{"id":2941,"date":"2011-11-15T12:00:11","date_gmt":"2011-11-15T12:00:11","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=2941"},"modified":"2025-11-15T09:16:18","modified_gmt":"2025-11-15T15:16:18","slug":"how_to_use_electronegativity","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2011\/11\/15\/how_to_use_electronegativity\/","title":{"rendered":"How To Use Electronegativity To Determine Electron Density (and why NOT to trust formal charge)"},"content":{"rendered":"

How To Determine Partial Charges<\/strong><\/p>\n

Last time <\/a>we talked about how electrons are the “currency” of chemistry and every reaction is a transaction of electrons between atoms. That means that if we really want to understand a reaction, we have to understand where the electrons are (and aren’t).<\/p>\n

There’s two factors to employ when doing this. The first is electronegativity<\/strong>. That’s what today’s post is about: using electronegativity to determine electron densities<\/strong>. (The second is resonance<\/a> – more on that in the next article<\/em><\/span>)<\/p>\n

I’m assuming you know how to draw Lewis structures and understand the concepts of electronegativity and formal charge<\/em><\/a>, as well as being able to interpret line drawings, but that’s it.\u00a0 If you’re not at that level, back up and read up on those concepts.<\/p>\n

\"Summary-how<\/a><\/p>\n

Table Of Contents<\/strong><\/p>\n

    \n
  1. How Do We Tell Where The Electrons Are? First, Draw The Lewis Structure<\/a><\/li>\n
  2. Second, Apply Electronegativity To Determine Partial Charges<\/a><\/li>\n
  3. Formal Charge Is NOT The Same As Electron Density<\/a><\/li>\n
  4. Bottom Line: Use Relative Electronegativities, Not Formal Charges, To Determine Electron Densities<\/a><\/li>\n
  5. Notes<\/a><\/li>\n<\/ol>\n
    \n

    <\/a>1. How Do We Tell Where The Electrons Are? First, Draw The Lewis Structure<\/h2>\n

    OK. Let’s start with the first question: how do we tell where the electrons are in a molecule?<\/p>\n

    The first skill is being able to draw proper Lewis structures for a molecule. To succeed in organic chemistry you absolutely need to be able to do this in your sleep. <\/strong>The Lewis structure should account for all the electrons around an atom, including the often-hidden lone pairs of electrons if applicable. Let’s have a look.<\/p>\n