CHEM1902 Inorganic Chemistry

From Wikipedia 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.
Periodic Table -metals

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.

1st Periodic Table 1st Periodic Table
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.

Mendeleev Periodic Table 1869

IUPAC recommended names for groups of elements in the periodic table.
Group number Recommended name
1Alkali metals
2Alkaline earth metals
15Pnictogens
16Chalcogens
17Halogens
18Noble gases

The 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.

Charles Janet Periodic Table (~1930)
f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 p1 p2 p3 p4 p5 p6 s1 s2
1
H		 2
He
1
H		 2
He		 3
Li		 4
Be
5
B		 6
C		 7
N		 8
O		 9
F		 10
Ne		 11
Na		 12
Mg
13
Al		 14
Si		 15
P		 16
S		 17
Cl		 18
Ar		 19
K		 20
Ca
21
Sc		 22
Ti		 23
V		 24
Cr		 25
Mn		 26
Fe		 27
Co		 28
Ni		 29
Cu		 30
Zn		 31
Ga		 32
Ge		 33
As		 34
Se		 35
Br		 36
Kr		 37
Rb		 38
Sr
39
Y		 40
Zr		 41
Nb		 42
Mo		 43
Tc		 44
Ru		 45
Rh		 46
Pd		 47
Ag		 48
Cd		 49
In		 50
Sn		 51
Sb		 52
Te		 53
I		 54
Xe		 55
Cs		 56
Ba
57
La		 58
Ce		 59
Pr		 60
Nd		 61
Pm		 62
Sm		 63
Eu		 64
Gd		 65
Tb		 66
Dy		 67
Ho		 68
Er		 69
Tm		 70
Yb		 71
Lu		 72
Hf		 73
Ta		 74
W		 75
Re		 76
Os		 77
Ir		 78
Pt		 79
Au		 80
Hg		 81
Tl		 82
Pb		 83
Bi		 84
Po		 85
At		 86
Rn		 87
Fr		 88
Ra
89
Ac		 90
Th		 91
Pa		 92
U		 93
Np		 94
Pu		 95
Am		 96
Cm		 97
Bk		 98
Cf		 99
Es		 100
Fm		 101
Md		 102
No		 103
Lr		 104
Rf		 105
Db		 106
Sg		 107
Bh		 108
Hs		 109
Mt		 110
Ds		 111
Rg		 112
Cn		 113
Uut		 114
Fl		 115
Uup		 116
Lv		 117
Uus		 118
Uuo		 119
Uue		 120
Ubn
Lanthanide Actinide Transition metal Post-transition metal Metalloid Polyatomic nonmetal Diatomic nonmetal Noble gas Alkali metal Alkaline earth metal unknown chemical properties unknown

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:

Particle Charge Mass (g) Mass (amu)
Proton +1 1.6726 x 10-24 g 1.0072766
Neutron 0 1.6749 x 10-24 g 1.0086654
Electron -1 9.110 x 10-28 g 0.000548597

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

IUPAC periodic table
The section of interest for Transition Metal Chemistry is shown below and features the latest method from IUPAC for displaying isotopic information.
section of Periodic Table


Variation of IE, EA and E with Atomic Number is covered in periodic trends.

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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