Question

State the trends in the physical and chemical properties of elements in the modern
periodic table

Answer 1

Answer:

The periodic trends are based on the Periodic Law, which states that if the chemical elements are listed in order of increasing atomic number, many of their properties go through cyclical changes, with elements of similar properties recurring at intervals.[1] For example, after arranging elements in their increasing atomic numbers, many of the physical and chemical properties of Lithium, such as its vigorous reactivity with water, recur in sodium, potassium and cesium.

This principle was discovered by Russian chemist Dmitri Mendeleev in 1871 after a number of investigations by scientists in the 19th century. Mendeleev also proposed a periodic system of elements that was based not only on atomic weights but also on the chemical and physical properties of the elements and their compounds.[2] In 1913, Henry Moseley determined that periodicity depends on the atomic number rather than atomic weight. Lothar Meyer presented his table several months after Mendeleev, but opposed his Periodic law. Initially, no theoretical explanation for the Periodic Law was available and it was used only as an empirical principle, but, with the development of quantum mechanics, it became possible to understand the theoretical basis for the Periodic Law.

The periodic recurrence of elements with similar physical and chemical properties, when the elements are listed in order of increasing atomic number, results directly from the periodic recurrence of similar electronic configurations in the outer shells of respective atoms.

The Discovery of Periodic Law constitutes one of the most important events in the history of chemical science. Almost every chemist makes extensive and continued use of Periodic Law. Periodic Law also led to the development of the periodic table, which is widely used nowadays.