortcomings of Mendeleev's table

The table was not able to predict the existence of the noble gases.

However, when this entire family of elements was discovered, Sir William

Ramsay was able to add them to the table as Group 0, without the basic

concept of the periodic table being disturbed.

A single position could not be assigned to hydrogen, which could be placed

in either the alkali metals group or in the halogens group.

Lothar Meyer[edit]

Unknown to Mendeleev, the German chemist Lothar Meyer was also working on a

periodic table. Although his work was published in 1864, and was done

independently of Mendeleev, few historians regard him as an equal co-creator of

the periodic table. Meyer's table only included twenty-eight elements, which were

not classified by atomic weight, but by valence and he never reached the idea of

predicting new elements and correcting atomic weights. A few months after

Mendeleev published his periodic table of the known elements, predicted new

elements to help complete his table and corrected the atomic weights of some of

the elements, Meyer published a virtually identical periodic table.

Meyer and Mendeleev are considered by some historians of science to be the co-

creators of the periodic table, but Mendeleev's accurate prediction of the

qualities of undiscovered elements enables him to have the larger share of the

credit.

William Odling[edit]

In 1864, the English chemist William Odling also drew up a table that was

remarkably similar to the table produced by Mendeleev. Odling overcame the

tellurium-iodine problem and even managed to get thallium, lead, mercury and

platinum into the right groups, which is something that Mendeleev failed to do at

his first attempt. Odling failed to achieve recognition, however, since it is

suspected that he, as Secretary of the Chemical Society of London, was

instrumental in discrediting Newlands' earlier work on the periodic table.

20th century[edit]

Henry Moseley[edit]

Henry Moseley

In 1914, a year before he was killed in action at Gallipoli, the English physicist

Henry Moseley found a relationship between the X-ray wavelength of an element

and its atomic number. He was then able to resequence the periodic table by

nuclear charge, rather than by atomic weight. Before this discovery, atomic

numbers were sequential numbers based on an element's atomic weight.

Moseley's discovery showed that atomic numbers were in fact based upon

experimental measurements.

Using information about their X-ray wavelengths, Moseley placed argon (with an

atomic number Z=18) before potassium (Z=19), despite the fact that argon's

atomic weight of 39.9 is greater than the atomic weight of potassium (39.1). The

new order was in agreement with the chemical properties of these elements,

since argon is a noble gas and potassium is an alkali metal. Similarly, Moseley

placed cobalt before nickel and was able to explain that telluriumoccurs before

iodine, without revising the experimental atomic weight of tellurium, as had been

proposed by Mendeleev.

Moseley's research showed that there were gaps in the periodic table at atomic

numbers 43 and 61, which are now known to be occupied by technetiumand

promethium respectively.

Glenn T. Seaborg[edit]

During his Manhattan Project research in 1943, Glenn T. Seaborg experienced

unexpected difficulties in isolating the elements americium and curium. Seaborg

wondered if these elements belonged to a different series, which would explain

why their chemical properties were different from what was expected. In 1945,

against the advice of colleagues, he proposed a significant change to

Mendeleev's table: the actinide series.

Seaborg's actinide concept of heavy element electronic structure, predicting that

the actinides form a transition series analogous to the rare earth series of

lanthanide elements, is now well accepted and included in the periodic table. The

actinide series is the second row of the f-block (5f series). In both the actinide

and lanthanide series, an inner electron shell is being filled. The actinide series

comprises the elements from actinium to lawrencium. Seaborg's subsequent

elaborations of the actinide concept theorized a series ofsuperheavy elements in

a transactinide series comprising elements from 104 to 121 and a superactinide

series of elements from 122 to 153.

In 1862, French geologist Alexandre-Emile Béguyer de Chancourtois listed the

elements on paper tape and wound them, spiral like, around a cylinder. Certain

‘threes’ of elements with similar properties came together down the cylinder. He

called his model the ‘telluric screw’.

In 1864, English chemist John Newlands

noticed that, if the elements were arranged

in order of atomic weight, there was a

periodic similarity every 8 elements. He

proposed his ‘law of octaves’ on this.

Image: Dmitri MendeleevIn 1869, Lothar Meyer complied a periodic

table of 56 elements based on a regular

repeating pattern of physical properties such

as molar volume. Once again, the elements

were arranged in order of increasing atomic

weights.

Image: William Ramsay

Image: Glenn Seaborg

Also in 1869, Russian chemist Dmitri

Mendeleev produced a periodic table based

on atomic weights but arranged

‘periodically’. Elements with similar

properties appeared under each other. Gaps

were left for yet to be discovered elements.

In 1894, William Ramsay discovered the

noble gases and realised that they

represented a new group in the periodic

table.

In 1914, Henry Moseley determined the

atomic number of each of the known

elements. He realised that, if the elements

were arranged in order of increasing atomic

number rather than atomic weight, they

gave a better fit within the ‘periodic table’.

In 1940, Glenn Seaborg artificially produced

heavy mass elements such as neptunium.

These new elements were part of a new

block of the periodic table called ‘actinides’.