Periodic Classification of Elements Test - 8

Electronic configuration of Al is 2,8,3

To form Al³⁺ , electronic configuration of Al is 2,8.

Electronic configuration of Mg is 2,8,2

To complete its octet, it will lose two electrons readily and form divalent ion, Mg²⁺.

Instead of limitation, it is one of the greatest merits of Mendeleev's periodic table. He had already predicted the existence of some elements that had not been discovered at that time. When these elements were discovered later on, they were placed in those gaps, withuot disturbing the existing elements.

The first element of the lanthanide series is called lanthanum with atomic number 57.

Statement A : Fluorine, though higher than chlorine in the periodic table, has a very small atomic size. This makes the fluoride anion so formed unstable (highly reactive).As a result, fluorine has an electron affinity less than that of chlorine.

Statement B: Carbon monoxide is a neutral oxide

Statement A: Sometimes, energy is to be supplied to the atom while adding electron to it.

Statement B : Since, both Tellerium and Polonium shows properties of both metals and non-metals, therefore, they are semi-metals.

The element in the last of the 3rd period is a noble gas i.e. its octet is complete. So, it has 8 valence electrons in its outermost shell.

On moving from left to right in a period, the atomic size decreases. So, lithium(Li) being on the extreme left has the highest atomic size and oxygen(O) being on the extreme right side of period 2 has the least size. 

As we go down in a group, one more electron shell is added at each stage and size of the atom increases. The valence electrons become more and more far away from the nucleus and so the atom can lose electrons more easily to form positive ions. Therefore, metallic character increases down the group.