Chemistry....?

Question

What are all of the thought processes one engages in when determining the polarity of a covalently-bonded molecule?


i need help with some chemistry homework, well, its make up work, and i have only tonight to finish, final grades are due tommorow...so if you can plz help me.

Answer 1

Start with electronegativity of all the bonded atoms on to the central atom(s). Electronegativity generally increases as you go to the right in a row and up in a period (column). Use a list of Paulings scale of electronegativities if in doubt. For the 2nd row of elements: Li, Be, B, C, N, O, F: the electronegativities are 1, 1.5, 2, 2.5, 3, 3.5, 4.

Compare the electronegativities and if there is a difference in electronegativities, the molecule is a good candidate.

Next determine the actual shape of the molecule. You can use VESPR to find the shape.

Determine if the molecule has any symmetry elements in it. ie- is there an internal plane of symmetry? If symmetry found, inspite of individual dipoles, the molecule will have a net zero dipole. This feature can be quite challenging. Knowing the hybridization of the central atom is very helpful. For example CH3Cl has a dipole (sp3 and C-Cl bond is polar, no symmetry). CH2F2 has no dipole (sp3, inspite of individual C-F dipoles because symmetric). Trans ClCH==ClCH is not polar and the cis isomer is polar, again due to symmetry in the cis isomer.

Answer 2

First figure out which atom are bonded together (Lewis dot structures are good for this).

Look at the two atoms on either end of a bond; find out if their electronegativities differ (usually if they are different atoms their electronegativities are different). If they are different then one atom "pulls" on the electrons in the bond more strongly than the other atom. This makes the stronger atom slightly negative and the weaker atom slightly positive. That makes a polar bond.

Look at the shape of the molecule. Do the bonds cancel each other? (Think of it as a tug of war) Usually symmetrical molecules have bonds that cancel. If the bond "pulls" cancel then the entire molecule will no nonpolar.

Answer 3

It has everything to do with the electronegativities of the atoms in question bonded to each other. Visit the site below and read the section on "Polar Covalent Bonds" about 1/2 way down the page.


http://www.chem.ufl.edu/~chm2040/Notes/Chapter_11/covalent.html

Answer 4

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Answer 5

Is one or both atom Known as electropositve or electronegative

Example Hydrogen is a strongly electropositive element. chlorine is strongly electronegative one.

So ,the molecule HCl is polar since the Chlorine atom will present a negative pole and the hydrogen a positive pole

hoping this helps

Answer 6

huh?