Write the Lewis structure for each molecule. a. PH₃

Video transcript

Hello everyone today. We are being asked to draw a reasonable lewis dot structure for phosphorous tri chloride or PCL three. So the first thing I wanna make notice of how many of each atom that we have. So we know that we have one phosphorus atom and phosphorus is in the fifth group on the periodic table and therefore has five valence electrons. This gives us a total of five valence electrons to work with tri chloride means we have three chlorides chlorine atoms. And because chlorine is in the seventh group on the periodic table, it has seven valence electrons giving us 21 valence electrons. And in total we have 26 valence electrons to work with. Next we must make note of the least electro negative adam that goes in the center so it goes in the center of the rest of the atoms. And according to the periodic table trend, the electro negativity increases as we go upward and to the right. So phosphorus would be considered least electro negative and therefore would be in the center surrounded by three different chlorine atoms drawn as such. We have now connected these four atoms with three bond lines and each bond line has two electrons. So we went from 26 valence electrons - to just 20 next we must make sure that we fulfill the octet rule and also the valence electron rule. So chlorine is in the seventh group. So it has seven valence electrons. And now we must draw six individual electrons around each chlorine atom to fulfill that rule. And so now each chlorine atom has eight total electrons but seven valence electrons. And so we've used 18 of our electrons and we only have two valence electrons. Left phosphorus is on the fifth group on the periodic table, as dated before, it has five valence electrons. So since it has three already directly attached to it, we must add the two remaining electrons. We're left with zero valence electrons and we have our structure for phosphorous tri chloride. I hope this helped. And until next time.