Feb. 7, 2017


Celebrating 154 years, since the beginning of the first table of the Elements…

Je Mari Williams announces first National Periodic Table Day Celebration!

Je Mari W.




  • Antoine Lavoisier, considered the Father of Chemistry Antoine Lavoisier, considered the Father of Chemistry Discovered that water is made from Hydrogen and Oxygen; air is made from Oxygen and Nitrogen. So water and air can't be elements because they are built from something simpler. Thus, he concluded that substances that decompose based on physcial change or chemical change are not elements. He developed a list of 33 elements into four "element" groups. (Mrs. Marie Lavoisier pictured with Antoine was his assistant) It is generally accepted that Lavoisier's great accomplishments in chemistry largely stem from his changing the science from a qualitative to a quantitative one. Lavoisier established the Law of Conservation of Mass, and chemistry became an exact science, one based on careful measurement. Lavoisier helped construct the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. He predicted the existence of silicon (1787) and was also the first to establish that sulfur was an element (1777) rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same. Sadly, he was executed by guillotine on May 8, 1794 during the French reign of terror.
  • Alexandre Béguyer de Chancourtois, created an atomic weights telluric screw table. Alexandre Béguyer de Chancourtois, created an atomic weights telluric screw table. He was the first person to list the known elements in order of increasing weight of their atoms. What are the problems with this method? First, it does not distinguish between the weights of atoms and of molecules. If a molecule of H2 is given a relative mass of 1 instead of 2, then when other elements are compared with it, their relative atomic masses are halved. Second, the term called equivalent, or combining weight defined the number of grams of an element that combined with 8 g of oxygen. Chemists used this because it is in general easier practically to measure the weight of an element that combines with oxygen than the weight that combines with hydrogen. For example the equivalent weight of carbon is 3 g, because 3 g of carbon combine with 8 g oxygen. The valency of carbon is 4 because it forms the compound methane, CH4. So the relative atomic mass of carbon is 3 x 4 = 12. However, sometimes an element was given the wrong valency. Thus beryllium, combining weight 4.6, was given the valency 3 because it was chemically similar to aluminium. This gave an atomic weight of 13.8, placing it between carbon and nitrogen where there was no space.
  • John Newlands, published first table of the Elements John Newlands, published first table of the Elements The English analytical chemist John Alexander Reina Newlands, b. Nov. 26, 1837, d. July 29, 1898, was one of the precursors of Dmitry Ivanovich Mendeleyev in formulating the concept of periodicity in the properties of the chemical elements. He was educated by his farther,then in 1856 he entered The Royal College Of Chemistry. There he studied for a year under August Hoffman. He then became assistant to J. T. Way, the Royal Agricultural Society's chemist. He showed that if the elements are arranged in the order of their atomic weights, those having consecutive numbers frequently either belong to the same group or occupy similar positions in different groups, and he pointed out that each eighth element starting from a given one is in this arrangement a kind of repetition of the first, like the eighth note of an octave in music.
  • Dmitri Ivanovich Mendeleev, formulated the Periodic Law The Russian periodic law chemist was born in Siberia in 1834. He first trained as a teacher in the Pedagogic Institute of St. Petersburg before earning an advanced degree in chemistry in 1856. He formulated the Periodic Law, created his own version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered. The chemical law that the properties of all the elements are periodic functions of their atomic weights was developed independently by two chemists: in 1869 by Dmitry Mendeleyev, a Russian, and in 1870 by Julius Lothar Meyer, of Germany. Although no element then known had an atomic weight between those of calcium and titanium, Mendeleyev left a vacant space for it in his table. This place was later assigned to the element scandium, discovered in 1879, which has properties justifying its position in the sequence. The discovery of scandium proved to be one of a series of dramatic verifications of the predictions based on the periodic law, and validation of the law accelerated the development of inorganic chemistry. Mendeleev also investigated the composition of petroleum, and helped to found the first oil refinery in Russia; element 101 is named after him. Dmitri Ivanovich Mendeleev, formulated the Periodic Law
