Polar, Non-Polar, and Ionic Compounds: Explanation, Examples, and Practice

to understand polarity will first look at individual chemical bonds and then the entire molecule let's look at polarity between two atoms first each atom has a specific value for its electronegativity to figure out if a bond is polar or nonpolar we look at the difference between these values let's look at a condensed periodic table with the values we'll use most frequently let's try HCl hydrochloric acid hydrogen has a value of two point two oh and chlorine has a value of three point one six the difference between these two point two oh minus three point one six gives us zero point nine six that's the difference in electronegativity for H and cl but what does that number mean chemical bonds can be classified along a continuum if the difference in electronegativity is above two point zero it's an ionic bond we consider molecules between two point O and point five to meet polar and below point five is nonpolar these are just guides you may be given slightly different values back to HCl we found the difference in electronegativity to be zero point nine six meaning that HCl is considered a polar molecule other examples of polar molecules h f HB r and h i we've been talking about electronegativity electronegativity often written as e n is the ability of atoms to attract shared electrons those are the electrons that are between atoms when we draw Lewis structures as we've seen in the periodic table atoms have different values for electronegativity the trend is that atoms are more electronegative as you move towards fluorine or group 18 the noble gases they rarely form chemical bonds and we don't really consider their electronegativity to be important so we know HCl is a polar molecule with its difference in electronegativity greater than 0.5 but less than 2.0 for something like n to nitrogen gas we can look up the value for n which is three point zero four so three point oh four minus three point oh four is zero back to our continuum we see that a difference below 0.5 is nonpolar covalent at this point you probably realize you need to memorize the numbers in our continuum when we have diatomic molecules like Oh 2 + 2 F - these will always be nonpolar because the difference when we subtract the electronegativity values will be zero pause and take a moment to figure out if each one of these molecules is polar or nonpolar for HF we have a difference of one point seven eight meaning this is going to be a very polar molecule with those shared electrons spending most of their time around the fluorine atom for B RCL the difference is zero point two zero we can have different atoms and still have a non-polar bond for i2 they're the same we'll have an electronegativity value of 0 that means i2 is nonpolar we can now find the bond polarity between two atoms and even do simple atoms like HCL or n2 next up we want to look at polarity in larger molecules it's useful to follow these steps first have the Lewis structure second we'll look at the individual bonds just like we've been doing in this video and finally we'll look at the shape and the cemetry to figure out if the molecule is polar or nonpolar overall we'll start with ccl4 carbon tetrachloride carbon has a value of two point five five and cl has a value of three point one six the difference between these two numbers is zero point six one so we know that each bond is going to be polar we can write the structure like this the arrows point towards the more electronegative atom the Delta symbol that shows the charge here CL has a negative charge because it's more electronegative at this point we've looked at the Lewis structure and we've calculated the electronegativity difference between the bonds each carbon chlorine bond is polar but be careful this alone won't tell us if the whole molecule is polar or nonpolar we need to consider the symmetry of them molecule to answer that question ccl4 is a symmetrical molecule so watch what happens we have a carbon here in the center and we're gonna add chlorines so we add one chlorine and then we add the second one and they spread out they push away from each other the reason they do that is this atom here the surface are all the electrons and electrons are negative so when I try to put two negatives together they'll spread out if I add another one they spread out again you can see that they're equi distance and finally I'll add the fourth CL so we have CCL 4 and they're spread out in this tetrahedral structure this is symmetrical any angle you look at it it's pretty much the same that means that the surface of the molecule will be the same everywhere there'll be no pulse and it won't be polar tetrahedral shaped molecules will be nonpolar if they consist of carbon and four of the same type of atoms attached to that carbon using the steps we've just covered pause and try to figure out if ch3cl is polar or nonpolar for ch3cl we have the Lewis structure here and we can calculate the en difference for each of the bonds you can see that CCL that's a polar bond well to see a CH bond is nonpolar so with our Lewis structure we can take and look at the actual shape of the entire molecule we see we have the carbon with four atoms attached and we know those are going to spread out and form a tetrahedral structure we can see that we have two sides to this molecule we have a side with the chlorine atom which is more electronegative and that means those shared electrons between the chlorine and the carbon will spend more time around the chlorine atom making it more negative that means we have a negative Pole and a positive Pole and a polar molecule up until now we've only talked about electrons that are between atoms they're bonded electron pairs we also have pairs of electrons that are called unbonded electron pairs or lone pairs they are not in between atoms but they do have their own orbitals and that means they influence the shape the polarity and the symmetry of a molecule NH 3 is an excellent example first we'll draw the lewis structure for NH 3 next we can calculate the differences in electronegativity between bonds and we see that the NH bond is indeed polar but let's go back and look at the shape of the molecule to see if it's symmetrical we have our nitrogen atom in the middle and let's add three hydrogen atoms as we add them they spread out to be as far away from each other as possible and we have this structure when you look at it it looks like it should be nonpolar each of the hydrogen's is pulling in an opposite direction and they should cancel out but we need to go back to our Lewis structure because we have a lone pair of electrons we have to consider when we add the lone pair it influences the shape it actually pushes down the hydrogen's and now we have a pyramidal also called pyramidal structure so the structure is no longer symmetrical and that means we're going to have a positive and a negative side and we're going to have a polar molecule it's important to stress that polarity results from an unequal sharing of electrons the ones that are bonded shared between atoms but it also results from the shape or the cemetry of the molecule and this can be influenced by unbonded electrons like we saw with NH 3 let's take a look at one more pause and determine if h2o is a polar or nonpolar molecule will first look at the lewis structure for h2o and then we'll calculate the difference between bonds we can see that that h o bond that's a polar bond next let's look at the shape of the h2o molecule to see if we have symmetry so we'll start with our oxygen atom and we'll put two hydrogen atoms on that they spread out to be as far away as possible from each other and it looks like it would be symmetrical like these two hydrogen's would cancel out however we have our lone pairs two of them we'll put one two and now we can see that the molecule is no longer symmetrical we have a distinct top and bottom because we have this distinct top and bottom to the molecule water is a polar molecule polarity is a hugely important topic in science everything from medicines to building materials how the molecules interact is largely a function of their polarity to figure that out we drew the Lewis structures then we looked at the individual bonds the electronegativity difference between those bonds finally we looked at the shape and the symmetry including those lone pair electrons to figure out if the molecule was polar or nonpolar this is dr. B with polar and nonpolar molecules and thanks for watching

Channel: Wayne Breslyn

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Keywords: polar vs nonpolar, polar and nonpolar molecules, difference between polar and nonpolar, polarity, symmetry and polarity, molecule shape and polarity, electronegativity values, electronegativity and polar molecules, polar molecules, nonpolar molecules, finding if a molecule is polar or nonpolar, polar non-polar, polar non polar, polar and nonpolar bonds, polar and nonpolar covalent, polar covalent, ionic, polar, nonpolar, non-polar, non polar

Id: OHFGXfWB_r4

Length: 9min 36sec (576 seconds)

Published: Thu Dec 14 2017