Ionic, Covalent and Coordinate or Dative Bonding

There are two extreme cases of chemical bonding ionic and covalent. Ionic bonding occurs when there is a complete transfer of one electron from one atom to another to form ionsas in the equation  

In this case the electropositive sodium atom loses its 3s electron, which is then transferred to the 2p orbital of the electronegative fluorine atom to produce the Na+F ion-pair. Ionic bonding is the subject of Chapter 7. When there is little or no difference in the electronegativity coefficients of the combining atoms, covalent bonds are possible in which two or more electrons are shared between the two atoms. Covalency is the main subject of this chapter. 

The resulting adduct has the same number of valence electrons as the ethane molecule, C2H6, and has the same structure with the two parts of the molecule having rotational freedom around the N— B coordinate bond, or covalent C-C bond in ethane. Coordinate or dative bonds are usually drawn in molecular structures as arrows to represent the direction of the donation process as in donor atom— acceptor atom 

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