Ionic or Covalent?

[JohnDoeDDS]

Hi guys. I need some help please. This isnt really a DAT question (it might be) I am just doing chem I, and saw some poeple posted problems and I am having some real trouble with this. I have to answer these two questions by tomorrow morning and I just cant see how to do it.

I have to determine wether this commpound is Ionic or Covalent.

CuSO4

Cu(NO3)2

CaCO3

Could some1 not just gimme an answer but explain it a lil. I understand that if its gas-metal bond that its ionic, otherwise its covalent. But its these polyatomic ions that get me confused. Thanks a lot for your help!

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[hb2998]

Don't quote me on this.... But I remember the easiest way to figure out if a compound is Ionic or covalent is to take the difference of the electronegativity of the atoms. If the difference is more than 1.8 (i think..) then the relationship is Ionic.

EN here refers to difference in EN btw two atoms.
Covalent: EN < 1.2
Polar: 1.2 < EN < 1.8
Ionic: EN > 1.8

Example:
CaCO3

EN of Ca = 1.0
EN of O = 3.5

3.5-1.0 = 2.5..... CaCO3 is ionic... there are 3 Highly electronegative oxygens right next to that carbon.. making that carbon pretty positive. The oxygens all share a -2 charge.. This charge attracts and keeps the Ca (which is actually +2).

This rule works a lot more clearly when you're dealing with just two atoms.. But when dealing with compounds like the one in your question, just consider the most electronegative. Think of it logically. You have a cation (+ve charge).. where would it want to hang out?.. around the most electronegative atom (because electronegative atoms have most electron density).

CuSO4 is also ionic. CuNO3 also Ionic.

(If you're unsure.. theres always google.. Anybody please correct me if i'm wrong about anything. I would really appreciate it!)

 

[JohnDoeDDS]

awesome! Thanks man. Its weird because this question is asked in lab but we havent learned electronegativity in class. And I tried to look it up in the text and its very vague. Thanks for your help guys.

 

[drat]

OP, first know how to organize the periodic table into metals, metalloids (semimetals), and nonmetals, or know which atoms are the most and least electronegative. From there, a good rule of thumb to go by is if a metal (Cu, in this case) is with a nonmetal (SO4, for example), the bond is typically ionic because metals like to lose electrons (lower ionization energy) and nonmetals like tend to gain electrons (high negative electron affinity). Electrons are transferred in an ionic bond, whereas they are shared in a covalent bond. For a compound that is composed of just nonmetals, CO2 for example, the bonds are usually covalent.

Just to clarify, the electrons are not necessarily shared equally in covalent bonds. A covalent bond can be polarized, as it would be for NH3 or HF, or can be nonpolar, as in the case of O2 or CH4.

Eek...I fear I might confuse you more, so I'll stop. That's the best general overview I can give on the topic. Hope that helps.

 

[drat]

Don't quote me on this.... But I remember the easiest way to figure out if a compound is Ionic or covalent is to take the difference of the electronegativity of the atoms. If the difference is more than 1.8 (i think..) then the relationship is Ionic.

I believe the difference is 2.0. I know that HF is a polar covalent bond and I looked up the electronegativity values and the difference is 1.9. I did a google search and found a website that said 2, but the best reference would be a general chem book, which I unfortunately don't have. I think you did a good job answering the OP's question. I gave a "less scientific" answer in case EN tables aren't available.

 

[JohnDoeDDS]

I see, thanks drat. I think thats the way the professor explained it. Hes ******ed though and doesnt explain much to us. And the book seems very vague on this subject surprisingly. I was confused because I knew since SO4 is composed of all gasses than it had to be a covalent bond, but then Cu is a metal so I wasnt sure how a covalent bond and an ionic bond would work out... But now I see you just have to consider them seperately. We didn't learn about polar and non-polar yet so I wont ask you guys about it yet... But damn Im going ot be taking Chem II in the summer and its going to be one hell of a semester! Thanks guys for your help. I love this board!

 

[drat]

I see, thanks drat. I think thats the way the professor explained it. Hes ******ed though and doesnt explain much to us. And the book seems very vague on this subject surprisingly. I was confused because I knew since SO4 is composed of all gasses than it had to be a covalent bond, but then Cu is a metal so I wasnt sure how a covalent bond and an ionic bond would work out... But now I see you just have to consider them seperately. We didn't learn about polar and non-polar yet so I wont ask you guys about it yet... But damn Im going ot be taking Chem II in the summer and its going to be one hell of a semester! Thanks guys for your help. I love this board!

Yeah, you're right, the SO4 is composed of covalent bonds, but the species CuSO4 is ionic. 😉 Oh chemisty. Looks like you're "getting it," keep it up. 👍

 

[hb2998]

Good answer drat. Thanks for clarifying 😉 . (I was sure there was a different, more g-chem method of going about it). JD, hang in there buddy. G-Chem sucks, its a known fact. One you get to O'chem and you can draw lewis structures of these compounds, it will make it easy to see that the metals really don't have anywhere to "attach." Seriously, G-Chem is just a blur for me. I pulled off As, but I don't remember learning anything.... I haven't started reviewing, so I don't even know what was covered in that class. But I can tell you that there is light at the end of the tunnel (O'Chem). Life is pretty wonderful in O'Chem (although the class average one tests in my school does linger around 40%!!! ).. It really teaches you the essense of the molecules, making it easy to think about situations, rather than memorize routines. 🙂 Good luck.