  • Julius Lothar Meyer, classification of the Elements Julius Lothar Meyer, classification of the Elements The German periodic law chemist came from a medical family of Oldenburg, and first pursued a medical degree. In medical school he became interested in chemistry, especially physiological topics like gases in the blood. In the first edition of Die modernen Theorien der Chemie (1864), Meyer used atomic weights to arrange 28 elements into 6 families that bore similar chemical and physical characteristics, leaving a blank for an as-yet-undiscovered element. His one conceptual advance over his immediate predecessors was seeing valence, the number that represents the combining power of an atom of a particular element, as the link among members of each family of elements and as the pattern for the order in which the families were themselves organized. In his original scheme the valences of the succeeding families, beginning with the carbon group, were 4, 3, 2, 1, 1, and 2.
  • Amedeo Avogadro, hypothesized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Amedeo Avogadro, hypothesized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. As an example, equal volumes of molecular nitrogen and oxygen contain the same number of molecules when they are at the same temperature and pressure, and observe ideal gas behavior. In practice, real gases show small deviations from the ideal behavior and the law holds only approximately. The most significant consequence of Avogadro's law is that the ideal gas constant has the same value for all gases. Amedeo Avagadro was honored with the Avogadro constant, since he was the first to realize that the volume of a gas (strictly, of an ideal gas) is proportional to the number of atoms or molecules.
  • Joseph John Thomson, proposed first model of atom based on experiment. Joseph John Thomson, proposed first model of atom based on experiment. In 1897, he showed that cathode rays, radiation emitted in a low pressure glass tube when a voltage is applied between two metal plates, consist of particles, electrons that carry electricity. Nearly all German physicists of the time held that these visible rays were produced by occurrence in the ether—a weightless substance then thought to pervade all space—but that they were neither ordinary light nor the recently discovered X-rays. British and French physicists, on the other hand, believed that these rays were electrified particles. By applying an improved vacuum technique, Thomson was able to put forward a convincing argument that these rays were composed of particles. Furthermore, these rays seemed to be composed of the same particles, or corpuscles, regardless of what kind of gas carried the electric discharge or what kinds of metals were used as conductors. Thomson’s conclusion that the corpuscles were present in all kinds of matter was strengthened during the next three years when he found that corpuscles with the same properties could be produced in other ways—e.g., from hot metals.
  • Henry Moseley, determined the number of protons in an element. Henry Moseley, determined the number of protons in an element. He published the results of his measurements of the wavelengths of the X-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the X-ray emissions of the elements coincided with the ordering of the elements by atomic number. With the discovery of isotopes of the elements, it became apparent that atomic weight was not the significant player in the periodic law as Mendeleev, Meyers and others had proposed, but rather, the properties of the elements varied periodically with atomic number. Known as Moseley’s law, this fundamental discovery concerning atomic numbers was a milestone in advancing the knowledge of the atom. In 1914 Moseley published a paper in which he concluded that there were three unknown elements between aluminum and gold (there are, in fact, four). He also concluded correctly that there were only 92 elements up to and including uranium and 14 rare-earth elements.
  • Glenn T. Seaborg, proposed last major change to periodic table. Glenn T. Seaborg, proposed last major change to periodic table. Seaborg was the principal or co-discoverer of ten elements: plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium and element 106, which, while he was still living, was named seaborgium in his honor. He is best known for discovering the element plutonium with Edwin McMillan, in February 1941. Plutonium is the element that makes atomic bombs explode. Seaborg and his colleagues are responsible for the identification of more than 100 isotopes of elements throughout the Periodic Table. Into the 1930s the heaviest elements were being put up in the body of the periodic table, and Glenn Seaborg "plucked those out" while working with Fermi in Chicago, naming them the Actinide series, which later permitted proper placement of subsequently 'created' elements - the Transactinides, changing the periodic table yet again. These elements were shown separate from the main body of the table. Seaborg demonstrated that the heavy elements form a "transition" series of actinide elements in a manner analogous to the rare-earth series of lanthanide elements. The concept demonstrated how the heavy elements fit into the Periodic Table and thus demonstrated their relationships to the other elements.


