Periodic Table
Dec 24, 2015
Lavoisier 1789
Traite Elementaire de Chimie.
Produced the first table of elements
Introduced a logical system for naming compoundsand helped introduce the metric system
May 8th 1794
Dalton, 1803, was the first chemist to use the term ‘atom’
He used this idea to explain how elements react together toform molecules.
Dalton suggested that it should be possible to compare the massesof atoms.
Hydrogen 1
Carbone 4.2
Oxygen 5.5
Water 6.5
Sulphur 14.4
Sulphuric Acid
25.4
Atomic Weights
Prout 1815
All atomic weights are multiples of Hydrogen and thatHydrogen is the fundamental element from which all other elements are formed.
However, it was found that atomic weightsare not whole numbers. E.g. Cl 35.46
More on atomic numbers
Dobëreiner 1817
Noticed that certain groups of 3 elements, e.g. Ca, Sr, Ba the atomic weight of 2nd was approximately the mean the 1st and 3rd.
Dobëreiner’s triads (5 in total)
Element Relative atomic mass
Calcium 40
Strontium 88
Barium 137
Element Relative atomic mass
Lithium 7
Sodium 23
Potassium 39
Béguyer de Chancourtois 1862
He also realised that when elements are arranged in order of their atomic weight there was a repeating pattern of elements at regular intervals.That this happens when there are multiplies of 8x the atomic weight of hydrogen.So he arranged them in a spiral around a vertical cylinder divided into 16 vertical sections.
Telluric Screw
Newlands
Element Atomic weights
Element Atomic Weights
Element Atomic Weights
Hydrogen
1 Fluorine 8 Chlorine 15
Lithium 2 Sodium 9 Potassium 16
Beryllium
3 Magnesium
10 Calcium 17
Boron 4 Aluminium 11 Chromium
18
Carbon 5 Silicon 12 Titanium 19
Nitrogen 6 Phosphorus
13 Manganese
20
Oxygen 7 Sulphur 14 Iron 21
Newlands in 1865, using Cannizzaro’s system (elements in order ofsuccession) of atomic weights noticed a pattern, noticed that the 8th one was a ‘kind of repetition of the 1st. He called this the ‘Law of Octaves’. OK for the first 15 or so elements
Meyer
ElementI
Atomic weights
ElementII
Atomic weights
ElementIII
Atomic Weights
B 11 Al 27.3
C 11.97 Si 28
N 14.01 P 30.9
O 15.96 S 31.98
F 19.1 Cl 35.38
Li 7.01 Na 22.99 K 39.04
?Be 9.3 Mg 23.9 Ca 39.9
Meyer in 1869, independently, put forward a similar list of elements.Meyer plotted an ‘atomic volume’ curve, showing that a quantitative property alternatively rises and falls over definite periods of the Elements.
Mendeleev 1871
Unlike Meyer, Mendeleyev believed in his convictions. In 1869 he published ‘Principles of Chemistry’
Mendeleev, without knowing about Meyer’s work, predicted as yet undiscovered elements. Meyer recognised Mendeleev’s work and both where awarded The Davy medal for Chemistry in 1882.
Mendeleyev 1871
period I II III IV V VI VII VII
1 H
2 Li Be B C N O F
3 NaK
MgCa
Al*
SiTi
PV
SCr
ClMn
Fe Co Ni
4 CuRb
ZnSr
*Y
*Zr
AsNb
SeMo
Br* Ru Rh Pd
5 Ag Cd In Sn Sb Te I
Mendeleev predicted the properties of this element, he called eka-silicon
Eka-Silicon
Property Prediction
Appearance Dark-grey
Relative Atomic mass
72
Density 5.5 g cm-3
Reaction with water
None
Reaction with alkali
More than with acid
Reaction with Acid Very little
Oxide Basic
Chloride Liquid, <100oC b.p.
Germanium
Property Germanium 1885
Appearance Dark-grey
Relative Atomic mass
73
Density 5.35 g cm-3
Reaction with water
None
Reaction with alkali
More than with acid
Reaction with Acid Very little
Oxide Basic
Chloride Liquid, <100oC b.p.
Mendeleev also predicted the properties of Gallium and Scandium
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. Of special importance was hydrogen, the original standard for atomic weights. 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, 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 (easierto do than with hydrogen)(They used this because 8 g of oxygen combine with 1 g hydrogen so 8 g of oxygen was equivalent to 1 g hydrogen.)
Relative Atomic Masses