Intermolecular Forces, Soap, and Neurotransmitters by Megan

Have you ever wondered how soap works while washing your hands? What is going on chemically when it removes all that dirt, grease, and blood? Whoopsiedoodle, did I just say blood? Shhh…

Related imageThe germs which have accumulated on our hands are usually found in dirt or grease, which are held together by oils. As you may know, oil and water don’t mix. Have you ever seen the different layers it creates when you try to mix them? Water can dissolve most substances, but because oil molecules are attracted to each other more than water molecules, and the water molecules are much smaller, it takes a stronger intermolecular force to break their hydrogen bonds to accommodate the oil molecules. Soap acts as a middleman, attaching to both the water and oils.

When we mix soap with water, the sodium atom dissociates (or separates) completely from the soap molecule, leaving its one available electron with the oxygen atom, which becomes negatively charged. The positively charged sodium ion is attracted to the slightly negatively charged oxygen portion of the water molecule. This attraction is called an ion-dipole interaction, because the sodium ion is attached to one of the poles (opposites) of the water molecule. As the soap dissolves, hydrogen bonds form due to the attraction between the slightly positively charged hydrogen atoms in the water molecules and the negatively charged oxygen (Stengler, A.E., n.d.).


When the soap attaches a molecule of grease to a water molecule through weak London dispersion forces, a micelle – or ball-like structure of the non-polar tails of the molecules clumped in the center – is formed for every particle of grease carried away by the rinse water.  The negatively charged oxygen ion of the micelle’s soap molecules attach to the positively charged hydrogen atoms of the water molecules using hydrogen bonds. The surface tension of the water is reduced, and the micelle containing the grease (which is now attached to the water) goes down the drain (Stengler, A. E., n.d.).

You may now be wondering what intermolecular forces are. You know that they are involved in the attraction of molecules in soap, dirt, and water, and in simple mundane tasks such as washing our hands. But did you know that they are at play all around us in our everyday lives? Check out this cool video from Crash Course Chemistry, which you guys may recognize already. (I recommend watching the video 1.25 times faster by going to settings in the bottom right of the video and changing the speed.)


As we learned from the video, intermolecular forces are forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions). They vary in strength and contain:

  1. London dispersion forces/non-polar covalent-which are the weakest
  2. Dipole-dipole bonds/covalent (nonmetals sharing electrons)-the strongest force of these being hydrogen bonds
  3. Ionic bonds-metal and nonmetal (strongest)

Depending on the strength of the attraction, they will affect various physical properties such as melting point, boiling point, vapor pressure, evaporation, viscosity (measure of liquid flow resistance), surface tension, and solubility (ability to dissolve) ( Ophardt, C. E. 2003). Of these 4 primary intermolecular forces, I’m only going to be talking about the first 3.

London Dispersion Forces

These forces are typically found in noble gases (Helium, Neon) and nonpolar molecules (carbon dioxide, oil) between regions of high and low electron density, so the greater the amount of electrons clustered together, the greater the strength of the attraction.

When two molecules come close together, their variations in charge can create a situation where one end of a molecule might be slightly negative and the other end could be slightly positive, resulting in a slight attraction of the two molecules (“Intermolecular forces”, n.d.). 

London dispersion is considered the weakest force because it is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles, or molecules with opposite concentration of charges (“London Dispersion Forces”, n.d.).

Dipole-Dipole Attractions


A dipole, or separation of charges, has a stronger attraction than a dispersion force, but it is stronger when more electrons or a larger dipole are present, resulting in permanent dispersion as they attract or repel opposite charges in the polar molecules. This means that the molecule has electrical poles- one end has a partial positive charge and the other has a partial negative charge. In the Crash Course video, it compares Sherlock Holmes and his sidekick Watson, who have two seemingly different personalities but collaborate to solve mysteries.


Hydrogen Bonding


Hydrogen bonds are the strongest force of dipole-dipole forces between hydrogen and elements with strong electronegativity (such as nitrogen, oxygen or fluorine) in polar molecules.

*Electronegativity measures the tendency of an atom to attract a bonding pair of electrons (Clark, J., 2013) and the trend can be found using the trend on the periodic table- increasing across a row from left to right and increasing through a column or group from bottom to top.

These bonds are the strongest attraction that occur between molecules and are essential to living organisms as they maintain the structure of protein molecules and the double-helix structure of DNA molecules. The bonds are strong enough to hold DNA together, but are also weak enough to form and break readily to enable DNA to untwine for replication (“Intermolecular Forces”, 2001).dna-rna-chromosomes-double-helix-rotating-animated-gif-9

Life on Earth exists at least partly because of the hydrogen bond. The physical properties of water, which makes up two-thirds of the human body’s mass, are largely due to its extensive network of hydrogen bonds. Hydrogen bonding and intermolecular interactions are the very basis of the genetic code and the unique structures and shapes of the nonaqueous components of life: DNA, RNA, proteins, and other biomolecules. These components that make up living systems all owe their form and function to hydrogen bonds (“Intermolecular Forces”, 2001).


