In the modern periodic table, properties of the elements are a periodic function of their atomic numbers.
True/False

Answer

A

Explanation

There are numerous physical properties of elements such as melting points, boiling points, heats of fusion and vaporisation, energy of atomisation, etc, which show periodic variations.
The case of periodicity in properties is the repetition of similar outer electronic configuration after certain regualr intervals. e.g., all the elements of 1st group (alkali metals) have similar outer electronic configuration. i.e., `ns^(1)`.
`._(3)Li = 1s^(2).2s^(1)`
`._(11)Na=1s^(2), 2s^(1), 2p^(6), 3s^(1)`
`._(19)K=1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(6), 4s^(1)`
`._(37)Rb=1s^(2), 2s^(2), 2p^(6), 3s^(6), 3d^(10), 4s^(2), 4p^(6), 5s^(1)`
`._(56)Cs=1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(6), 3d^(1), 4s^(2), 4p^(6), 4d^(10), 5s^(2), 5p^(6), 6s^(1)`
`._(87)Fr=1s^(2),2s^(2),2p^(6),3s^(2),3p^(6),3d^(10),4s^(2),4p^(6),4d^(10),4f^(14)`
`5s^(2), 5p^(6), 5d^(10)6s^(2), 6p^(6), 7s^(1)`
Therefore, due to similar outermost shell electronic configuration all alkali metals have similar properties. e.g., sodium and potassium both are soft and reactive metals. They all form unpositive ion by the lose of one electron.
Similarly, all the elements of 17th group (halogens) have similar outermost shell electronic configuration, i.e., `ns^(2)np^(5)` and thus possess similar properties.
`._(9)F=1s^(2) , 2s^(2), 2p^(5)`
`._(17)Cl=1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(5)`
`._(35)Br=1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(6), 3d^(10), 4s^(2), 4p^(6), 4d^(10), 5s^(2), 5p^(5)`
`._(53)I= 1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(6), 3d^(10), 4s^(2), 4p^(6), 4d^(10), 5s^(2), 5p^(5)`
`._(85)At=1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(6), 3d^(10), 4s^(2), 4p^(6), 4d^(10), 4f^(14), 5s^(2), 5p^(6), 5d^(10), 6s^(2), 6p^(5)`