Atoms/molecules
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3. Changing the way we think about electrons

Article 3 Module 2

Sphere within a sphere

An immense balancing act

Electrons - as negative particles - stay as far as possible from each other. This creates difficulty as electrons are also attracted to the nucleus.

That leaves electrons with their best option being when they pair up so that each has the lowest possible energy.  For example, energy is released when two hydrogen atoms come together - joining together their lone electrons. 

Hydrogen is the simplest atom; as all other elements have 2 or more electrons. Creating chemical bonds between atoms ends up being an immense balancing act. The multitude of electrons are fighting to maintain the lowest kinetic energy at the prevailing temperatures and pressures. 

Hydrogen molecular orbitals

Hydrogen molecular orbitals (bonding, lower figure, lower energy/antibonding, upper figure, higher energy)

There must be order for chemical bonds to exist

Let's take another relatively simple element: sodium. The element sodium is a soft silvery metal that can be easily cut, even with a kitchen knife. It is a very reactive element and creates an explosive reaction when placed in water. 

Sodium metal

How does that lone electron in sodium's 3s orbital dictate its bonding to other atoms? Here are two examples:  

  • In sodium metal, the electrons are delocalized! They no longer belong to one sodium atom, they are communal. In the image below on the left, the electrons circle around in between the positive nuclei,  like moths around a flame. 
  • However, the sodium in table salt (the image below on the right) has the sodium ion locked in between the chlorines; the sodium's lone electron has been captured by a chloride ion.
sodium metal bonding

sodium metal bonding

Sodium chloride bonding

sodium chloride bonding

Why do electrons in sodium choose those bonds? Clearly, the electrons have chosen positions that have the lowest kinetic energy. This is forcefully demonstrated when sodium metal is added to water.

The 3s orbital  electron of two sodium atoms and the 2s orbital electron of two hydrogen atoms of water drop down one energy level, like this: 

2 Na (3s electron) + 2 H2O (2s electrons) ---> 2 NaOH (2s electrons) + H2 gas (1s electrons)

The 3s electrons of the sodium metal have dropped to the 2s electron level ; the 2s electrons of two hydrogen atoms have dropped down to the 1s orbital level. This change in energy levels releases a lot of heat. That explains the violent reaction of sodium metal with water seen 1947 video clip of disposal of 20,000 pounds of sodium metal).

Diagrammatically, this is what the reaction looks like: 

Sodium metal and water

Sodium metal and water

Thus, the sodium metal creates a bond with the hydroxide ion of water; and two hydrogen atoms come together to form hydrogen gas.

There is a way to think of it, mathematically

It is hard to imagine how electrons form strong bonds when they are interacting within orbitals. How do they manage to keep order within the relative chaos and uncertainty of orbitals?

Is there a unifying paradigm that helps us visualize what is happening at the level of the electrons? A paradigm that explains bonds as diverse as metallic sodium and table salt?

I believe there is; In module 3, I will start explaining a paradigm for a simple mathematical representation of the kinetic energy of electrons. But, first, I'd like to go over the areas that this paradigm will touch on, in the next lesson.

Picture credits: 

  1. Kevin Dooley. Atom: Protons, Neutrons, Electrons, Probability. Flickr.com, taken on Dec 7, 2013,
  2. By Tatiana53. Sphere 3d. Shutterstock.com, ID: 10939195.
  3. ChiralJon. Hydrogen Molecule. Flickr.com, uploaded on April 6, 2019.
  4. Mrs Pugliano. sodium1. Urgitis, Justin. Sodium metal chunks under mineral oil.  Flickr.com, taken on Jan 12, 2011.
  5. By Emre Terim. Chemistry - Formation of metallic bond. Shutterstock.com, ID: 1440912644.
  6. By OSweetNature. Ionic compound, crystal structure with positive and negative ions. Shutterstock.com, ID: 1122169052.
  7. Juman Hijab. Schematic diagram of the reaction of sodium metal with water. Nov 2020.
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