national periodic table day

In 1649, the first element was discovered through scientific inquiry by Hennig Brand; that element was phosphorous (P). The first table of the elements was published by John Newlands in Chemical News Vol. 7, Feb. 7, 1863, pp. 70-72.  The goal of the table was to place the elements in a way to make chemical reaction prediction more reliable.   How did Alexandre Chancourtois, Lothar Meyer, Dmitri Mendeleev, and Henry Moseley influence the formation of the periodic table?  First, around 500 BC Pythagoras studied the musical scale and the ratios between the lengths of vibrating strings needed to produce them; he developed what may be the first completely mathematically based scale which resulted by considering intervals of the octave (a factor of 2 in frequency) and intervals of fifths (a factor of 3/2 in frequency). John Newlands based his table on the pattern associated with the octaves on a piano determined by Pythagoras; he called his periodic law the “Law of Octaves”. 

Because Newlands's use of a musical analogy in a chemical theory sounded like a regression to Pythagorean mysticism, the theory was ridiculed. Pythagorean philosophy states that numbers were the underlying substance of reality much in the way that Thales believe water to be origin of being in the universe. Pythagoreans were extremely superstitious and mystical. They believed that the human soul was trapped in a continuous cycle of death and reincarnation. It was taught that the only way to free ourselves from this cycle was to obtain a higher understanding of the universe through introspective thought and philosophical study. A central tenant of the Pythagorean belief system was the transmigration of the soul. This included the transmigration of human souls into the bodies of animals. It is perhaps for this reason that Pythagoras strictly forbid the consumption of meat, resulting in his followers becoming some of the earliest known vegetarians. Also, the Pythagoreans were forbidden to eat beans, since they believed that a human being lost a part of his or her soul whenever passing gas. Abstinence of the flesh was insisted upon. The upper class well educated scholar understood the down fall of this belief system, because the Pythagoreans attempted to pressure the ordinary citizens of Crotona into adopting their unique lifestyle. This, rather unfortunately, did not end well for the Pythagoreans. When the plain citizens were told that they must not eat beans and that they must, at all costs, abstain from eating meat, it was too much to bear. A general persecution of the Pythagoreans occurred. Many of the followers were killed or driven away. The Pythagorean meeting place was burned to the ground and Pythagoras was forced to flee with his followers around 480 BCE.

John Newlands table of the Elements first published February 7, 1863
  Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8
Period 1 H = 1 F = 8 Cl = 15 Co/Ni = 22 Br = 29 Pb = 36 I = 42 Pt/Ir = 50
Period 2 Li = 2 Na = 9 K = 16 Cu = 23 Rb = 30 Ag = 37 Cs = 44 Tl = 53
Period 3 Gl = 3 Mg = 10 Ca = 17 Zn = 25 Sr = 31 Cd = 34 Ba/V = 45 Pb = 54
Period 4 Bo = 4 Al = 11 Cr = 18 Y = 24 Ce/La =33 U = 40 Ta = 46 Th = 56
Period 5 C = 5 Si = 12 Ti = 19 In = 26 Zr = 32 Sn = 39 W = 47 Hg = 52
Period 6 N = 6 P = 13 Mn = 20 As = 27 Di/Mo = 34 Sb =41 Nb = 48 Bi = 55
Period 7 O = 7 S = 14 Fe = 21 Se = 28 Ro/Ru = 35 Te = 43 Au = 49 Os = 5

The first table of the elements can be compared to our origin, since children are not born adults; their birthday represents the starting point, and as the child grows into an adult these changes help us better understand progress; likewise the periodic table followed a similar pattern.  Why does the modern periodic table have 18 groups and 7 periods? The proton controls the look or appearance of the atom, since gold has 79 protons and platinum has 78 protons. So, why isn't the periodic table one long chain like an alphabet? The neutron controls the birth and death of the atom, when an atom decays into another the neutron number changes. The neutron is the main reason the periodic table took a lot of work to develop. Atoms can have different numbers of neutrons and are called isotopes. Atoms have a certain number of neutrons that make them stable and this is known as the band of stability. Thus the neutron is the reason Chancourtois and Mendeleev had very different periodic tables based on atomic weight. The electron is responsible for the structure of the modern periodic table. The electron controls behavior and elements are grouped based on behavior. The alkali and alkaline metals both form bases when placed in water. A base is an electron donor and hydrogen ion acceptor. The law of the octaves is the most important concept concerning the prediction of electron behavior. The behavior of the transition metals is determined by the law of the octaves associated with the predictable behavior of the nonmetals. The halogens seek to gain one electron to become stable and form a Nobel gas configuration. Thus the periodic table is structured based on the electron, and the law of the octaves is the backbone of the periodic table. Remove the law of the octaves and the predictable nature of the electron associated with electro negativity is lost and the periodic table loses its usefulness!

58years... Is the time it took to place Dalton's set of Atomic weight values in the first periodic table. In today's world of instant news and communication one might be shocked to know that it took a lot longer in the 1800's to discuss ideas with colleagues. Moreover, the telephone was invented in 1876 and this invention made it much easier to make progress on complex ideas. The atomic theory of matter, in its various forms, existed a good two thousand years before the time of John Dalton, he was the first to propose, in his 1808 book  A New System of Chemical Philosophy, that atoms had weight. Atoms, as Dalton defined them, were hard, solid, indivisible particles with no inner spaces, rather than something that could not be seen, touched, or tasted. They were indestructible and preserved their identities in all chemical reactions. Furthermore, each kind of element had its own specific kind of atom different from the atoms of other elements. These assumptions led him to propose that atoms were tangible matter and therefore had weight. In Dalton's first table published below progress can be observed compared to his 1808 table. He first records by experiment the mass of water to be 6.5 composed of Hydrogen 1 and Oxygen 5.5.



Hydrogen 1
Azot 4.2
Carbon 4.3
Ammonia 5.2
Oxygen 5.5
Water 6.5
Phosphorus 7.2
Phosphuretted hydrogen 8.2
Nitrous gas 9.3
Ether 9.6
Gaseous oxide of carbon 9.8
Nitrous oxide 13.7
Sulphur 14.4
Nitric acid 15.2
Sulphuretted hydrogen 15.4
Carbonic acid 15.3
Alcohol 15.1
Sulphureous acid 19.9
Sulphuric acid 25.4
Carburetted hydrogen from stagnant water 6.3
Olefiant gas 5.3

It was a challenge to develop the periodic table, and this is the first reason to celebrate its beginning.

