Polar vs Non-Polar Covalent Bonds
2. Short Answer Test – Click Here
3. Kahoot! based on Video – Click Here
What is Polarity and how does a molecule attain this property called “POLARITY”????
Polarity is created when two atoms joined together by a covalent bond – share their electrons unevenly. This occurs when one of the atoms participating in the bond has a stronger affinity for the electrons – a higher electronegativity. This uneven sharing of the electrons in a bond creates what is called a POLAR covalent bond.
This is in contrast to NON-POLAR Covalent bonds where the electrons are shared evenly.
In NON-POLAR Covalent Bonds both atoms sharing electrons in a covalent bond have a similar “Affinity” (desire) for the electrons and so SHARE EVENLY.
With all the different atoms on the periodic table trying to figure out whether a bond between 2 of these atoms is polar or non-polar may seem like a daunting task… but when discussing molecules in the body it is actually quite simple to learn what molecules are polar and non-polar… and that is because only 4 atoms (Carbon, Hydrogen, Oxygen and Nitrogen) make up more than 96% of the mass of living things. These 4 atoms are therefore the only atoms that contribute significantly to polarity in the body. It is therefore quite easy to learn which interactions between these 4 atoms are polar and which are not by learning a few simple rules:
1. Any bond between two of the same atoms is always NON-POLAR because the same atom obviously always has the same electronegativity as itself.
2. Carbon and Hydrogen always form non-polar bonds when they bond with one another because carbon and hydrogen have similar electronegativities (they share there electrons evenly).
3. Oxygen has a higher electronegativity than both Carbon and Hydrogen so when these atoms bond together they form Polar Covalent bonds.
4. And similarly, Nitrogen has a higher electronegativity that both Carbon and Hydrogen so when these atoms bond together they form Polar Covalent bonds.
Common molecules with Non-polar and Polar covalent bonds
Now lets take a look at some common molecules in the body and see if they contain polar or non-polar bonds.
Lets start with the most abundant molecule in the body. Water – H2O. Water is a polar molecule because it is composed of an Oxygen bound to 2 Hydrogen’s. The oxygen is more electronegative and so holds the electrons tighter creating a negative pole in the molecule and the hydrogens hold the electrons less tightly and so create positive poles. As such it behaves like a magnet. Molecules like water, that are polar, interact well with other molecules that are polar because their magnetic poles draw these molecules together. However, non-polar molecules do not share this magnetic like property and so do not mix well with water or other polar molecules.
Water is a polar molecule because it is composed of an Oxygen bound to 2 Hydrogen’s. The oxygen is more electronegative and so pulls the electrons in tighter.
Lets now look at all the major classes of molecules in the body. Fats, Carbohydrates, Proteins and Nucleic acids in terms of their polarity.
We’ll start with Fats – Fats (otherwise known as lipids) are the only major class of molecules in the body that are NON-POLAR. For this reason they do not interact well with water or other polar molecules. We see this when we pour fats into water – they separate. Why???? What makes fats non-polar?? Let’s take a look at a fat molecule to see why.
Here is the fatty acid “stearic acid”. It is composed of a long chain of 18 carbons with hydrogens attached. All of the carbon-carbon bonds are non-polar and all of the carbon hydrogen bonds are non-polar.
The other classes of molecules in the body – carbohydrates, proteins, and nucleic acids – are POLAR. This is because they contain oxygen and/or nitrogen mixed in with the carbon and hydrogen atoms and this creates significant polarity.
Carbohydrates have a similar structure to fats – being composed of carbon chains with hydrogens attached. However, every carbon in a carbohydrate also has an oxygen attached. Oxygen forms polar bonds with both hydrogen and carbon so adding an oxygen to each carbon creates a large amount of polarity in these molecules. Therefore carbohydrates are polar molecules.
Proteins and Nucleic acids, the other major classes of molecules in the body are large molecules that contain significant numbers of polar covalent bonds and so are also POLAR molecules. This is because they contain oxygen and/or nitrogen mixed in with the carbon and hydrogen atoms and this creates significant polarity.
Proteins and Nucleic acids both contain many oxygen and nitrogen atoms mixed in with carbon and hydrogen. This creates a significant amount of polarity in these molecules so they are POLAR MOLECULES.
Two other very important non-polar molecules in the body are oxygen and carbon dioxide. Carbon dioxide is composed of carbon and oxygen so you may expect it to be polar, however, the small and symmetrical shape of this molecule actually make it a non-polar molecule.
Oxygen and Carbon Dioxide are two important gases in the body. Both these gases are NON- POLAR. You may expect the oxygen – carbon bonds in carbon dioxide to be polar, but this is an exception to the general rule. Carbon dioxides symmetry and small size make it a relatively non-polar molecule.
Therefore, of the main molecules in the body, the only class of molecules that are non-polar are FATS. The other major classes of molecules, carbohydrates, proteins, nucleic acids, as well as water are all polar molecules due to their large amount of polarity created from their abundance of polar covalent bonds.