Question #99352

1 Answer
Stefan V.
May 25, 2015

Chlorine exists as a diatomic molecule, #Cl_2#, in which two chlorine atoms share an electron to form a covalent bond and complete their octets.

http://ibchem.com/IB/ibnotes/04.2.htm

As an atom, chlorine is very unstable because it only has 7 electrons in its outersmost shell. In order to become stable, it needs to complete its octet, i.e. have 8 electrons in its outermost shell.

When chlorine bonds to metals, it will take an electron from them to become the chloride anion, #Cl^(-)#. That happens because metals, especially alkali and alkali earth metals, are willing to give up electrons to complete their octets.

For example, in sodium chloride, the chlorine atom will take one electron from sodium's outermost shell, forming an ionic bond and giving rise to the aforementioned chloride anion and to the sodium cation, #Na^(+)#.

http://itc.gsw.edu/faculty/speavy/spclass/chemistry/bonds.htm

So, as a conclusion, in #Cl_2# the two chlorine atoms share and electron, while in sodium chloride, #NaCl#, the chlorine atom takes an electron from sodium.

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