How would you determine if the overall molecule is polar or nonpolar?

Answer 1

Polar Bonds and Molecular Shape

A polar molecule is a molecule that has a net dipole moment due to its having unsymmetrical polar bonds. There are two factors that go into determining if a molecule is polar or not. To determine if a molecule (or ion) is polar or non-polar, you must determine both factors.

• The polarity of the individual bonds in the molecule.
• The shape or geometry of the molecule.

First, to determine if a given individual bond is polar, you need to know the electronegativity of the two atoms involved in that bond. To find the electronegativities of all the elements, look at the Periodic Table (follow the link below this answer under Web Links).

If the electronegativity of the two atoms has a difference of 0.3 or less, then the bond is non-polar. If the electronegativity difference is greater that 0.3 but less than 1.7, then the bond is polar. If the two values have a difference greater than 1.7, then the bond is ionic, which is just very very polar.

Once you know which bonds in the molecule are polar and which are non-polar, you must use the shape of the molecule. You need the shape because two polar bonds, if oriented correctly can cancel each other out (like two equally strong people pulling in opposite directions on a rope -- nobody moves).

The three possible outcomes:

• If all bonds are non-polar, then the whole molecule is non-polar regardless of its shape.
• If there is symmetry in the molecule so that the polarity of the bonds cancels out, then the molecule is non-polar. A common example of this is carbon dioxide, or CO2. The molecule is linear, and its Lewis dot structure is like this: O=C=O (this doesn't include two sets of lone pairs on each oxygen). The carbon-oxygen bond is a polar bond, but because they are exactly opposed to each other, the molecule is overall non-polar. Another example of this is CCl4, where each carbon-chlorine bond is polar, but the molecule is non-polar. Here, how they cancel out isn't as obvious, but they do. CCl4 is a tetrahedral molecule, and the 4 C-Cl polar bonds cancel each other out.
• If there are polar bonds but there is no symmetry such that they cancel each other out, the overall molecule is polar. Water is a typical example of this. The two O-H bonds are oriented in a V-shape, and so the don't cancel out. Similarly, CH3Cl is also polar. It is the same shape as CCl4 (see above), but now it doesn't have the same symmetry because there is only one C-Cl bond and the bonds don't cancel out anymore.

Answer 2

Asker As the first answerer said, polar and non-polar are terms that apply only to molecular compounds (compounds that are joined only by covalent bonds). The atoms in the permanganate ion are held together covalently, but the bond between the potassium ion and the permanganate ion is, well, ionic.

There are convenient lists of solubility rules that allow you to memorize a few key statements rather than learning each ionic compound's solubility on a case-by-case basis. You can find a good list here:

http://www.csudh.edu/oliver/chemdata/sol...

Since KMnO4 contains a group I cation (K+), it IS soluble in water.

Now, as for your main question (how do you know if a compound is polar or non-polar)...you have to know something about molecular geometry.

I'm going to assume that you know how to draw Lewis structures and determine a molecule's geometry based on the assumptions made by VSEPR theory. If you don't, this next part isn't going to make a lot of sense. While most molecules are made of polar bonds (diatomic molecules like H2 and N2 being obvious exceptions), not all molecules are polar. It depends on how those polar bonds are oriented in three-dimensional space. If the bonds are arranged in such a way that electrons are more strongly pulled toward one side of the molecule and away from the other side, the molecule as a whole will be polar.

If the molecule is arranged in such a way that the electrons are very evenly distributed, then the molecule will be non-polar. If you can draw a molecule's Lewis diagram, it's pretty simple to figure out whether it is or isn't polar:

For molecules that have a single central atom (like H2O, CH4, NH3, etc).

If the central atom has one or more lone pairs of electrons, the molecule is most likely polar. End of story.

If the central atom has no lone pairs and all of the outer atoms are identical, the molecule is most likely non-polar.

If the central atom has no lone pairs and the outer atoms are NOT identical, the molecule is most likely polar.

For example, you can predict a water molecule's polarity because the central oxygen atom has two lone pairs of electrons on it. CH4 has no lone pairs on its central carbon atom, and all of its outer atoms are identical (H), so it's definitely non-polar; CH3Cl has no lone pairs on its central carbon atom, but one of the hydrogen atoms has been replaced by a chlorine atom. Since the chlorine atom is going to draw electron density toward its side of the molecule, CH3Cl is polar.

For organic molecules, which often have more than one central atom, determining polarity is simply a matter of looking for atoms that convey polarity.

For example, the compound propane (C3H8) could be shown like this:

CH3-CH2-CH3

This molecule (and all other unadorned hydrocarbon chains like it) is non-polar. There's nothing drawing electrons more strongly to one end of the molecule than the other.

