Which one has the most covalent character?

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Sinay
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#1
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How would you work out:

Which one of the following has the most covalent character?
A MgF2
B MgBr2
C AlF3
D AlBr3

It's on the synoptic paper in chemistry, but i don't know how i would do it in the exam without knowing the electronegativities of the elements.
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bekahchu
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Look at where they are in the Periodic table, the ones nearest each other, group-wise, are the most covalent.
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modini
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You know that electronegativity increases from left to right and from down to up...

I would say it was MgBr2
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xinolisss
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Magnesium Fluoride is ionic as well as Magnesium Bromide, so those two are out,

AlF3 and AlBr3, well Fluorine has the greater electronegativity hence I would guess D then? right?

In general Electronegativities decrease down the group and increase across (left to right) a period...
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quintsy
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Moved to Chemistry.
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xinolisss
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(Original post by modini)
All of the molecules are ionic...
Are you sure?
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modini
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Sorry come to think of it they're not :p:
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pengu
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I think AlBr3
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xinolisss
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(Original post by modini)
Sorry come to think of it they're not :p:
Now that's better...
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Creative
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AlBr3

Al3+ is more polarising than Mg2+ and the Br- (higher charge + smaller ionic radius), the anion is large and polarisable.
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Punk Phloyd
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AlBr3

You want the one with lowest difference in electronegativies.
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Sinay
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(Original post by xinolisss)
Try to work it out mate, it ain't that difficult

Magnesium Fluoride is ionic as well as Magnesium Bromide, so those two are out,

AlF3 and AlBr3, well Fluorine has the greater electronegativity hence I would guess C then? right?

In general Electronegativities decrease down the group and increase across (left to right) a period...
yeah when i was doing the practice test i put C, but the answer is D.
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modini
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AlBr3

You want the one with lowest difference in electronegativies.
Ditto ^
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georgeElsworth
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It is AlBr3...I dont think you need electronegativities, just FAJAN'S RULES..

Al^3+ is a smaller molecule and has higher positive charge then Mg^2+
Br- is a bigger molecule then F-

Therefore more covalent as the electron cloud of Br is attracted more and its more negative...
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Sinay
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yeah i get it now - thanks
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ArinSom
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This question can be solved by Fajan's Rule. According to the rule, smaller size of cation and larger size of anion favours more of covalent character. The opposite will result in more of ionic character
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EierVonSatan
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#17
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#17
(Original post by ArinSom)
This question can be solved by Fajan's Rule. According to the rule, smaller size of cation and larger size of anion favours more of covalent character. The opposite will result in more of ionic character
Please look carefully at the dates of threads before posting, this thread is nearly 10 years old.
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