Science : Ch 05 – Periodic of Classification of Elements

Atomic number X- 12 ,Y-17 Number of protons X-12, Y-17 Number of electrons X-12,Y- 17 Electronic configuration 2, 8, 2 2, 8, 7 Valence electrons X-2,Y- 7 Valency X- 2,Y- 1

The element with electronic confguration 2, 8 has octet confguration, so it must be an inert gas, i.e., neon, which is placed in group 18.

The elements of the 2nd period contain two shells: K and L shell. So, the outermost shell is L.

As we move from left to right in periodic table, metallic character decreases and non-metallic character increases. Here Na, Si, Cl, Mg, Al belong to same period.

Na and Mg belong to the sameperiod, whereas Na and K are in the same group.In a group from top to bottom, the atomic radius increases, whereas it decreases in a period from left to right. Hence, the order would be K ɳ Na ɳ Mg and K ɳ Ca ɳ Mg

Element  Y  has 1 less electron to complete its octet which is a property of nonmetals. On the other hand, element  Z  has 2 extra electrons to become stable which is a property of metals.

Non-metals form acidic oxides. The element with atomic number Ǫ is a nonmetal (nitrogen). Rest three elements with atomic numbers.

Eka-aluminum (later identified as gallium) has a valency of 3. Hence, the oxide would be of the molecular formula E₂O₃. Other options have a different valency of E.

As we move down in a group, the metallic nature of elements increases.  Be, Mg and Ca are present in the same group (group 2 of the modern periodic table).