Because atoms were much too small to be seen or measured by any common methods, absolute weights of atoms could not be determined. Rather, these first measurements were made by comparing weights of various atoms to hydrogen. Hydrogen was chosen as the unit of comparison because it was the lightest substance known and the weights of the other elements would be very close to whole numbers. Dalton's 1805 table of atomic masses was seriously deficient because he did not appreciate that atoms did not have to be in a one-to-one ratio; using more modern ideas, Dalton assumed, incorrectly, that all atoms had a valence of one (1). Thus, if the atomic mass of hydrogen is arbitrarily assigned to be 1, the atomic mass of oxygen is 8 on the Dalton scale.

The weight of oxygen could then be calculated because of earlier work by Humboldt and Gay-Lussac, who found that water consisted of only two elements, hydrogen and oxygen, and that there were eight parts of oxygen for every one part of hydrogen. Lacking any knowledge about how many atoms of hydrogen and oxygen combine in a molecule of water, Dalton again had to make some assumptions. He assumed that nature is basically very simple and, therefore, one atom of hydrogen combines with only one atom of oxygen. Using this hypothesis and the fact that hydrogen was assigned a weight of one unit, it follows that oxygen, which is eight times heavier than hydrogen, would have a weight of eight units. Of course, if the ratio between hydrogen and oxygen in water were not one to one, but some other ratio, the weight of oxygen would have to be adjusted accordingly. Dalton used experimental results and similar reasoning to prepare the very first Table of Atomic Weights, but because of the lack of knowledge about the real formulas for substances, many of the weights were incorrect and had to be modified later. His 1808 table records from experiment Oxygen with a value of 7 and Hydrogen with a value of 1, thus water would have 8 parts. Dalton, of course, was wrong, because a water molecule contains two atoms of hydrogen for every oxygen atom, so that the individual oxygen atom is eight times as heavy as two hydrogen atoms or sixteen times as heavy as a single hydrogen atom. 

Dalton's 1808 atomic weight table

Dalton table 1808

Dalton Example


Water is not easily separated and a current of electricity applied to a metal typically platinum result in the breaking of the hydrogen to oxygen polar covalent bond.  What was the faulty reasoning that led to inaccurate relative atomic masses (atomic weights)? There were two main faults. First chemists were not distinguishing between the weights of atoms and of molecules. Seven common elements exist as diatomic molecules (molecules containing two atoms, such as oxygen, O2), of special importance being hydrogen, the original standard for atomic weights. If amoleculeof H2is given a relative mass of 1 instead of 2, then when other elements are compared with it, their relative atomic masses are halved. 

Second, at the time chemists used a term called equivalent, or combining weight. This was the number of grams of an element that combined with 8 g of oxygen (They used this because 8 g of oxygen combine with 1 g hydrogen so 8 g of oxygen wasequivalentto 1 g hydrogen.) Chemists used this because it is in general easier practically to measure the weight of an element that combines with oxygen than the weight that combines with hydrogen. Atomic weights were then found from the equivalent weight using the relationship: 

Equivalent weight x valency = atomic weight 

where valency is the combining power of an element (the number of atoms of hydrogen that would combine with an atom of the element). 

For example the equivalent weight of carbon is 3 g, because 3 g of carbon combine with 8 g oxygen. The valency of carbon is 4 because it forms the compound methane, CH4. So the relative atomic mass of carbon is 3 x 4 = 12. 

Even when the equivalent weight was accurately determined, if the valency was wrong then a simple fraction of the correct atomic weight was obtained. (In the above example, if the valency of carbon was thought to be two, the value for carbon’s atomic weight would be 6.) The combining (or equivalent) weights were generally accurate but sometimes an element was given the wrong valency. Thus beryllium, combining weight 4.6, was given the valency 3 because it was chemically similar to aluminum. This gave an atomic weight of 13.8, placing it between carbon and nitrogen where there was no space. 

