Two Electron Groups Linear Geometry

Consider the Lewis structure of BeCl2, which has two electron groups (two single bonds) about the central atom  

Molecules that form only two single bonds, with no lone pairs, are rare because they do not follow the octet rule. However, the same geometry is observed in all molecules that have two electron groups (and no lone pairs). Consider the Lewis structure of CO2, which has two electron groups (the double bonds) around the central carbon atom  

According to VSEPR theory, the two double bonds repel each other (just as the two single bonds in BeCl2 repel each other), resulting in a linear geometry for CO2. Experimental observations confirm that CO2 is indeed a linear molecule. 

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