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Chemistry
for Secondary Schools
Newlands noticed that an element tends to display characteristics similar to
the 8 element in front of it. He arranged the elements in columns according
th
to a law he called the Law of Octaves (Table 2.2). However, his classification
was unfortunate since he grouped together certain elements which had different
characteristics. For example, oxygen (O) was placed in the same group as iron
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(Fe) and sulfur (S). Newlands’ ideas were therefore rejected by many scientists.
Table 2.2: Newlands’ octaves of elements
H Li Be B C N O
F Na Mg Al Si P S
Cl K Ca Cr Ti Mn Fe
A Russian chemist, Dimitri Mendeleev, later improved Newlands’ ideas and
convinced other chemists to use them. He intended to illustrate recurring trends
(periodic trends) in the properties of elements. In 1869, Mendeleev summarised
his Periodic Law which states that the properties of elements are a periodic
function of their relative atomic masses. He arranged elements according to their
increasing atomic masses and by the similarity of properties. This resulted in an
early version of the periodic table of elements (Table 2.3). A vertical column of
elements is called a group and a horizontal row is called a period. He, however, left
gaps in the table predicting that there were existing elements yet to be discovered.
Table 2.3: Part of Mendeleev’s periodic table
Group
1 2 3 4 5 6 7 8
Period
1 H
2 Li Be B C N O F
3 Na Mg Al Si P S Cl
4 K Ca ̶ Ti V Cr Mn Fe, Co, Ni
5 Cu Zn ̶ ̶ As Se Br
Modern periodic table
The modern periodic table is a systematic arrangement of elements in order of
increasing atomic numbers. It is a result of several modifications to Mendeleev’s
periodic table as new elements were discovered and scientific theories advanced
to explain the chemical behaviour of elements. Unlike Mendeleev’s Periodic
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