Many late 19th century chemists sought to determine the atomic weight of oxygen. Like most of them, Edward Morley focused on the reaction through which water is synthesized from hydrogen and oxygen, the two elements whose atomic weights he was comparing.
Because of the extreme technical difficulties of the required procedures, all other experimenters weighed only two of the three quantities involved in this reaction. Edward Keiser, professor of chemistry at Bryan Mawr College, based his determinations on the weight of hydrogen consumed and the water generated, whereas the distinguished physicist, Lord Rayleigh, weighed only the two gases and ignored the weight of the water. The two researchers obtained the weight of the third quantity by simple subtraction. They justified this procedure by assuming the conservation of matter, and, more importantly in this case, the absolute purity of all reactants and products. Morley avoided such assumptions. Though his technical innovations allowed him to obtain oxygen and hydrogen in purer states than had previously been possible, he correctly believed it necessary to weigh all three quantities in order to achieve the highest accuracy. His thoroughness provided two direct comparisons from which the atomic weight of oxygen could be calculated: hydrogen and water, and hydrogen and oxygen. And while Morley could not calculate atomic weights directly from the ratio of his measurement of oxygen and water—neither referred directly to hydrogen, his standard—he could, and did, use these numbers to check his other measurements.

In 1829 Johann Wolfgang Dobereiner discovered the existence of families of elements with similar chemical properties. Because there always seemed to be three elements in these families, he called them triads. In the table below the terms group and period have been added for comparison to the modern table. Dobereiner's triads can be found in the first group of the modern periodic table.

Dobereiner's Triads
  Group 1

Group 2

Group 3 Group 4 Group 5
Period 1 Li Ca S Cl Mn
Period 2 Na Sr Se Br Cr
Period 3 K Ba Te I Fe

Dobereiner also found that the atomic weight of the middle element in each triad is about equal to the average of the atomic weights of the first and third elements. The atomic weight of sodium (22.99 g/mol), for example, is remarkably close to the average of the atomic weights of lithium (6.94 g/mol) and potassium (39.10 g/mol). Dobereiner also found that the density of the middle element in most triads is roughly equal to the average of the densities of the other elements. The density of strontium (2.60 g/cm3), for example, is close to the average of the densities of calcium (1.55 g/cm3) and barium (3.51 g/cm3). Dobereiner noted that these elements reacted with water at room temperature, and recorded results that show the first group displayed the most similar chemical properties. They react with chlorine to form compounds with similar formulas: LiCl, NaCl, and KCl. They combine with hydrogen to form compounds with similar formulas: LiH, NaH, and KH. They form hydroxides with similar formulas: LiOH, NaOH, and KOH. However, he did not leave room for new elements, no chemical behavior could be predicted beyond the triads because a triad is limited to three, and no unknown element could be predicted based on the triad.

John Newlands discovered if he ordered the known elements by increasing atomic weights, the chemical properties of the elements would be similar for every eight groups. Ordering the elements by atomic weights produced a good starting point, however the atomic mass of Cobalt is greater than Nickel. Listing the elements in order of atomic mass places these two elements in the wrong group on the periodic table. Also, this is true with eight other elements as well and a reason the modern periodic table is not ordered by atomic mass.

piano octave

Newlands found that in this arrangement, the first and eighth elements are similar in their chemical and physical properties.


Notice Li is eight groups from Na, similar to F and Cl in that both show the same chemical and physical properties.

Like Stanisalo Cannizzaro, Newlands arranged the elements both in order of succession and in such a way as to get elements with similar characteristics on the same line of his table.  This resulted in some inaccuracies; nevertheless, Newlands defended his element table, stating that no other method for cataloging the elements was workable.  What justifies his element table as the starting point for the official periodic table?  The incompleteness of the table alluded to the possible existence of additional, undiscovered elements, such as the element Germanium, which was predicted by Newlands. The periodic table makes element prediction possible, thus Newlands’ prediction of the unknown element Germanium justifies his table of the elements as a starting point for the current periodic table. Newlands placed 5 elements in the correct family or group in his table of elements. Those correctly placed elements are as follows: Hydrogen, Lithium, Magnesium, Tellurium, and Iodine.  Also, he placed three of these elements in the correct periods within his table of the elements. 

Newlands’ table was initially dismissed by the English Chemical Society as irrelevant, because there are obvious problems with Newlands' table of the elements. The first row, for example, groups elements with similar chemical properties (such as F, Cl, Br, and I), but it also includes elements that have totally different chemical properties (such as Co, Ni, Pd, Pt, and Ir). Furthermore, at a time when elements were being discovered with some regularity, Newlands failed to leave room in his table for new elements. In a second table he grouped thirty-seven elements into ten classes, most of which contained one or more triads.  The incompleteness of the table was attributed to uncertainty regarding the properties of some of the more recently discovered elements and also to the possible existence of undiscovered elements. He considered Silicon (atomic weight 28) and Tin (atomic weight 118) to be the extremities of a triad, the middle term of which was unknown; thus his later claim to having predicted the existence of Germanium (atomic weight 73) before Mendeleev is valid.   On 1st March 1865, he described his ideas at a lecture at the Chemical Society (a forerunner of the Royal Society of Chemistry). The lack of spaces for undiscovered elements and the placing of two elements in one box were justifiably criticized, but an unfair suggestion from Professor Foster was that he might have equally well listed the elements alphabetically. Foster was on the Publication Committee which refused to publish his paper, supposedly because it was of a purely theoretical nature. Humiliated, Newlands went back to his work as chief chemist at a sugar factory.  Moreover, Newlands was so enthralled with this "law of octaves" that he made the mistake of trying to force the elements into this pattern. The hostile reception of his paper and the disinclination of the Society to publish it (on the grounds of its purely theoretical nature) seem to have discouraged Newlands from following up his ideas until after the publication of Mendeleev’s table in 1869. After that table appeared, Newlands continued to seek numerical relationships among atomic weights, while attempting, in a series of letters to Chemical News, to establish his priority. He set out his claims more specifically in December 1882, on hearing of the award of the Davy Medal of the Royal Society to Mendeleev and Lothar Meyer. His persistence was eventually rewarded in 1887, when the medal was awarded to him.  

