Question

explain the exception of the general trends



more than 300 words answer needed

Answer 1

Several of the Periodic Trends have exceptions and/or inconsistencies. To have really mastered periodic trends, you must also understand these exceptions.

Electronegativity

This is the easiest of the exceptions. We have said that electronegativity increases to the right. This is true except that the trend does NOT include the noble gases. That means that fluorine has the highest electronegativity, not Ne or He. This is because the definition of electronegativity contains the phrases "in a covalent bond." Since the noble gases don't bond, they don't have electronegativities.

It should be noted that a few of the noble gases have been forced to bond (at high temperture and high pressure with fluorine). You may find tables that, therefore, list values for the electronegativity of Xe and Kr, but these are not terribly important values to know.

Ionization Energy

If you were to graph Ionization Energy v. Atomic number for the elements in the second period (row) of the table, you would expect something that looks like this  { refer image 1}

Note that Boron has a lower Ionization energy than Beryllium and that oxygen's ionization energy is lower than nitrogen's

Answer 2

exceptions to the general trends
1) alkaline earth metals:

alkaline earth metals have completely filled s - subshell
therefore it is difficult to add an electron .the added electron should enter new subshell of higher energy
so this would be endothermic process


2) half filled orbitals :

electron gain enthalpies of elements having exactly half filled orbitals are essentially endothermic
eg: nitrogen family bl addition of an electron to relativity stable half filled no orbitals require energy


3) ns2 np6 :

noble gas elements with completely filled orbitals have relatively high stability.addition of an electron to a stable configuration requires energy that is electron gain enthalpy is endothermic


4) flourine and chlorine:

electron gain enthalpy of flourine is surprisingly less negative than chlorine because addition of an electron to small sized 2 s orbital of flourine is more difficult than that to relativity larger 3 p orbitals of chlorine


flourine (-328 kJ )
chlorine (-349kJ)




hope it may help u



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