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- Chemical Bonding or sharing of electrons with two atoms do not require that the shared electrons be located equally between the two atoms.
- In fact most often these electrons are located closer to one of two atoms.
- The more electronegative element has more desire for the electron thereby the shared electrons are located closer to this atom.
- Therefore, there is an uneven distribution of electron thereby making one end of the bond have more electrons (partially negative) and the other end have less electrons (partially positive).
- Remember: A bond is between two atoms only
A general rule of thumb for predicting the type of bond based upon electronegativity differences:
- If the differences in electronegativities (delta EN) is less than 0.80, the bond is non-polar covalent (shared electron are evenly distributed (meaning electrons are spending as much time anywhere between the two atoms when they are moving between two atoms)
- To draw a non-polar bond, one just write symbol of first atom, then the symbol "--" indicate a covalent bond, then the second atom symbol.
- If the difference in electronegativities (delta EN) is greater than or equal to 0.80, the bond is polar covalent (shared electrons spend most of their time closer to one atom vs. other atom when they are moving between the two atoms)
- To a polar bond, you do the same as the non-polar bond except you add an addition symbol. It is a symbol of the an arrow ( +--->) with a "+" sign on other end of arrow. This arrow is separate symbol located above the atoms where the arrowhead ( > ) end is over the more electronegative atom and the other end ( + sign) is over the least electronegative atom.
- If the difference in electronegativities (delta EN) greater or equal to 1.7, the bond is ionic (there are NO shared electrons, one atom is pulling other atom's valence electrons around it while other atom has lost those valence electrons).
- To an ionic bond, there is no symbols since the resulting basic unit or particles are ions and there are sharing of valence electrons. So most of the time, if someone asks to "show" bond polarity for ionic bonds you simply say ionic bond.
- In real life, there are no hard and fast cut-offs (i.e. greater than 1.7, ionic), it is a gradual change. You would need to know additional chemical concepts to be certain. Therefore, this is why we use the above cut-offs in 1st year chemistry.