Which of the following molecules have net dipole moments? For the molecules that are polar, indi

Which of the following molecules have net dipole moments?...

Key Concepts

Molecular Geometry

Molecular geometry refers to the three?dimensional arrangement of atoms in a molecule. This arrangement is critical because it affects how individual bond dipoles (vectors representing the difference in electronegativity between bonded atoms) combine. If the geometry is symmetrical, the bond dipoles may cancel out, leading to no net dipole moment, whereas an asymmetrical distribution results in a net dipole moment.

Electronegativity

Electronegativity is the measure of an atom's ability to attract shared electrons in a bond. Differences in electronegativity between atoms create polar bonds with partial positive and negative charges. The magnitude and direction of these bond dipoles are determined by the differences in electronegativity, influencing the overall polarity of the molecule.

Bond Dipole

A bond dipole is a vector quantity that represents the separation of electrical charge within a chemical bond due to the difference in electronegativity of the two atoms. Its magnitude depends on the charge difference, and its direction is from the less electronegative atom toward the more electronegative atom. Bond dipoles are the building blocks that, when added vectorially, determine the net dipole moment of a molecule.

Symmetry and Dipole Cancellation

Symmetry involves the spatial arrangement of bonds in a molecule. In molecules with high symmetry, individual bond dipoles may cancel each other out, leading to a nonpolar molecule. Conversely, in molecules with lower symmetry or with substituents that disturb the symmetrical arrangement, the bond dipoles do not fully cancel, resulting in a net dipole moment.

Polarity of Molecules

Molecular polarity is a measure of the separation of positive and negative charges within a molecule. It arises when there is an uneven distribution of electron density due to differences in electronegativity and an asymmetrical molecular geometry. The overall polarity is determined by the vector sum of all bond dipoles, which can either cancel out in nonpolar molecules or add up to produce a net dipole moment in polar molecules.

Transcript

00:01 So in this video, we're going to go over question 144 from chapter 8, which says which of the following molecules have net dipole moments.

00:08 For the molecules that are polar, indicate the polarity of each bond and the direction of the net dipult moment of the molecule.

00:15 So in a, we're given ch2, cl2, chcl3, and ccl4.

00:21 So in ch2, our carbon atom is going to bring four valence electrons.

00:27 Each of our hydrogen atoms brings one, and our chlorine atoms each brings seven.

00:31 So that's a total of 20 electrons to draw our lewish structure with.

00:36 So we draw our two chlorine atoms bonded to our central carbon atom and then our two hydrogens.

00:45 And then we can fill in the octet on our chlorine atoms and that uses of 16, 18, 20, that uses up all 20 of our electrons.

00:59 And the formal charge on each atom in this lewish structure is zero for carbon, it's 4 minus four and for chlorine it's seven minus six minus one so it's zero on for all atoms then for c h cl three our carbon atom brings four valence electrons hydrogen brings one and the three corines each brings seven so we have a total of 26 so we have our three chlorine atoms bonded to our central carbon atom and our one hydrogen atom then we can fill in our octets and that uses up eight times three plus two electrons so that uses up all 26 of of our electrons.

01:42 So we essentially have the same structure, but with one of our hydrogen atoms replaced with the chlorine atom.

01:49 Then in ccl4, carbon brings four valence electrons.

01:52 Each chlorine atom brings seven.

01:53 We have a total of 32.

02:00 We fill in the octet on all four chlorine atoms, and that's going to use up eight times four of our electrons.

02:07 That's 32 electrons, that's all of them.

02:12 So we have our lewish structures.

02:14 So in each of these, we have one atom, surrounded by four atoms and zero lone per electrons.

02:20 So that means we have a tetrahedral geometry.

02:23 So what does that tell us about the polarity? well, in the case of ch2, cl2, we have two polar bonds from our carbon to our chlorine.

02:32 Chlorine is more electronegative than carbon.

02:35 So we end up with a partial negative on our chlorine atoms and a partial positive on our carbon atom.

02:43 And our net dipole moment is pointing in this direction towards our chlorine atoms.

02:49 So this is polar.

02:51 Then we have chcl3, and again, each of our carbon chlorine bonds is polar.

02:58 So we have three partial negatives on our chlorine atoms, and then a partial positive on our carbon atom.

03:06 And the net dipole moment is in the direction of our three chlorine atoms in that direction.

03:14 So that molecule is also polar.

03:17 Then we have ccl4.

03:19 Again, our carbon -chlorine bonds are all polar bonds, but in this case, they're placed symmetrically in our tetrahedral geometry, since we have four of them.

03:31 They're placed symmetrically, and so the overall dipole moment, there is no overall dipole moment, and this is a non -polar molecule.

03:40 So in ccl4, even though we have the same c -cl -4, c .l bonds that we had in ch2cl and chcl3, the symmetric placement of the carbon chlorine bonds makes us a non -polar molecule.

03:55 In b, we're given co2 and n2o.

04:00 So our carbon atom is going to bring four valence electrons, and then each of our oxygen atoms brings six valence electrons, so we have a total of 16 electrons to draw our lewish structure with.

04:10 So our central atom is going to be the least electronegative atom, so that's our carbon atom.

04:17 And then we can draw that bonded to both of our oxygen atoms.

04:20 If we were to just fill in the octet on our oxygen atoms, that would give us a formal charge of minus one on each of our oxygen atoms, 6 minus 6 minus 1 and plus 2 on our central carbon atoms.

04:35 So let's not do that.

04:38 It'll be better if we draw double bonds to the carbon atom.

04:44 So that way our carbon is making four bonds.

04:47 So the formal charge will be 4 minus 4.

04:50 It'll be 0...

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