TNPSC Free Notes Chemistry – Periodic Classification of elements Lavoisier Classification (1789)

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

Periodic Classification of elements

Lavoisier Classification (1789)
 Father of Modern Chemistry
 Classified Substances – 4 Groups
Acid-making elements
Sulphur, Phosphorous, Carbon
Gas-like elements
Oxygen, Hydrogen, Nitrogen, Light
Metallic elements
Gold, Silver, Tungsten, Iron
Earthy elements
Lime (Calcium Oxide), Magnesia (Magnesium Oxide), Silex (Silicon Di Oxide)
Dobereiner’s Triads
 In 1817, Johann Wolfgang Dobereiner, a German chemist, suggested a method of
grouping elements based on their relative atomic masses.
 He arranged the elements into groups containing three elements each. He called these
groups as ‘triads’ (tri – three).

 Dobereiner showed that when the three elements in a triad are arranged in the
ascending order of their atomic masses, the atomic mass of the middle element is nearly
the same as average of atomic masses of other two elements.

Limitation of Dobereiner’s Law
 Dobereiner could identify only three triads from the elements known at that time and
all elements could not be classified in the form of triads.
 The law was not applicable to elements having very low and very high atomic mass.
Newlands’ Law of Octaves
 In 1866, John Newlands arranged 56 known elements in the increasing order of their
atomic mass.
 He observed that every eighth element had properties similar to those of the first
element like the eighth note in an octave of music is similar to the first.
 This arrangement was known as ‘law of octaves
Limitations
 There are instances of two elements being fitted into the same slot, e.g. cobalt and
nickel.
 Some elements, totally dissimilar in their properties, were fitted into the same group.
 (Arrangement of Co, Ni, Pd, Pt and Ir in the row of halogens)
 The law of octaves was not valid for elements that had atomic masses higher than that
of calcium.
 Newlands’ table was restricted to only 56 elements and did not leave any room for new
elements.
 Discovery of inert gases (Neon. Argon….) at later stage made the 9th element similar to
the first one. Eg: Neon between Fluorine and Sodium.

Lother Meyer

 In 1868, Lother Meyer
 Physical Properties (Melting Point & Boiling Point)
 Atomic Volume
 Atomic Mass
Dimitri Mendeleev (1869)
The Properties of the element based on:
 Physical Properties
 Chemical Properties
 Increasing Atomic Mass
 Listed 70 known Elements

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