Polarity of Molecules

[Hayden Lee 1C]

When looking at the Lewis structure for a certain molecule, how can we determine its polarity? I know polar bonds occur due to differences in electronegativity between atoms, but how would we determine the polarity of a molecule without knowing the specific electronegativities of its atoms? Thanks!

[SophiaBarden 2E]

You will always be provided with a Periodic table in which you can determine the charge difference between atoms. A higher charge difference between two atoms will mean the electrons in the covalent bond are not exactly equally shared. Using the Periodic table and charges from there, you should be able to tell whether a molecule will be polar, and which atom is pulling the electrons more. The more electronegative ion will pull the electrons in the covalent bone tighter to itself, results in a slight negative charge, while the atoms farther from the electrons will have a slight positive charge. This results in the molecules polarity.

[Jordan_OBrien_2k]

Symmetry is also a good way to indicate a molecule's polarity. If it is symmetrical, I believe that it is generally nonpolar. Having an electronegativity difference of >2 also means that it is ionic and <1.5 means that it is covalent.

[Anh Trinh 1J]

Adding on to this, nonpolar molecules are usually when there are 2 nonmetals of the same element, or when the electrons are share equally within a molecule.

[Silvi_Lybbert_3A]

You do not have to know the exact electronegativities of the atoms to know whether the molecule is polar or non polar. You only need to know the periodic trend and, if looking at a molecule and not just a single bond, also the shape. The periodic trend is that electronegativity generally increases as you move up and to the right of the periodic table (the most electronegative atoms in top right of periodic table). Polarity comes from a difference of electronegativity, so any bond between two different atoms will have some polarity; however, one generally accepted rule is that a covalent bond is only considered significantly polar if the difference in electronegativity between the two atoms is above 0.4. When looking at a molecule, make sure to factor in the shape of the molecule and if the dipole moments of the bonds will cancel out due to its geometry; if this is the case, the molecule will be non polar even if the bonds within it are polar.

[Kaihan_Danesh_2J]

I think you just need to know the trends. The trends are especially useful for questions that ask, for example, whether NH3 has molar polar bonds or HF. HF would have molar polar bonds because fluorine is more electronegative than N and since H is the constant in each, the difference in electronegativity between F and H is much higher than the electronegativity difference between N and H.

[Anastasia Yulo 1C]

When looking at the lewis structure, polarity can be determined from the symmetry of the lewis structure. The more symmetrical the appearance of the lewis structure is, the more likely it is to be polar. Also, knowing the electronegativity of each element (from the trends) is a consistent reliable way to determine the polarity of a molecule.

[Jacob Schwarz-Discussion 3I]

If the central atom is bonded to a more electronegative atom, the central atom will be pulled towards that atom, creating a polar atom. The symmetry of an atom also determines whether the molecule is polar. If the molecule is symmetrical, it is likely non-polar, and vice-versa

[oliviahelou]

Look at the bonds between the atoms, and compare the electronegativity between atoms

[Alan Nguyen 2I]

The difficult thing about determining whether a molecule is polar or not is that you must have a strong grasp on drawing Lewis structures and VSEPR theory in order to analyze some more difficult molecules. Often times, they will not give you the electronegativities of individual atoms on exams, relying on you to determine the difference in electronegativities based on periodic trends. These are two things that I would into when answering these types of questions!

[Neha Jonnalagadda 2D]

Polarity of a molecule can be determined by looking at the individual atoms' electronegativities. The higher the electronegativity, the more polar negative that part of the atom is. A diagram can be drawn showing the molecules overall polarity based on the location of the most and least electronegative atoms.