Just as intermolecular forces can be related to our everyday lives in simple, mundane tasks such as washing our hands, they can also be related to psychology, the study of the mind and its processes which affect behavior. These processes include the release and re-uptake of neurotransmitters, such as serotonin (which helps to regulate our emotions and moods) and endorphins, which we’ve all felt after a strenuous run or exercise when we push our bodies to expend more energy and effort.

All the feelings and emotions that people experience are produced through chemical changes in the brain. The “rush” of happiness that a person feels at getting a good grade on a test, winning the lottery, or reuniting with a loved one occurs through complex chemical processes. So are emotions, such as sadness, grief, and stress. When the brain tells the body to do something, such as to sit down or run, this also sets a chemical process in motion. These “chemical communicators,” or neurotransmitters, are the “words” that make up the language of the brain and the entire nervous system (Brain Chemistry, 2016).

Image result for abstract neuron wallpaperThe human brain is composed of billions of cells, each a separate entity that communicates with others. The chemical interaction of those cells determines personality, controls behavior and encodes memory (Sweedler, J., 2011).

Chemistry relates to psychology because these chemicals facilitate or inhibit the transmission of impulses from one neuron, or nerve cell, to another in our nervous system. The way they relay messages and convey signals to other parts of our bodies affects our moods and behavior. In order for them to communicate efficiently with our brain and our body on how to act, the brain has to send out chemical information that allows it to carry out its daily functions, such as generating movement, speaking, thinking, listening, regulating the systems of the body, and countless others. If these chemicals are out of balance, they can cause various psychological problems such as depression or bipolar disorder (“Brain Chemistry”, 2016).

 Image result for Information transmission within the brain, such as takes place during the processes of memory encoding and retrieval, is achieved using a combination of chemicals and electricity. It is a very complex process involving a variety of interrelated steps, but a quick overview can be given here.

As we can see in the picture, the neuron sends out electrical impulses which carry the neurotransmitters, and much the same way that soap works, these molecules will fit into particular receptors appropriately like a lock and key in the synapse. Just like intermolecular forces, the molecule exerts certain forces on its environment. For example, the “feel good chemical” dopamine is sent from a neuron and released into the synapse where it connects with receptors and activates the receiving neuron, which in turn can pass the message on to the next neuron, creating a chain reaction that produces pleasure. The more dopamine that floods the system, the stronger and more intense the reward is. The neurons communicating with each other could be compared to a dipole interacting with another dipole, or an atom bound to the same atom through London dispersion. Just as the attraction is stronger depending on the force and the number of molecules, the amount of dopamine and pleasure felt are dependent on how many neurotransmitters are flooding the system and are being accepted in the synapse.

As you can see, it is important to realize that science and chemistry play into our lives much more than we are willing to give credit. The way our brain works affects our behaviors, and those of us that struggle to control our emotions or have an irregularity in our hormones/ neurotransmitters can benefit from medications such as antidepressants. The only way we can do that is by seeing a doctor, or someone who specializes in the academic field of medicine who can prescribe us drugs that help balance out the chemicals in our bodies and minds, and help lead to a more satisfactory life. This knowledge is applicable to my field of study as I want to become a nurse, so I have to understand the chemistry of the brain and body- how different parts work and react together- and the effect of the environment and forces around us, so that I can efficiently and effectively provide excellent care for every patient.



Brain Chemistry (Neurochemistry). (2016). Retrieved November 22, 2016, from


Clark, J. (2013, March). Electronegativity. Retrieved December 09, 2016, from

Intermolecular forces. (2001). In World of Physics. Gale. Retrieved from

Intermolecular forces. (n.d.). Retrieved November 22, 2016, from

London Dispersion Forces. (n.d.). Retrieved November 22, 2016, from

Ophardt, C. E. (2003). Physical Properties. Retrieved November 22, 2016, from

Stengler, A. E. (n.d.). How Does Soap Clean. Retrieved December 9, 2016, from,5078.1

Sweedler, J., H, W., & Lycan, J. (2011). New Techniques Study the Brain’s Chemistry,

Neuron by Neuron. Retrieved November 22, 2016, from

Image References

Steckler, S. (2016, February 11). Hand Washing [Digital image]. Retrieved November 21,

2016, from

[Water spinning down drain]. (2015, January 07). Retrieved December 9, 2016, from


Green, H. [CrashCourse]. (2013, August 13). Liquids: Crash Course Chemistry #26 [Video file]

Retrieved December 9, 2016, from

C., & K. (2013, August 15). London dispersion forces [Digital image]. Retrieved November

13, 2016, from


Bertrand, G. L. (n.d.). Dipole-Dipole Interaction [Digital image]. Retrieved November 4,

2016, from

Sherlock Holmes [Cartoon]. (2013, March 10). In Ghost Bees. Retrieved November 13, 2016,


Hydrogen Bonding in Water [Digital image]. (2001, August 13).


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