History and Chemistry! Why would anybody link the two subjects together? Just as chemistry is important, the history of chemistry is equally important. The Berry Berry Teachers thinks that by learning and being concern about the history of chemistry, student will be able to get context of what they have learnt. So in this post, you’ll read all about the history of the periodic table. (Don’t worry, it is not as boring as it seems) Behold Berry Readers, presenting Part 1 of STPM Chemistry Form 6 notes on The Periodic Table. Read on how the periodic table is evolved until what it is today.
STPM Chemistry Form 6 Notes – Terminology and Concepts: The Periodic Table (Part 1)
The History of Periodic Table
Döbereiner: Döbereiner’s Triads
In 1817, Johann Wolfgang Döbereiner a German chemist (1780 – 1849) discovered that trends in certain properties of selected groups of elements and densities for some of these triads followed a similar pattern.
Newlands: Octave Law
In 1865, John Alexander Reina Newlands an English chemist (1837 – 1898) devised a Periodic Table of elements arranged in order of their relative atomic masses and name it law of octaves. Law of octaves states that “any given element will exhibit analogues behaviour to the eighth element following it in the table“.
Lothar Meyer: Atomic Volume of the Elements
In 1870, Julius Lothar Meyer a German chemist (1836-1907) described 28 elements and arranged the atomic volume (relative mass/density) of the elements against their relative atomic masses where similar chemical and physical properties are repeated at periodic intervals. Meyer presented a series of maxima and minima curve. At the peaks of the curve, Meyer discovered that the most electropositive elements appeared at the peak (Li, Na, K, Rb and Cs).
Mendeleev’s Periodic Table
In 1869, Dimitri Mendeleev a Russian chemist (1836 – 1907) published the periodic table of all known elements and predicted several new elements to complete the table that formed the basis of the modern Periodic Table. The elements were arranged into Periods (horizontal rows) and Groups (vertical columns). The arrangement of the elements in groups of elements is in the order of their atomic weights corresponds to their valences. Mendeleev predicted new elements, namely eka-silicon (germanium), eka-aluminium (gallium), and eka-boron (scandium).
Moseley: Proton Number
In 1914, Henry Gwyn Jeffrey Moseley an English physicist (1887 – 1915) discovered the relationship between an element’s X-ray wavelength and its atomic number (Z), Moseley demonstrated the arrangement by nuclear charge rather than related atomic mass. In Moseley’s experiment the fast moving electrons strike a solid anode. From it, an X-ray spectrum is produced. Through this, Moseley’s measurement of atomic numbers had an experimentally measurable basis and enable scientists to arrange the elements in the modern Periodic Table in order of increasing proton (atomic number).
That’s it for now on the history. Next part, you’ll learn about the long and short periods, the ‘spdf’ blocks, groups in the periodic table, atomic radius, ionic radius, electronegativity and ionisation energy of an atom. (Rather challenging, so make sure not to miss the next part only on Berry Berry Easy)