Entry 2- Hydrogen Bond

Second Official Post (For Chemistry Journal)

What do you understand by the word: hydrogen? Water. Hydrogen bond refers to the attractive interaction of a hydrogen atom with an electronegative atom such as oxygen. The hydrogen is bonded to another atom which is electronegative.

Hydrogen bond can occur between molecules or even between the different parts in a molecule itself. It can also occur in inorganic molecules and organic molecules like water and DNA respectively. What causes the high boiling point of 100 degree Celsius of water is actually hydrogen bonding.

A hydrogen bond donor is a hydrogen atom attached to an electronegative atom which is typically fluorine, oxygen or nitrogen. A hydrogen bond accepter is the electronegative atom, ignoring whether it bonds with the hydrogen atom successfully. Ethanol is an example whereby hydrogen is bonded with oxygen.

Hydrogen bonding can also occur in the case when hydrogen is attached to carbon. The electronegative atom attracts the electron cloud around the nucleus of hydrogen and decentralized the cloud, leaving the atoms with a positive charge. When this strong positive charge attracts a lone pair of electrons (in this case, the hydrogen bond acceptor), a hydrogen bond is formed.

The hydrogen bonds’ length depends on its strength, temperature and pressure and the strength of the bonds is variable according to its temperature, pressure and bond angle etc.

Let us now look at one of the simplest hydrogen bond, which is one formed in the water. In a water molecule, two hydrogen atoms and one oxygen atom is present. The molecules in the water can bond with up to four other molecules as each oxygen molecule has a lone pair of electrons which can form a hydrogen bond with two hydrogen atoms from other molecules. The great strength and the large number of hydrogen bonds in the water lead to the high boiling point of water. A lot of energy is needed to break the bonds. Water is unique. It has oxygen atom which bonds with two lone pairs and two hydrogen atoms. This shows that the total number of bonds in a water molecule can go up to four. With more bonds, more energy is needed to break them.

Therefore, the high boiling point of water is caused by hydrogen bonds. For example, hydrogen fluoride also has hydrogen bonds. Hydrogen bond basically brings a hydrogen atom and an electronegative atom together. However, hydrogen bonding must not be confused with covalent bonding.