Periodic Properties Test - 4

Mendeleev arranged the elements on the basis of their increasing atomic masses.
He stated the periodic law as: Properties of elements are periodic functions of their atomic masses.
Hence, option (2) is correct.
Note: While arranging the elements in the increasing order of their masses, he gave priority to the similarity in the formulae of oxides and hydrides.

The discovery of isotopes presented a major challenge to Mendeleev's periodic law.
Since Mendeleev's periodic law was based on atomic masses of the elements, the isotopes should have been placed in different slots despite the fact that they represent the same element.
This was a major disadvantage as the position of isotopes in Mendeleev's periodic table could not be justified.

Elements in the same group have similar electronic configurations.
The have the same number of electrons in the valence shell.
C: [He] 2s² 2p²
N: [He] 2s² 2p³
Carbon with four valence electrons belongs to the group 14.
Nitrogen with five valence electrons belongs to the group 15.

The elements of the same group of the periodic table have the same number of valence electrons.
Hence, they have the same valency and exhibit similar chemical properties.
e.g. All elements of the group 1 have valence shell configuration: ns¹

The modern periodic law states that the properties of elements are periodic functions of their atomic numbers.
This implies that when elements are arranged in the increasing order of their atomic numbers, the properties repeat periodically.

The numbers of periods and groups in the long form of periodic table are 7 and 18, respectively.

Alkali metals belong to the group 1 in the s-block of the periodic table as they have the valence shell configuration, ns¹.

Out of all the actinides, thorium and uranium occur naturally in substantial, primordial quantities and small amounts of persisting natural plutonium have also been identified. The radioactive decay of uranium produces transient amounts of actinium and protactinium. The atoms of neptunium, americium, curium, berkelium and californium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements.

Atomic radii of elements decrease gradually from left to right because new electrons are added into the same shell and the effective nuclear charge increases across the period.