[SoleSky]

Hello,
I am new to this forum so I understand if my question is not answered straight away. However, I have a test coming up on Friday so I had a few questions about my chapter on chemical bonding. 

To be more specific, can somebody explain to me the difference between polar and nonpolar.  I know polar is unequal sharing of electrons, but what does that mean? 

Also, problems such as NaCl Cl-3.16 (electronegativity) subtracted by Na- .93 (electronegativity) which results in 2.23. This, according to my teacher, is Ionic, which has a difference of 1.7 or greater.  So what is the difference between Ionic and Polar? 

I was also wondering if someone could explain what metallic bonding is, and possibly give me an example. My teacher said that it was a bond between Cu'.  If you could answer my questions, or need me to reword that would be great.

[stewie griffin]

I think you are using "metallic bonds" to mean ionic. Metallic bonding is actually different from ionic, so if I my assumption of what you mean is incorrect please let me know and I will try to help.
In chemistry there are different types of chemical bonds. The two you are discussing are ionic and covalent. Ionic means that one atom in the molecule is completely giving up one or more of it's electron(s) to a different atom in the molecule. So in NaCl the sodium atom gave up its one valence electron (those are the electrons that participate in bonding) to chlorine. Since sodium lost an electron it becomes positive, chlorine gained an electron so it's negative. You should know that positive charges and negative charges attract one another. Thus after sodium gives up its electron, the Na⁺ and Cl^- are attracted to each other.
Covalent bonding is when two atoms decide to share one or more electrons. In Cl₂, each chlorine atom contributes one electron to the chemical bond. Thus the bond is made up of two electrons. Even though each chlorine brought in one electron, that electron pair is now shared between the two atoms. The bond then results from a sharing of electrons rather than attraction of opposite charges.
The problem is that there's a spectrum of bonding. Red and orange are separate colors, yet there's a spectrum of colors that exist as we go from red to orange. Similarly, ionic and covalent are separate types of bonds but there's some bonds that have ionic character and covalent character. This is where the issue of polar/nonpolar comes in and the idea of electronegativity.
If it's an ionic bond, it's polar. If it's a covalent bond between two atoms of the same electronegativity (such as in Cl₂ both atoms get to share the electrons equally, thus it is nonpolar. Yet if we look at H₂O, we see covalent bonds. However the oxygen is far more electronegative than hydrogen, so even though H and O are sharing electrons, the O "hogs" more than it's fair share. This causes the oxygen to bear "more electron density" than the H does. So oxygen is partially negative (since it's hoarding the electron pair) and the hydrogens are partially positive (since they aren't getting their fair share of the electrons). This results in a polar molecule.
Read that over and compare to your class notes...see if it starts to make more sense. Then, with a better understanding come back and ask about anything that's still not clear.
Hope this helps.

[SoleSky]

Yes, I knew the difference between covalent and Ionic. After some research I came to the conclusion that metallic bonds were bonds consisting of the same element. However, when you said that Ionic bonds are polar and covalent are nonpolar, that helped. I am having a little trouble understanding the background of it all. As for water, is that an exception to the rule? Or am I just not understanding it correctly? Also do you know how to explain a lattice structure? Thanks so much for your help.

[stewie griffin]

When you say "is water an exception", could you clarify what it's an exception to? I don't know if I understand your question.
The lattice structure is the overall structure of a solid ionic compound. Since a positive Na can be attracted to any negative Cl, the atoms pack together like spheres in the solid state. In NaCl each Na⁺ is surrounded by six Cl^-'s, and each Cl^- is surrounded by six Na⁺'s. However, it is still convenient to think of the chemical bond as existing between just one sodium atom and one chlorine atom. Once you put solid NaCl into water, the lattice breaks up and we have solvated Na⁺ ions and Cl^- ions.
Note, not all convalent bonds are nonpolar. That's what I meant when I said there's a spectrum of bonds between pure covalent and pure ionic. Water is not an exception in this sense. It is a covalent bond b/c the O and H are sharing electrons. However, since O is more electronegative, these electrons are ^not shared equally. Polar covalent bonds will result anytime there is unequal sharing of electrons (thus the greater the difference in electronegativity between the atoms involved in bonding, the more polar the bond). However, in water the electrons are still shared (even though it's unequal), and thus it's a covalent bond. Once the electronegativity difference becomes so great (as in the case of Na and Cl) the sharing of electrons is essentially nill and it is convenient to view the bond as ionic. This is why your teaching is trying to give you some rules of thumb by saying anything will an electronegativity difference greater than 1.7 should be considered ionic.
To sum up... covalent bonds can be polar or nonpolar. You have to look at the electronegativities. A rule of thumb though is that whenever you have a covalent bond between two different atoms, there is bound to be an electronegativity difference and thus the bond will be polar (even if it just slightly).

[stewie griffin]

Let me give you a simpler rule of thumb for ionic bond vs. covalent  . By now you should be able to tell what is a metal and what is a nonmetal (just by looking at the periodic table). For highschool chemistry, we can say that anytime there is a bond between a metal and a nonmetal that it is an ionic bond. Anytime there is a bond between a nonmetal and nonmetal, it is a covalent bond (though it can be nonpolar or polar!).
This is of course somewhat of a lie  . The transition metals (aka the "d block") don't actually bond with nonmetals in a purely ionic or purely covalent fashion and thus molecular orbital theory is invoked to explain the bonding. However, this is beyond the scope of a highschool chemistry class. Thus the above rule will work just fine for your purposes.

[SoleSky]

Yes, thank you very much, I understand what you mean.  I am in more of an honors chemistry class, so we go through these topics rather quickly.  I understand most of it, my problem is trying to understand information that is thrown infront of me without any background knowledge of the source. I do now understand polar and nonpolar. Thank you for answering my question. In that topic, are all diatomic molecules nonpolar then, because their electronegativities cancel eachother out?

[stewie griffin]

Yes, all the diatomic molecules (H2, N2, O2, F2, Cl2, Br2, I2) are nonpolar since as you say the electronegativities cancel out.

[SoleSky]

Okay, thank you very much, very helpful.