Dmitri Mendeleev published his first periodic table in 1869 with many gaps and uncertainties.  This first table had 66 elements placed in 6 groups, 19 periods, and the 3 elements: hydrogen, lithium, and beryllium placed in the correct group. In the table below the terms group and period have been added for comparison to the modern table. Mendeleev organized the elements into rows and columns in his periodic table.

Periodic Table published by Dmitri Mendeleev in 1869
Group 1 Group 2 Group 3 Group 4 Group 5 Group 6
Period 1 Ti = 50 Zr = 90 ? = 180
Period 2 V = 51 Nb = 94 Ta = 182
Period 3 Cr = 52 Mo = 96 W = 186
Period 4 Mn = 55 Rb = 104.4 Pt = 197.4
Period 5 Fe = 56 Ru = 104.4 Ir = 198
Period 6 Ni / Co = 59 Pd = 106.6 Os = 199
Period 7 H = 1 Cu = 63.4 Ag = 108 Hg = 200
Period 8 Be = 9.4 Mg = 24 Zn = 65.2 Cd = 112
Period 9 B = 11 Al = 27.4 ? = 68 Ur = 116 Au = 197 ?
Period 10 C = 12 Si = 28 ? = 70 Sn = 118
Period 11 N = 14 P = 31 As = 75 Sb = 122 Bi = 210 ?
Period 12 O = 16 S = 32 Sc = 79.4 Te = 128 ?
Period 13 F = 19 Cl = 35.3 Br = 80 J = 127
Period 14 Li = 7 Na = 23 K = 39 Rb = 85.4 Cs = 133 Tl = 204
Period 15 Ca = 40 Sr = 87.6 Ba = 137 Pb = 207
Period 16 ? = 45 Ce = 92
Period 17 ? Er = 56 La = 94
Period 18 ? Yt = 60 Di = 95
Period 19 ? In = 75.6 Th = 118 ?  


Why would Dmitri Mendeleev be considered the father of the periodic table?  Mendeleev enjoyed playing the card game solitaire and arranged the cards containing information about each element on a table in order of ascending atomic weight grouping elements of similar properties together.  From this table, Mendeleev developed his statement of the periodic law and published his work on the Relationship of the Properties of the Elements to their Atomic Weightsin 1869. The advantage of Mendeleev's table over previous attempts was that it exhibited similarities not only in small units such as the triads, but showed similarities in an entire network of vertical, horizontal, and diagonal relationships. In 1906, Mendeleev came within one vote of being awarded the Nobel Prize for his work. 

In 1864, five years before the first announcement of a Periodic System by Mendeleev, Julius Lothar Meyer had produced a table of just 28 elements which he listed by their valence. [The term valence is now called valency and represents ‘combining power’ of an element. For example sodium forms a chloride NaCl and has a valency of one; magnesium forms MgCl2 and has a valency of two and so on.] The 28 elements were almost entirely main group elements. He incorporated transition metals in another table in 1868 which listed the elements in increasing weight order with elements with the same valence in a given column. This was earlier than Mendeleev's table (1869) but unfortunately Meyer's was not published until 1870.

Periodic Table according to Julius Lothar Meyer, 1870
  Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9
Period 1   B = 11.0 Al = 27.3       In = 113.4 Tl = 202.7  
Period 2                  
Period 3   C = 11.97 Si = 28       Sn = 117.8   Pb = 206.4
Period 4       Ti = 48   Zr = 89.7      

