Another way of representing molecules is using Couper notation. In this case, only the electrons that are involved in the bond between the atoms are shown. ... Using Couper notation, a molecule of water and a molecule of HCN would be represented as shown in figures Figure and Figure below.

What is the Couper structure?

In 1858, Scottish chemist Archibald Scott Couper published the first structural formula representation of a molecule in his paper On a new chemical theory. He used elemental symbols to represent atoms with lines placed between them showing bonds. Couper's structures were very condensed.

What is the Lewis structure of Cl2?

In the Cl2 lewis structure, one bond present between two chlorine atoms. As one bond contains two electrons, so 2 electrons are available for sharing. And each chlorine contains three lone pairs. So, the total lone pair is 6 that makes 6*2 = 12 unshared electrons.