Question

Please give notes on modern periodic table,groups,periods and position of elements

Answer 1

MORDERN PERIODIC TABLE Mendeleev’s periodic table was based on atomic weight. In 1913, Moseley from his studies on X-rays found that the atomic number is the more fundamental property of an element than its atomic mass. Thus, atomic number was adopted as the basis of modern periodic table. Moseley’s periodic law was then formulated as: The properties of an element are a periodic function of its atomic The periodic table based on this law is known as the modern periodic table. This periodic table is also known as Long or Extended Form of the periodic table. In the Mendeleev’s periodic table the subgroups A and B have been kept together giving rise to short periods. In the modern periodic table, the subgroups A and B have been separated so that the periods have been extended. Therefore, the older version of the periodic table is also called the short form of periodic table and the modern periodic table is called the long or extended form of the periodic table. A period in the periodic table is one of the horizontal rows, all of those elements have the same number of electron shells. Going across a period, each element has one more proton and is less metallic than its predecessor. Arranged this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic law. For example, the alkali metals lie in the first column (group 1) and share similar properties, such as high reactivity and the tendency to lose one electron to arrive at a noble-gas electronic configuration. As of 2016 a total of 118 elements have been discovered and confirmed The columns are called groups.A group or family is a vertical column. in the periodic table. Groups usually have more significant periodic trends than periods and blocks, explained below. Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell. Consequently, elements in the same group tend to have a shared chemistry and exhibit a clear trend in properties with increasing atomic number. However, in some parts of the periodic table, such as the d-block and the f-block, horizontal similarities can be as important as, or more pronounced than, vertical similarities The position of an element in the Periodic table tells us about its chemical reactivity. The position of an element in the periodic table is generally determined by its electronic configuration e.g. electronic configuration of sodium is 2, 8, 1 i.e., it has three shells and one electron in the outermost shell. Hence, it is placed in period number 3 and group number 1. However, in the case of transition elements this pattern is not followed.