As one of the most important inorganic molecules, water’s significance in assisting biological processes are mostly attributed to its physical and chemical properties.
The main properties include:
- Polarity
- Cohesion
- Adhesion
- Surface Tension
- Capillary Action
- Specific Heat Capacity
In this blog, we will discuss about those properties and how they can create much more complexity in our lives.
Water is polar, meaning that it is covalent (sharing electrons due to similar electronegativities), but its geometric structure creates a “pull” towards a specific atom of the molecule.
The polarity is due to its overall partial negative charge created by the angular/bent shape of the molecule .
(for more information about this, check out molecular theory and/or VSEPR theory. It will be part of your AP chemistry curriculum)
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Most of water’s properties are due to hydrogen bonding.
Hydrogen bonding is an intermolecular attraction between an hydrogen from one molecule and an electronegative atom from another molecule, causing them to “stick” closer together.
Hydrogen bonding occurs when the partial positive of hydrogen becomes attracted to the partial negatives in electronegative atoms such as Nitrogen (N), Oxygen (O), and Fluorine (F).
Hydrogen bonding usually occurs with polar covalent molecules (not nonpolar) because it has a partial charge for attraction.
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So What Role Do Hydrogen Bonds Play in Properties of Water?
While Hydrogen Bonds are individually weak, it cumulatively creates very prominent characteristics:
Cohesion: The cumulative sticking together/hydrogen bonding of many water molecules.
An emergent property of cohesion comes:
Surface Tension: Due to Cohesive forces, surface tension is created, forming a water "bead" that takes up minimal surface area as possible and making it harder to break the attraction of the water molecules.
You can see these on beads when rain falls onto a window pane.
Adhesion: The sticking together/hydrogen bonding between water molecules and a different type of substance (not water).
The other substance is usually hydrophilic ("water-loving" in greek), meaning that it has a certain pull to attract water, such as other polar substances and ionic substances.
An example would be water sticking onto pine needles.
Capillary Action: This is a combination of adhesion and cohesion, where adhesion force is greater than cohesion, allowing water to rise up a hydrophilic substance.
Note that it does not usually work with hydrophobic substances (avoids water, therefore are usually nonpolar molecules such as lipids or waxes).
This combination of sticking between waters and sticking between water and the substance creates an upward pull.
The narrower the tube, the higher the water rises due to less surface area for water to fill.
High Specific Heat Capacity: It takes a great amount of energy to raise 1 kilogram of a substance by 1 C (unit of joule/kg/℃ or calorie/kg/℃).
In water, the cumulation of hydrogen bonds and vaan der waals (temporary attractions between any type of molecule) make it harder for heat to alter the temperature of water.
Why?
The cumulative attraction between water molecules makes it much harder for water molecules to move at a quicker rate, therefore enough heat must be absorbed into the system to break those hydrogen bonds and raise the temperature.
This means that large bodies of water (like oceans or big lakes) absorb a LARGE amount of heat from the sun without changing its temperature significantly.
Have you noticed how coastal places feel much nicer than areas from the Midwest during the summer? It is because the ocean is able to absorb the heat from the environment.
During the winter, the opposite happens: energy is released from the system to form hydrogen bonds, cooling off the water and warming the environment.
Evaporative Cooling: when water evaporates, it carries off the energy with it.
This is why we need to sweat; water is able to cool off our skin due to its high heat of vaporization and its compatibility with our human bodies.
Vocabulary Words (Bolded):
Adhesion: The sticking together/hydrogen bonding between water molecules and a different type of substance (not water).
Capillary Action: a combination of adhesion and cohesion, where adhesion force is greater than cohesion, allowing water to rise up a hydrophilic substance.
Cohesion: The sticking together/hydrogen bonding of many water molecules.
Electronegativity: The measurement of tendency to acquire electrons
Emergent Property: A new phenomenon that rises from a smaller phenomenon
Evaporative Cooling: The process of cooling a surface due to the evaporation of water (changing from liquid to vapor form due to heat)
Heat of Vaporization: measurement of heat to turn liquid to vapor at any given temperature
Hydrogen Bonding: a weak attraction of a hydrogen from one molecule to an electronegative atom from another molecule
Hydrophillic: Water-loving
Hydrophobic: Water-shunning; tends to not mix with water due to its lack of attraction
Intermolecular: Taking place between molecules
Specific Heat Capacity: Amount of energy or heat it takes to raise 1 kilogram of a substance by 1 ℃ (unit of joule/kg/℃ or calorie/kg/℃).
Surface Tension: A cumulation of forces form a water "bead" that takes up as minimal surface area as possible and making it harder to break the attraction of the water molecules.
Vaan der Waals: temporary attractions between any type of molecule or ionic compound
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