Period 5

  N = 14.01 P = 30.9   As = 74.9   Sb = 122.2   Bi = 207.5
Period 6       V = 51.2   Nb = 93.7   Ta = 182.2  
Period 7   O = 15.96 ? = 31.98   Se = 78   Te = 128    
Period 8       Cr = 52.4   Mo = 95.6   W = 183.5  
Period 9   F = 19.1 Cl = 35.38   Br = 79.75   J = 126.5    
Period 10       Mn = 54.8   Ru = 103.5   Os = 198.6  
Period 11       Fe = 55.9   Rh = 104.1   In = 196.7  
Period 12       Co/Ni = 58.6   Pd = 106.2   Pt = 196.7  
Period 13 Li = 7.01 Na = 22.99 K = 39.04   Rb = 85.2   Cs = 132.7    
Period 14       Cu = 63.3   Ag = 107.66   Au = 196.2  
Period 15 Be = 9.3 Mg = 23.9 Ca = 39.9   Sr = 87.0   Ba = 136.8    
Period 16       Zn = 64.9   Cd = 111.6   Hg =199.8  


 Mendeleev took a risk to suggest that new elements not yet discovered would be found to fill the blank places.  Also, he predicted the properties of the missing elements.  Many scientists greeted Mendeleev’s first periodic table with skepticism; however it’s predictive value that elements in the same column have similar properties soon became supported by the scientific community with the discovery of Gallium in 1875, of Scandium in 1879, and of Germanium in 1886. It is also worthy to note that Mendeleev's 1871 arrangement was related to the atomic ratios in which elements formed oxides, binary compounds with oxygen whereas today's periodic tables are arranged by increasing atomic numbers, that is, the number of protons a particular element contains. Although we can imply the formulas for oxides from today's periodic table, it is not explicitly stated as it was in Mendeleev's 1871 table. The oxides ratio column was not shown in earlier Mendeleev versions.  Mendeleev’s periodic table of 1871 contains eight groups and twelve periods and places 26 elements in their correct main group, thus providing evidence for Dmitri Mendeleev being the organizer of the periodic table of elements. 

Periodic Table published by Dmitri Mendeleev in 1871
Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8
Period 1 H = 1
Period 2 Li = 7 Be = 9.1 B = 11 C = 12 N = 14 O = 16 F = 19
Period 3 Na = 23 Mg = 24.4 Al = 27 Si = 28 P = 31 S = 32 Cl = 35.5
Period 4 K = 39.1 Ca = 40 ? = 44 Ti = 48.1 V = 51.2 Cr = 52.3 Mn = 55 Fe = 56, Ni = 58.5, Co = 59.1, Cu = 63.3
Period 5 (Cu) = 63.3 Zn = 65.4 ? = 68 ? = 72 As = 75 Se = 79 Br = 80
Period 6 Rb = 85.4 Sr = 87.5 Y = 89 Zr = 90.7 Nb = 94.2 Mo = 95.9 ? = 100 Rh = 103, Ru = 103.8, Pd = 108, Ag = 107.9
Period 7 (Ag) = 107.9 Cd = 112 In = 113.7 Sn = 118 Sb = 120.3 Te = 125.2 I = 126.9
Period 8 Cs = 132.9 Ba = 137 La = 138.5 Ce = 141.5 Di = 145
Period 9
Period 10 Yb = 173.2 Ta = 182.8 W = 184 Ir = 193.1, Pt = 194.8, Os = 200, Au = 196.7
Period 11 (Au) = 196.7 Hg = 200.4 Tl = 204.1 Pb = 206.9 Bi = 208
Period 12 Tb = 233.4 U = 239  


Even though the table has twelve periods, it is still impressive that it correctly places 26 elements in the same groups as seen on the modern periodic table.   

Next, Ernest Rutherford began his graduate work by studying the effect of x-rays on various materials. Shortly after the discovery of radioactivity, he turned to the study of the -particles emitted by uranium metal and its compounds.  One day, Hans Geiger suggested that a research project should be given to Ernest Marsden, who was working in Rutherford's laboratory. Rutherford responded, "Why not let him see whether any -particles can be scattered through a large angle?" When this experiment was done, Marsden found that a small fraction (perhaps 1 in 20,000) of the -particles were scattered through angles larger than 90o. Many years later, reflecting on his reaction to these results, Rutherford said: "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you." When he published the results of these experiments in 1911, Rutherford proposed a model for the structure of the atom that is still accepted today. He concluded that all of the positive charge and essentially all of the mass of the atom is concentrated in an infinitesimally small fraction of the total volume of the atom, which he called the nucleus.

In 1913, Henry Moseley observed and measured the X-ray spectra of various chemical elements that were found by the method of diffraction through crystals. This was a pioneering use of the method of X-ray spectroscopy in physics, using Bragg's diffraction law to determine the X-ray wavelengths. Moseley discovered a systematic mathematical relationship between the wavelengths of the X-rays produced and the atomic numbers of the metals that were used as the targets in X-ray tubes. This has become known as Moseley's Law, since he discovered a mathematical relationship between wavelengths of x-rays and the atomic number.  

