Polar Molecule: Definition And Examples

Polarity in chemistry refers to the unequal attraction of electrons in elements of a compound, resulting in a molecule with a negatively charged end and a positively charged end. The polarity of a molecule depends upon the electronegativity of the constituent elements of that molecule.

Elements that differ greatly in electronegativities will exert unequal attractions on electrons, creating a net difference in charge over the molecule. The polarity of individual bonds also determines a molecule’s shape as the unequal pull of electrons affects the spatial orientation of the molecules.

Polarity is an important concept as it determines the number of physical properties of a substance. The polarity of a substance determines its surface tension, solubility, and melting/boiling point. Polar molecules interact in characteristic ways via hydrogen bonding and dipole-dipole interactions.

Polar Bonds And Polar Molecules

Not all elements attract electrons with the same strength. Elements with a high electronegativity pull harder on elements with a low electronegativity. When two elements are bonded, the more electronegative element will exert a greater pull on the electrons. This causes the electrons to orient themselves closer to the more electronegative element. The movement of electrons creates a net difference in electrical charge and results in a molecule with a positively charged end and a negatively charged end.

Strictly speaking, kinds of chemical bonds can fall within two extremes, completely polar or completely non-polar. A bond that is completely polar involves one element taking an electron from another and is more correctly characterized as an ionic bond. Thus the term polar is most often reserved for covalently bonded compounds. When two elements have identical electronegativities, the electrons are pulled upon equally and the bond is non-polar. According to the Pauling scale, elements with an electronegativity difference of less than 0.5 make non-polar bonds and elements with an electronegativity difference between 0.5 and 2.0 make polar bonds. Any higher difference is considered an ionic bond.

Most chemical compounds are made of more than two atoms and so consist of more than one chemical bond. Molecules can be polar either due to the polar bonds the have or due to an asymmetrical geometric arrangement of non-polar bonds. Conversely, a molecule can be overall non-polar even if it has polar bonds, provided those polar bonds are spatially oriented to cancel each other out. Polar molecules interact primarily through intermolecular dipole-dipole interactions. The differently charged ends of a polar molecule will attract the charged ends of other polar molecules. Unlike covalent or ionic bonds, dipole-dipole interactions are not true chemical bonds as they do not involve the sharing of electrons. How strong theses attractive forces determine how difficult it is to melt or boil something. The stronger the dipole-dipole interactions, the more kinetic energy required to break those attractions, so the more heat required to melt or boil that substance.

The polarity of a molecule also determines how well it will dissolve, and how readily it will be dissolved in another polar substance. Strongly polar substances are able to “steal” molecules via attractive forces, causing polar solids to dissolve in polar liquids.

Examples Of Polar Molecules

Water

The most obvious example of a polar molecule is water. Water is composed of two hydrogen atoms and one oxygen atom. Oxygen is more electronegative than hydrogen and so exerts a stronger pull on the shared electrons. The conglomeration of electrons closer to the oxygen atom causes the oxygen end of the molecule to take on a negative charge while the hydrogen ends take on positive charges. The polarity of water molecules is responsible for a number of waters physical properties.

Positively charged hydrogen ends are attracted to the negatively charged oxygen ends of other water molecules. This strong electrostatic intermolecular attraction explains the relatively high boiling point of liquid water as the strong dipole bonds require a lot of kinetic energy to overcome. Intramolecular attractions from hydrogen atoms is a special kind of dipole-dipole interaction called hydrogen bonding.

Interactions between polar water molecules also explain the phenomenon of surface tension on a body of water. At the surface of water, polar interactions between the water molecules draw them together more strongly than polar molecules in the air above. The result is a “film” of highly attracted water molecules at the surface of the liquid. Water, in particular, has a high surface tension, strong enough to support insects and small animals.

Ammonia

Ammonia (NH3) is another common polar molecules. Ammonia has a pseudo-tetrahedral shape, with three base hydrogen atoms, a central nitrogen atom, and a single pair of electrons occupying the would-be 4th tetrahedral node. The presence of two unbonded electrons causes the molecule to be highly polar, as there is a distinct concentration of electric charges on the nitrogen end of the molecule. Because ammonia is highly polar, it will readily dissolve in a polar solvent such as water.

Ethanol

Ethanol, sometimes simply just called alcohol, is a polar solvent with a chemical formula of C2H5OH. Carbon-hydrogen bonds are non-polar so a molecule of ethanol is almost non-polar. The hydroxyl group attached to one of the carbon atoms is what gives ethanol its polarity. Both C-O and O-H bonds are polar in the direction of the oxygen atom. In addition, the oxygen atom has a lone pair of electrons opposite from the C-O and O-H bonds. Due to this polarity, ethanol is a versatile solvent used in a number of laboratory and industrial applications. The hydroxyl group at the end of ethanol also allows it to engage in hydrogen bonding like water.

About The Author

Alex Bolano

When Alex isn't nerdily stalking the internet for science news, he enjoys tabletop RPGs and making really obscure TV references. Alex has a Masters's degree from the University of Missouri-St. Louis.

Speak Your Mind!

READ THIS NEXT

Map Of Florida Gulf Coast (Panhandle)

Check out the Florida gulf coast map and you’ll see just how beautiful the panhandle is. Florida is a very unique state in that it is situated along the Atlantic Ocean and the Gulf of Mexico, but one well-known location is the Florida panhandle along the Gulf of Mexico. The Floridian panhandle is an unofficial […]

Unsaturated Soils On Mars And Their Role In Mars Colonization From A Geotechnical Point Of View

Major current projects that are currently underway to have humans on Mars for exploration and also for possible settlement and colonization are the Mars One project and NASA project. There are still several geotechnical engineering tasks that have to be considered for the realization of the planned forthcoming human missions on Mars. Geotechnical difficulties linked […]

Increased PPAR-Îł Expression To Help Regulate Obesity And Overweight

Accordingly to the World Health Organization (WHO), almost 2 billion adults were overweight in 2016. Of these, over 650 million were obese. Clearly, overweight and obesity have become a global emergency with serious health concerns for affected individuals. Indeed, being overweight or obese increases the risks of diabetes, hypertension, atherosclerosis, and cancer. Considering the health […]

Glycoalkaloids In Potatoes: The Effect Of Biostimulants And Herbicides

Solanum tuberosum L., also known as potatoes, are one of the most consumed vegetable crops in the world. Because of their nutritional value, potatoes’ quality and safety are very important. There is a potential danger for potato consumers due to some toxic compounds called glycoalkaloids (TGA – total glycoalkaloids), which accumulate in potatoes during growth, […]

Restored Oxbows As A Nutrient Reduction Practice In The Agricultural Midwest

Nutrient export from the Corn Belt of the United States is impacting rivers at local and regional scales and is contributing to the development of hypoxic conditions in the Gulf of Mexico. The extent of Gulf hypoxia is largely driven by nitrate-nitrogen loads delivered by the Mississippi River that is sourced from row crop agriculture […]

SSTS: An Intuitive Way To Search In Time Series

The syntatic tool for pattern Search in Time Series (SSTS) presents a novel approach to query search and pattern matching in time series. The proposed methodology delivers a more interactive and expressive way of matching the desired patterns in time series. Nowadays, data scientists have a plethora of tools at their disposal to manipulate and […]

Analyzing Enhancer Expression In Pan-Cancer Patients

A human body contains about 37 trillion (3.7 X 1013) cells [1] that originated from a single zygote. This developmental process is precisely controlled by thousands of genes to ensure each cell follows the proper cell fate during replication. However, no machine has a zero failure rate. When this cellular machinery is disrupted, cells might […]