CHEM1902 Inorganic Chemistry
History of the Periodic Table
A number of elements (such as gold, silver and copper) have been
known from antiquity, as they can be found in their native form and
mined with primitive tools. However, the notion that
there was a limited number of elements from which everything was
composed originated with the Greek philosopher Aristotle, who around
330 BC proposed that everything is made up of a mixture of one
or more roots. Four roots were later renamed as elements
by Plato: earth, water, air and fire.
While Aristotle and Plato introduced the concept of an element,
their ideas did little to advance the understanding of the nature of matter.
The history of the periodic table is related to the
history of the discovery of the chemical elements. Clearly without a
set of elements there is no need to arrange them into a Table!
To help recall all the names of the elements, check out the
Periodic Table Song
and the original
Tom Lehrer 1967 version.
(Make sure you don't miss the section starting around the 2 minute mark!)
The discovery of the elements: from Antiquity to Middle Ages (13 elements),
Middle Ages to 1799 (21 elements), 1800 to 1849 (24 elements), 1850 to 1899
(26 elements), 1900 to 1949 (13 elements), 1950 to 1999 (16 elements) and
since 2000 (5 elements so far).
The first person in modern history to discover a new
element was the German,
Hennig Brandt. In 1649, after prolonged heating of
human urine, a glowing white substance resulted which he named phosphorus.
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 had 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.
Periodic Tables arrange the elements in order of a particular property, such as
atomic number or more historically, the atomic weight (now relative atomic mass).
Of the nearly 120 chemical elements now known, 80 are stable and one way
of grouping them has been in terms of whether they readily conduct electricity.
Metals conduct, nonmetals don't, and a small group, (the metalloids), have
intermediate properties and often behave as semiconductors.
The use of properties with numeric values was more useful than those such as
smell or colour. Before any Table could be produced, there needed to be data
to use and this was not readily available before 1860.
In that year, a conference was held in
Karlsruhe (Germany) and on the last day reprints of
Stanislao Cannizzaro's 1858 paper on atomic weights,
was distributed. This was the first reasonably accurate list of atomic
weights. Earlier values suffered from not only being inaccurate but faulty
reasoning based on guesses of valency had led to some being recorded as
only a fraction of their correct values.
In 1862, the French geologist
Alexandre Beguyer de Chancourtois (1820-1886)
was the first to list the known elements in order of increasing weight and this
was about 3 years before Newlands and 7 years before Mendeleev's Periodic
System was developed.
He drew the elements as a continuous spiral around a metal cylinder divided
into 16 parts. The atomic weight of oxygen was taken as 16 and was used
as the standard against which all the other elements were compared.
Tellurium was situated at the centre, and he named the device "vis tellurique",
or telluric screw.
A modern reproduction is shown on right.
Why then is
Mendeleev remembered and de Chancourtois forgotten?
Despite de Chancourtois' work, his publication attracted little attention from
chemists around the world. He presented the paper to the French Academy of
Sciences who published it in Comptes Rendus, the academy's journal.
However his original diagram was left out of the publication, making the paper
hard to comprehend. The diagram did eventually appear in a less widely read
geological pamphlet but this dealt mainly with geological concepts, and did
not suit the interests of many chemists.
In 1865, the English chemist
John Alexander Reina Newlands (1837-1898) classified the fifty-six
known elements into eleven groups, based on their physical properties.
His 'Law of octaves', stated that "any given element will exhibit
analogous behaviour to the eighth element following it in the table."
Newlands' arranged all of the known elements into seven groups, which
he likened to the octaves of music.
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, especially given the ridicule it provoked
from some of his colleagues. It is claimed that someone jokingly suggested
that placing the elements in alphabetical order might be just as meaningful.
The importance of Newlands' analysis was finally recognised by the Chemistry
Society with a Gold Medal, five years after they recognised Mendeleev's work.
The Russian chemist
Dmitri Ivanovich Mendeleev was the first scientist to make a periodic
table similar to the one used today. Like de Chancourtois and Newlands,
Mendeleev arranged the elements by atomic weight. It is sometimes said that
he played 'chemical solitaire' on long train journeys, using cards with various
facts about the known elements.
IUPAC recommended names for groups of elements in the periodic table.
|2||Alkaline earth metals
Charles Janet (1849-1932) periodic table is an interesting alternative
periodic table that organises elements according to orbital filling.
It differs from the standard table in placing the s-block elements on the
right, so that the subshells of the periodic table are arranged in the
order (n-3)s, (n-2)p, (n-1)d, nf from left to right. There is then no need
to interrupt the sequence or move the f block into a 'footnote'. He believed
that no elements heavier than number 120 would be found, so he did not
envisage a g block.
In the simple model of the structure of atoms, each element can be
considered to consist of a nucleus containing protons and neutrons and
surrounded by electrons. Protons and electrons are charged particles, but
neutrons have no charge. The relative masses are shown below:
||1.6726 x 10-24 g
||1.6749 x 10-24 g
||9.110 x 10-28 g
The mass of a proton and neutron are similar, while the mass of an electron is
approximately 2000 times lighter. From the number of protons, neutrons,
and electrons in any element, it is possible to calculate the mass of that element.
The lightest noble gas element is helium; it only contains two protons and two neutrons.
The expected mass is therefore = 2 * 1.0086654 + 2 * 1.0072766 + 2 * 0.000548597 = 4.0329799
This compares reasonably well with the known relative atomic mass of 4.002602
In the case of elements with isotopes then to calculate the relative atomic mass it is necessary to know
the percentage of each isotope and the number of neutrons in these isotopes.
For example, chlorine has two isotopes to consider, where the ratio of 35:37 is 75.77 % : 24.23 %
35Cl has 17 protons, 18 neutrons and 17 electrons and
the mass for this is 35.28899428 * 75.77 = 26.73847097
37Cl has 17 protons, 20 neutrons and 17 electrons and the mass for
this is 37.30632411 * 24.23 = 9.039322333
Combining these gives a mass of 35.7777933 which can be compared
to the accepted relative atomic mass of 35.45
The section of interest for Transition Metal Chemistry is shown below and
latest method from IUPAC for displaying isotopic information.
- The stable isotopic abundances are shown as pie diagrams
- Those elements whose standard atomic weight is not a constant of nature (i.e.
have more than 1 isotope whose abundance varies with location)
are presented as an interval within square brackets based on an assessment
of the lower and upper bounds. (pink background - no example for TM elements yet)
- Element (titanium) whose standard atomic weight is not a constant of nature and
whose standard atomic weight assessment has not been finalised is given as a
single value with an uncertainty that includes both measurement uncertainty
and uncertainty due to isotopic abundance variations (yellow background)
- Element (manganese) whose standard atomic weight is a constant of nature
because it has only one stable isotope. The standard atomic weight is given
as a single value with an IUPAC evaluated uncertainty (blue background)
- Element (technetium) has no stable isotopes and thus no standard
atomic weight. (white background)
Variation of IE, EA and E with Atomic Number is covered in
A free copy of the
Periodic Table Explorer can be downloaded from this link.
Free on-line edition of General Chemistry text
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The Department of Chemistry, University of the West Indies,
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