Why Does Adding an Electron Change Chemistry?

Most recent answer: 01/15/2016

Q:
All the electrons are same in nature. Then how can increasing 1 electron in a element changes its physical & chemical properties?
- Kshitij Agarwal (age 17)
India
A:

Think of even a mechnical object, say a chain of links. Adding one more link, just like the others, could make a chain into a loop. Think of a stone arch. Adding one more stone at the top can make two unstable arms turn into a stable arch. Although atoms and molecules are quantum mechanical, they do share that type of dependence on their ingredients with those mechanical systems.

One of the big effects is that adding an electron will convert an uncharged atom into a charged ion. That makes strong electrostatic attractions or repulsion to other ions. Adding a proton (and some neutrons) to the nucleus and an electron makes an uncharged atom of a different element. It can have very different properties. For example, helium has two tightly bound electrons. There are no more states available for such tightly bound electrons so adding a plus charge to the nucleus and a negative electron (giving lithium) leaves an atom with one electron that can come off pretty easily. That's why lithium easily forms positive ions in solution, while helium stays uncharged.

Underlying all these effects is the Pauli exclusion principle, that says that electrons (and other fermions) can only have 0 or 1 particle in each quantum state. That means that as more of them are added they have to go into quantum states that are quite different from the previous ones. (see  )

Mike W.


(published on 01/15/2016)