Now consider the case of propanol (C3H7OH), which has a hydroxyl group on one of the terminal carbon atoms.

CH3-CH2-CH2-OH

Because the oxygen atom is so electronegative, it draws electrons to it. This molecule is more polar than propane.

I hope that helps, and good luck!

Answer 3

Polarity is determined by the dipole-dipole moment about a molecule. If a molecule has ligands (atoms bonded to it) that are different in their electronegativity, such as CH3Cl, it will be very polar. Chlorine's high electronegativity will give it a partial negative charge in the molecule as it pulls the electrons closer to itself and away from the carbon. A molecule like CH4, (methane), will be nonpolar. All the ligands attached to carbon have the same electronegativity, so there is no difference in dipole around carbon. Another determiner regarding polarity is the presence of lone pairs of electrons. Ammonia (NH3) has ligands that all have the same electronegativity. However, ammonia has a lone pair of electrons, so the dipole moment around ammonia is partially negative.

Answer 4

Determine the overall molecular polarity by considering the symmetry and electronegativity of its constituent atoms. If the molecule's electron distribution is uneven and does not cancel out due to symmetry, it is polar. If the electron distribution is even and the individual bond moments cancel out, the molecule is nonpolar.

Answer 5

Polar molecules usually have lone pairs and the central atom is bonded to more than 1 atom.

Nonpolar molecules usually have symmetrical bonds. An example of this is CH4. Everything cancels the partial charges out, making the molecule nonpolar. Also if the molecules are the same as H2 they are nonpolar since they have the same electronegativity.

Answer 6

A polar molecule is a molecule that has a net dipole moment due to its having unsymmetrical polar bonds.

There are two factors that go into determining if a molecule is polar or not. To determine if a molecule (or ion) is polar or non-polar, you must determine both factors.

1) The polarity of the individual bonds in the molecule;

2) The shape or geometry of the molecule.

First, to determine if a given individual bond is polar, you need to know the electronegativity of two atoms involved in that bond. To find the electronegativities of all the elements, look at the periodic table (follow the link to the left of this answer under Web Links). If the electronegativity of the two atoms has a difference of 0.3 or less, then the bond is non-polar. If the electronegativity difference is greater that 0.3 but less than 1.7, then the bond is polar. If the two values have a difference greater than 1.7, then the bond is ionic, which is just very very polar.

Once you know which bonds in the molecule are polar and which are non-polar, you must use the shape of the molecule. You need the shape because two polar bonds, if oriented correctly can cancel each other out (like two equally strong people pulling in opposite directions on a rope -- nobody moves). There are 3 possible outcomes:

-- If all bonds are non-polar, then the whole molecule is non-polar regardless of its shape.

-- If there is symmetry in the molecule so that the polarity of the bonds cancels out, then the molecule is non-polar. A common example of this is carbon dioxide, or CO2. The molecule is linear, and its Lewis dot structure is like this: O=C=O (this doesn't include two sets of lone pairs on each oxygen). The carbon-oxygen bond is a polar bond, but because they are exactly opposed to each other, the molecule is overall non-polar. Another example of this is CCl4, where each carbon-chlorine bond is polar, but the molecule is non-polar. Here, how they cancel out isn't as obvious, but they do. CCl4 is a tetrahedral molecule, and the 4 C-Cl polar bonds cancel each other out.

-- If there are polar bonds but there is no symmetry such that they cancel each other out, the overall molecule is polar. Water is a typical example of this. The two O-H bonds are oriented in a V-shape, and so the don't cancel out. Similarly, CH3Cl is also polar. It is the same shape as CCl4 (see above), but now it doesn't have the same symmetry because there is only one C-Cl bond and the bonds don't cancel out anymore.

Answer 7

Alternatively, you can calculate partial charges and determine dipole moments. If the dipole moments cancel, it's a nonpolar molecule.

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The polarity is determined by the electronegativity of atoms in a molecule, chemical composition, chemical structure.

Answer 8

There are several ways to determine if a molecule is polar or nonpolar. One of these ways is to use the Lewis structure to determine the molecular geometry. A symmetrical molecule is nonpolar, while an asymmetrical molecule is polar.

Answer 9

polar *occurs between nonmetal and metal atoms

*is an unequal sharing among electrons

*has a moderate electronegativity

nonpolar

* occurs between nonmetals

* is an equal or almost equal sharing of electrons

*has almost no electronegativity

Answer 10

One way would be to look at the geometry and the relative electronegativity differences of the atoms making up the molecule. This requires a certain amount of practice.