Tuesday, January 24, 2012

How do you ionicaly bond lithium and oxygen? what order will the shells go in?

how to you make the shells stable/complete? please help im stuck on my chemistry h/w!

How do you ionicaly bond lithium and oxygen? what order will the shells go in?
Li has electronic structure 1s^2 2s^1 so will lose an electron from its outer shell to become Li^+

O has electronic structure 1s^2 2s^2 2p^4 so needs to GAIN 2 electrons to fill its outer shell and become O2^-.It can gain one elctron from each Li, so you need 2 Li and 1 O to make Li2O
Reply:Let us begin our journey through this problem by considering the electron configurations of Lithium and Oxygen respectively



for lithium: 1s2 2s



for oxygen: 1s2 2s2 2p6



Now both lithium and oxygen must change their electronic configurations to achieve stability, that is to become isolectronic (have the same electron configuration) with the noble gas in the same period or the previous one. In order to facilitate this, oxygen can either gain two electrons in the formation of an ionic bond with a metallic element, or share four electrons (two from oxygen itself) with a non metallic element in the form of a covalent bond.



It will then become isoelecronic with neon, having the electron configuration:



1s2 2s2 2p6



Notice how the oxygen now has 8 electrons in its outer shell, which is the most stable form.

If two electrons are gained oxygen will now be a negatively charged anion with the formula [O]2-



Lithium will only lose its one valence electron to another electronegative element in the form of an ionic bond. It will then be isoelectronic with helium with the E.C



1s2



Lithium will then have a single positive charge, forming a cation with the formula [Li]+.



Notice how lithium now only has 2 electrons in its valence shell, which is the maximum the first shell can hold.



Now one can achieve the fomation of lithium oxide, the ionically bonded salt by heating lithium metal in air



word equation



lithium + oxygen ---%26gt; lithium oxide



symbol equation



4Li(s) + O2(g) ---%26gt; 2Li2O(s)



(notice how it takes two lithium atoms to bond with one oxygen, as that is the ratio between the charges on their ions)



ionic equation



2[Li]+ + [O]2- ---%26gt; 2[Li]+[O]2-


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