Test: Genesis of Periodic Classification (May 7) - NEET MCQ

Even though each atom has more electrons as you move from left to right across the periodic table, the atomic radius decreases. The reason is that you're also adding more protons, which exert a stronger attractive force on the electrons, drawing them in a tiny bit closer. Ionic radius also decreases, although not for the exact same reason.

The first periodic law stated by Mendeleev was, "the physical and chemical properties of the elements are a periodic function of their atomic weights (atomic masses)." The elements having similar properties appeared in the same group (vertical column).

Newland's Law of octaves stated that if elements (known at Newland's time) were arranged in increasing order of their atomic weights, every eighth element had properties similar to the first element. For example, Li and Na have similar properties.

• Mendeleev arranged the elements in order of their atomic masses while taking chemical properties into consideration.
• He left gaps predicting that some elements will be discovered later.
• When inert gases were discovered, they could be placed in a new group without disturbing his existing table.

Since statement A states that groups 7 and 8 were arranged on the basis of equivalent weights, it stands incorrect. 

In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.

As you move down a periodic table group, electronegativity decreases because the distance between the atomic nucleus and the valence electrons increases.

• There are a total of 7 periods in the periodic table.
• The sixth period of the periodic table contains 32 elements.
• It is beginning with cesium and ends with radon.
• Lead (Pb) is currently the last stable element whereas all subsequent elements are radioactive.

• In 1829, Johann Dobereiner, a German scientist made some groups of three elements each and called them triads.
• He observed that the atomic mass of the middle element of a triad was nearly equal to the arithmetic mean of the atomic masses of the other two elements. 
• All three elements of a triad were similar in their properties.

The periodic table of today owes its development to two chemists namely the Russian chemist Dmitri Mendeleev and the German chemist J. Lother Meyer. In 1869, they independently proposed that when the elements are arranged in the increasing order of their atomic weights, similarities in physical and chemical properties appear at regular intervals.

There are several ways to tell metals and nonmetals apart. Nonmetalsdon't have a metallic appearance. Unlike metals, they typically have lower melting and boiling points and tend not to conduct heat or electricity very well.