This model illustrates the typical features present in covalent and ionic chemical bonds. |
Consider the formation of a non-polar covalent bond between two atoms of hydrogen. Put the Covalent/Ionic Bond radio button to "Covalent" position, and put the Polar/Non-Polar radio button to "Non-Polar" position. Press Start. Note that the collectivization of the electrons occurs only when the atoms come close enough to each other. There are two electrons constituting an electron "cloud" surrounding the two nuclei. This bond is called a non-polar bond because the electron density is equal in both atoms. Press Reset. Put the Non-Polar/Polar radio button to "Polar" position, and press Start once again. Note that as hydrogen and chlorine atoms come close together, the chlorine atom - which requires only one more electron to reach the noble gas configuration - will take the electron shell (containing one electron) from the hydrogen atom. As a result, excess negative and positive charges form, appearing on chlorine and hydrogen atoms, respectively. This means that an HCl molecule is an electric dipole. Chemical bonds of the type that is found in an HCl molecule are called polar covalence bonds.
Bringing together the atoms of sodium and chlorine, - something that cannot be observed in our model as long as it operates in the ionic bond demonstration mode, - will cause the outer electron from the sodium atomic shell to pass over to chlorine. The number of electrons in a chlorine atom is only one electron lower than the total number required for it to reach the state of a noble gas, while a sodium atom has one electron that exceeds the number required to have a noble gas configuration. Therefore, sodium and chlorine atoms are transformed into Na+ and Cl- ions, in accordance with Coulomb's law. Composites of such type do not form molecules, but they have crystalline structure made up of positive and negative ions that are located alternatively in the corners of the crystal lattice.