Why Is Ethylene Planar?

[alingy1]

Homework Statement

I just had my textbook tell me ethylene is a planar molecule. Not wanting to regurgigate crammed information, I'm trying to understand why the molecule has to be planar. Why can't two hydrogen atons located on one side be oriented in a perpendicular way to the two other hydrogen atoms located on the other side? I don't see why this model wouldn't be more stable.

Homework Equations

Theory of orbitals.

 

[chemisttree]

The pi bond must be oriented in a certain way for there to be orbital overlap. That and a simple molecular model will demonstrate to you why ethylene is planar

 

[DrDu]

Good question, especially in view of the fact that the higher analogues (with Si or Ge in place of C) aren't planar.