Easy Question...TBR Orgo Ch.1

[FutureDoc2]

Hey Guys,

Im looking for some clarification about polar-covalent molecules. I know covalent is the sharing of electrons and ionic is practically based on electronegativity, however when is a molecule consider polar-covalent/non-polar covalent? I know in TBR it says if its partially covalent and partially ionic, but how would I be able to distinguish that from the rest? I think I may just be over looking something...Thanks in advance!

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[Pisiform]

Hey Guys,

Im looking for some clarification about polar-covalent molecules. I know covalent is the sharing of electrons and ionic is practically based on electronegativity, however when is a molecule consider polar-covalent/non-polar covalent? I know in TBR it says if its partially covalent and partially ionic, but how would I be able to distinguish that from the rest? I think I may just be over looking something...Thanks in advance!

Covalent Bond is the sharing of electrons and takes place in non-metals. Ionic bond is transfer of electrons and takes place between metal and non-metal.

In a bond, if the electronegativity difference is greater than 2.0 then it is ionic. If the electronegativity difference is less than 1.5 then it is covalent. If the electronegativity difference is between 1.5 and 2.0 then it is polar covalent.

But the point is you wont remember the EN values of each element do you. So main idea is that if one element in a bond is very electropositive (usually metals) and other is electronegative (non-metal) it is ionic bonding. If one is mildly Electronegative and the other is very electronegative e.g. you can look at the EN (F,O,Cl,N,Br,S,C,H) - H is mildly EN while Cl is very EN then it would form polar-covalent bonds. You have to be careful for example if the molecule is symmetrical or not. Symmetry cancels out dipole and make molecule non-polar. Like in CCl4 individual molecules are polar but overall the molecules is non-polar because it is symmetrical.

If the electronegativity of two elements in a bond is close to each other, which happens in when we have the same two elements e.g. Cl2 = Cl -Cl bond is nonpolar

 

[Erythropoietin]

In order to gain the stability of a noble gas configuration, some atoms can transfer electrons to each other; this is ionic bonding (NaCl, CaCl2, etc.) So the metals in the examples transferred their electrons to their nonmetals (Na to Cl , Ca to Cl).

Sometimes atoms do not want to give up their electrons. They end up sharing their electrons with other atoms and form a covalent bond. The sharing of electrons can be equally or unequally.

In a nonpolar covalent bond, the two atoms involved share their electrons equally (example of this include all the diatomic elements: Fl2, Cl2, Br2, I2, N2, H2, O2)

In polar covalent bonds, electrons are shared unequally (example: HCl, water, peptide bonds, amines). For example, the covalent bond in HCl is polar because the two atoms have a moderate difference in electronegativity. Cl gains a partial negative charge, and the H gains a partial positive charge. A molecule that has such a separation of positive and negative charges is called a polar molecule. Note that this is not an ion because there is no excess of proton or electrons, but simply a charge separation in the neutral molecule.

So, to sum it up...if an electron pair is 50/50 shared between two atoms, then the bond is a nonpolar covalent. If the electron pair moves a bit towards the more electronegative atom of the pair, it becomes a polar covalent bond. If the pair moves completely to one end the bond is called an ionic bond.