question_answer 77)

  Ionisation enthalpies of elements of second period are given below : Ionisation enthalpy (kcal\[mo{{l}^{-1}}\]): 520, 899, 801, 1086, 1402, 1314, 1681, 2080 Match the correct enthalpy with the elements and complete the graph given in the following figure. Also symbols of elements with their atomic numbers.

Answer:

  The second period elements with their symbols, atomic numbers and ionisation enthalpies are given below :  

Symbol	Li	Be	B	C	N	O	F	Ne
At. Number	3	4	5	6	7	8	9	10
\[\Delta {{H}_{1}}(kJ\,mo{{l}^{-1}})\]	520	899	801	1086	1402	1314	1681	2080

  In a period, the value of ionisation enthalpy increases from left to right with breaks where the atoms have somewhat stable configurations. Be and N have higher values than expected. Be has fully filled orbital while N has half filled orbitals. Be: \[1{{s}^{2}},2{{s}^{2}}\] N : \[1{{s}^{2}},2{{s}^{2}},2p_{x}^{1},2p_{y}^{1}2p_{z}^{1}\] Complete the graph yourself and compare with the graph given in problem 38.