[777888]

I have some questions about electronegativity, polar molecule, and Lewis structure!

Electronegativity:
For example, How can I know if BH3 and BF3 are ionic or molecular? When you determine if a compound is ionic or molecular, do you look at the electronegativity difference or use the rules:
metal+non-metal->ionic
2 non-metals->molecular



Polar molecule:
I don't get why H2O2 is a nonpolar molecule.



Lewis structures:
For H2CO, why the 2 H do not bond with O? Is H2CO an oxyacid? (As I know, in oxyacid, H would bond to O)


I am confused about these concepts for a long time!

Can someone help me? Thank you!

[Mitch]

2 nonmetals will not have an ionic bond, typically.

[Tetrahedrite]

H2O2 is non-polar because the dipole forces are symmetrical and as such cancel each other out. The dipoles in H2O point in towards the oxygen at around 109 degrees to each other and therefore do not cancel out.
As for H2CO (the compound formaldehyde I believe) the Hydrogens cannot bond to the oxygen because this would disobey the valence rules for both C and O. The O is double bonded to the C and the molecule is therefore not an oxyacid.

[777888]

Thanks a lot!

Also, is HNO3 an ionic compound?

[Tetrahedrite]

HNO3 (nitric acid) is an ionic compound and dissociates completely to H+ and NO3-

[jkrumh1]

2 nonmetals will not have an ionic bond, typically.

Are you sure about this?  Im pretty sure that it two nonmetals that bond are covalent.  

[777888]

HNO3 (nitric acid) is an ionic compound and dissociates completely to H+ and NO3-

Why when we draw Lewis structure for HNO3, H is bonded to 1 of the O, like the H-O bond is covalent?

[Mitch]

No molecule is either wholly ionic or completely covalent. It's really more of a gray. The term covalent comes from Molecular Orbital Theory. There isactually an ionic term in MO Theory entrenched in its equations. So even when you say the word covalent it implies that there is still some ionic part included,

[Demotivator]

Yeah, there are gray areas. However, If one is forced to make a determination between the two, I would say covalent. The "ultimate" determinator is whether the compound can exist as a molecule in some phase. NaCl can't (ionic). HNO3 (i think) can (covalent) as a gas.

[Donaldson Tan]

2 nonmetals will not have an ionic bond, typically.

iodine is known to exihibit metallic character

[Mitch]

"typically"