What is electronegativity?

Electronegativity is the ability of an element to attract a shared pair of electrons towards itself. The greater the electronegativity of the element, the more the element will attract the electrons in a covalent bond towards itself. The trend of electronegativity in the Periodic Table is:

• Electronegativity increases across a period

• Electronegativity increases up a group

  
  

  
  

  The elements in red are the most electronegative elements, according to this trend. 

  This means that fluorine is the most electronegative atom, followed by oxygen, nitrogen and chlorine. 

  
  

  F > O > N > Cl 

  
  
  
  

  A more detailed explanation of electronegativity involves the following factors: 

  1. Nuclear charge of the atom (more protons = more ‘pull’ of negatively charged electrons)

  2. Distance between the nucleus and electrons in the outer shell (greater distance = less attraction between positively charged nucleus and valence electrons)

  3. Shielding of the nuclear charge by electrons in the inner shells (more shells = more shielding between nucleus and valence electrons =  less attraction between positively charged nucleus and valence electrons)

     Fluorine has an electronic configuration of 1s2  2s2  2p5. To achieve a stable octet configuration of 2p6, it strongly attracts electron pairs towards itself. Other elements in the same period do not have this configuration as they have fewer electrons in their 2p orbitals, so there is not that much attraction for them to pull the electrons towards themselves. 

     The size of the fluorine atom is very small, as the size of atoms decreases as we move across a period. This means fluorine’s 2p electrons are very strongly attracted towards the nucleus, which means the nucleus can ‘hold on’ to the electrons of fluorine and additionally attract the shared pair of electrons towards itself as well. As you go down the periodic table, the electronegativity will decrease as the distance between the nucleus and the outer shell of electrons and the covalent bond increases, so there is not as great an attraction.

     Finally, the only ‘shielding’ that occurs in a fluorine atom is by the 1s electrons, meaning fluorine is still deeply attracted to the nucleus. As you go down the periodic table, there is more shielding as electrons are filling higher shells, therefore reducing the elements’ electronegativity. 

     
     

     All these factors explain why fluorine (and it’s surrounding elements) are the most electronegative atoms.