# Alternative explanation of ethene's pi bond [closed]

This tutorial about ethene's bonds has the following paragraph that I hope someone can paraphrase in a better way:

The pi bond dominates the chemistry of ethene. It is very vulnerable to attack - a very negative region of space above and below the plane of the molecule. It is also somewhat distant from the control of the nuclei and so is a weaker bond than the sigma bond joining the two carbons.

What does it mean by:

• "vulnerable to attack"?
• "negative region of space"?
• Just get yourself a good textbook and read about orbitals and electro- and nucleophiles. – Mithoron Oct 22 '20 at 14:22

Electrons are negatively charged. So they may attract positive charges. If a positive ion like $$\ce{H+}$$ or $$\ce{Br+}$$ approaches an ethene molecule, it will be attracted by this negative $$\pi$$ cloud. If this approach leads to the formation of a new bond between the ethene molecule and the coming ion, it makes sense to state that the coming ion attacks the ethene. One may also state that the $$\pi$$ cloud attacks the coming ion. In other words, it also makes sense to say that the $$\pi$$ bond of ethene is vulnerable to attack, at least more vulnerable than the sigma bonds in the plane.