Page 132 - Chemistry ICSE Class IX

120 ICSE Chemistry – 9

ASSIGNMENT 1

Dobereiner’s triads, Newlands’ law of octaves

ϭ͘ EĂŵĞ ƚŚĞ ĞůĞŵĞŶƚƐ ǁŚŝĐŚ ĨŽƌŵ ŽďĞƌĞŝŶĞƌ͛Ɛ ƚƌŝĂĚƐ͘
Ϯ͘ tŚĂƚ ǁĂƐ ƚŚĞ ďĂƐŝƐ ŽĨ ŽďĞƌĞŝŶĞƌ͛Ɛ ĐůĂƐƐŝĮĐĂƟŽŶ͍
ϯ͘ tŚĂƚ ŝƐ EĞǁůĂŶĚƐ͛ ůĂǁ ŽĨ ŽĐƚĂǀĞƐ͍
ϰ͘ tŚĂƚ ĂƌĞ ƚŚĞ ůŝŵŝƚĂƟŽŶƐ ŽĨ EĞǁůĂŶĚƐ͛ ůĂǁ ŽĨ ŽĐƚĂǀĞƐ͍

Mendeleev’s Periodic Law

The Russian chemist D’mitri Ivanovich Mendeleev studied the chemical
properties of all the 63 elements and their compounds known at that time.
From the observed similarities, he postulated the periodic law commonly
called as the Mendeleev’s periodic law.

What is Mendeleev’s periodic law

Gallium When Mendeleev arranged elements in the order of increasing atomic
masses, he observed that the elements with similar properties appeared at
regular intervals. This led him to state his famous periodic law in 1869. The
Mendeleev’s Periodic Law states that

“Properties of the elements are a periodic function of their atomic
masses.”
While working on this classi cation of elements, he wrote,
“— When I arrange the elements according to the magnitude of their
atomic masses beginning with the smallest, it becomes evident that there exists
a kind of periodicity in their properties. I designate by the name ‘Periodic Law’,
D’mitri Ivanovich Mendeleev
(1839–1907) the mutual relation between the properties of the elements and their atomic
masses. These relations are applicable to all the elements and have the nature
͛ŵŝƚƌŝ /͘ DĞŶĚĞůĞĞǀ͕ ƚŚĞ LJŽƵŶŐĞƐƚ
ŽĨ Ă ĨĂŵŝůLJ ŽĨ ƐĞǀĞŶƚĞĞŶ͕ ǁĂƐ ďŽƌŶ of a periodic function.”
ŝŶ ^ŝďĞƌŝĂ ;ZƵƐƐŝĂͿ͘ DĞŶĚĞůĞĞǀ
ǁĂƐ ǀĞƌƐĂƟůĞ ŐĞŶŝƵƐ͘ ,Ğ ŝŶǀĞŶƚĞĚ
ĂŶ ĂĐĐƵƌĂƚĞ ďĂƌŽŵĞƚĞƌ͘ ,ŝƐ ŵŽƐƚ Mendeleev’s Periodic Table
ŝŵĂŐŝŶĂƟǀĞ ĂŶĚ ďƌŝůůŝĂŶƚ ĐŽŶƚƌŝďƵƟŽŶ
ƚŽ ĐŚĞŵŝƐƚƌLJ ǁĂƐ ƚŚĞ ƉĞƌŝŽĚŝĐ When Mendeleev arranged elements in the order of increasing atomic
ĂƌƌĂŶŐĞŵĞŶƚ ŽĨ ƚŚĞ ĞůĞŵĞŶƚƐ ŝŶ ƚŚĞ masses, he obtained a chart consisting of vertical columns and horizontal
ĨŽƌŵ ŽĨ Ă ƚĂďůĞ͘ rows. He called this chart Periodic Table. This periodic table is commonly
known as the Mendeleev’s periodic table. The periodic table based on the
periodic law suggested by Mendeleev is shown in Table 5.2.
DĞŶĚĞůĞĞǀ ƵƐĞĚ Arabic numerals Mendeleev laid more stress on similarity in the properties of the
ƚŽ ŝĚĞŶƟĨLJ ƚŚĞ periods ĂŶĚ Roman elements. The order of increasing atomic masses was not strictly followed.
numerals ƚŽ ŝĚĞŶƟĨLJ ƚŚĞ groups͘
Thus, when an element did not seem to t into the expected position, he
left a gap for it. He predicted that new elements would ll these gaps as
and when discovered.
DĞŶĚĞůĞĞǀ͛Ɛ ƉĞƌŝŽĚŝĐ ƚĂďůĞ ĚŝĚ ŶŽƚ
ŝŶĐůƵĚĞ ƚŚĞ noble gases ďĞĐĂƵƐĞ What are the essential features of Mendeleev’s periodic
ƚŚĞƐĞ ŐĂƐĞƐ ;Žƌ ĞůĞŵĞŶƚƐͿ ǁĞƌĞ ŶŽƚ
ŬŶŽǁŶĂƚƚŚĂƚƟŵĞ͘ table
Mendeleev’s periodic table had the following essential features:
ƒ The vertical columns were called groups and the horizontal rows
were called periods.