Moseley's Law

Moseley X-ray


Charles Bury, an English chemist first used the word transition in 1921 when he referred to a transition series of elements during the change of an inner layer of electrons from a stable group of 8 to one of 18, or from 18 to 32.

H.G. Deming used the long periodic table in his textbook General Chemistry, which appeared in the USA for the first time in 1923 (Wiley), and designated the first two and the last five Main Groups with the notation "A", and the intervening Transition Groups with the notation "B".

The numeration was chosen so that the characteristic oxides of the B groups would correspond to those of the A groups. The iron, cobalt, and nickel groups were designated neither A nor B. The Noble Gas Group was originally attached (by Ueming) to the left side of the periodic table. The group was later switched to the right side and usually labeled as Group VlllA.

H.G. Deming - First Transition Group - Updated 1925

Deming 1925

Before Moseley's discovery, the elements were ordered based on the sequence of atomic masses, and modified when a pattern could not be justified.  Mendeleev had interchanged the orders of a few pairs of elements in order to put them in more appropriate places in this table of the elements. For example, the metals Cobalt and Nickel had been assigned the atomic numbers 27 and 28, respectively, based on their known chemical and physical properties, even though they have nearly the same atomic masses. In fact, the atomic mass of Cobalt is slightly larger than that of Nickel, which would have placed them in backwards order if they had been placed in the Periodic Table blindly according to atomic mass. Moseley's experiments in X-ray spectroscopy showed directly from their physics that Cobalt and Nickel have the different atomic numbers, 27 and 28, and that they are placed in the Periodic Table correctly by Moseley's objective measurements of their atomic numbers. 

Moseley's Periodic Table Published in 1930

Moseley Periodic Table 

Moseley showed that there were gaps in the atomic number sequence at numbers 43, 61, 72, and 75. These spaces are now known, respectively, to be the places of the radioactive synthetic elements Technetium and Promethium, and also the last two quite rare naturally-occurring stable elements Hafnium (discovered 1923) and Rhenium  (discovered 1925). Nothing about these four elements was known of in Moseley's lifetime, not even their very existence, thus he provided strong evidence that there were no other gaps in the Periodic Table between the elements with atomic number 13 and atomic number 79. 

Glenn T. Seaborg, born in 1912 in Michigan, he came to Los Angeles at the age of ten. After completing undergraduate studies in Chemistry at UCLA. The last major changes to the periodic table resulted from Glenn Seaborg's work. He reconfigured the periodic table by placing the actinide series below the lanthanide series.

Seaborg Periodic Table

Compare and Contrast

Antoine-Laurent Lavoisier produced the first modern list of chemical elements in 1789. Previously the metals except Mercury were not considered elements. Why does the list Lavoisier produced not represent the first periodic table of elements?

Antoine Lavoisier's classification of 33 elements into four element groups
Acid-making Elements Gas-like Elements Metallic Elements Earthy Elements
Sulphur Light Antimony Lime (calcium oxide)
Phosphorus Caloric (heat) Arsenic Magnesia (magnesium oxide)
Charcoal (carbon) Oxygen Bismuth Barytes (barium sulphate)
  Azote (Nitrogen) Cobalt Argilla (aluminium oxide)
  Hydrogen Copper Silex (silicon dioxide)
  Muriatic Radical Gold  
  Fluoric Radical Iron  
  Biracic Radical Lead  

The list that Lavoisier produced does not place the elements in a pattern that promotes chemical prediction. Lavoiser was not able to use his table to predict a missing element or predict element behavior. Elements are placed in groups based on similar chemical properties, thus Lavoisier's list does not support the starting point for the first periodic table.

Each element in the periodic table is placed in it's location based on atomic structure. All of the elements in a period have the same number of atomic orbital's. For example, every element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbital's for their electrons. As you move down the table, every row adds an orbital. At this time, there is a maximum of seven electron orbital's. 


Julius Lothar Meyer's first periodic table compared to that of John Newlands'.

In the first edition of Die modernen Theorien der Chemie (1864), Meyer used atomic weights to arrange 28 elements into 6 families that bore similar chemical and physical characteristics, leaving a blank for an as-yet-undiscovered element. His one conceptual advance over his immediate predecessors was seeing valence, the number that represents the combining power of an atom of a particular element, as the link among members of each family of elements and as the pattern for the order in which the families were themselves organized. In his original scheme the valences of the succeeding families, beginning with the carbon group, were 4, 3, 2, 1, 1, and 2.

Meyer's graph

It was not until 1870, however, that Meyer published his own table, a graph relating atomic volume and atomic number and clearly showing the periodic relationships of the elements. He did not claim priority for his achievement, and he admitted that he had been reluctant to predict the existence of undiscovered elements as Mendeleev had done. Meyer was just four years older than Mendeleev, and produced several Periodic Tables between 1864-1870.