How many electrons O- could share with cation?

[amanda.castro]

Hey, guys!

Considering the molecule XO- where X is an atom that makes single bond with oxygen. How many electrons he can "borrow" or "share" to the cations Na2+ or Mg2+?

I'm asking this because i thought he could "borrow" or "share" all his outermost electrons, in other words, eight. So, if a cation 2+ needs two electrons, he(O-) could do what i said, but i see some molecules like Mg(OH)2 and Na(OH)2 and this makes me confuse!

Thank you!

[Iota]

If X is an atom which makes a single bond with O, then 2 of Oxygen's electrons are made unavailable, because a single bond is the sharing of two electrons.

 

This means there are now 3 lone pairs of electrons around the Oxygen atom non-bonded (6 electrons available for bonding).

 

Note: the negative charge on XO-. This is because Oxygen likes to make 2 bonds to be stable by sharing 4 of its electrons (2 of its lone pairs, each bond = 2 electrons "shared").

 

Mg and Na will bond ionically (through electrostatic attraction) with XO-, to balance the negative charge. Na+ and Mg2+.

 

NaXO can be made or Mg(XO)₂. Because XO- has a negative charge of -1, it can bond to Na +1 stably in a 1:1 ratio.

 

Mg however has a charge of 2+ (+2 charge), and so TWO XO- (-1 charge x2 = -2 charge) molecules are required to bond stably. Hence, Mg(XO)₂.

 

 

 

(I can guess at some gaps in your understanding of how electron valency and the different types of bonding work; look into the periodic table and how it's set out, and research the different types of bonding.)

Edited July 3, 2014 by Iota

[amanda.castro]

 

Mg however has a charge of 2+ (+2 charge), and so TWO XO- (-1 charge x2 = -2 charge) molecules are required to bond stably. Hence, Mg(XO)2.

 

First of all, thank you for your answer!

 

I have more two questions related with this subject.

1- Well, if in my example oxygen XO- has 6 electrons available for bonding, why he cannot "borrow" 2 of them for Mg2+? Why is needed 2(OH)- to "satisfy" Mg2+?

 

2- The same thing happens with Na2+ and the others 2+ cations?

[amanda.castro]

Sorry bump this topic but i need an answer for my last reply above.

[Enthalpy]

No six electrons available at an oxygen atom, because six electron pairs (the others coming from the bonded atoms) would not fit on favourable orbitals.

 

For simple atoms like oxygen, molecular orbitals explain the simple idea of valence, where oxygen has the valence 2.

One example is given there, I suppose simpler and more general explanations exist elsewhere:

http://en.wikipedia.org/wiki/Triplet_oxygen

 

You could also play some time with the idea that reactions use to occur between already formed molecules like O₂, not between isolated atoms like O. This has many important consequences, useful to grasp.