What is catenation and what are two elements that exhibit the property of catenation?

Bonds are formed when two or more atoms share electrons with each other, usually to satisfy the octet rule which states that having 8 electrons in the valence shell confers stability. In the case where a bond is formed between the same atoms, the molecule is called a homonuclear diatomic. This is the case for oxygen gas (a diatomic atom of two oxygens bound to each other). 

Some atoms, meanwhile, are capable of forming long...

Bonds are formed when two or more atoms share electrons with each other, usually to satisfy the octet rule which states that having 8 electrons in the valence shell confers stability. In the case where a bond is formed between the same atoms, the molecule is called a homonuclear diatomic. This is the case for oxygen gas (a diatomic atom of two oxygens bound to each other). 

Some atoms, meanwhile, are capable of forming long chains by bonding with each other. This is called catenation. Catenation is the linkage of atoms of the same element to form long chains. Two famous and common examples of this are carbon and silicon. Other atoms capable of catenation are sulfur and boron. 

Silicon can form chains of `S_n H_(2n+2)`, but it is highly challenging to purify the compound for n greater than 8. Meanwhile, catenation in carbon is more ubiquitous. Carbon chains are prevalent in nature; this is the reason why carbon is important in life and survival of carbon-based beings. Carbohydrates and lipids contain tails of carbon chains of varying lengths. 

The reason why carbon has such special and unique properties is because of its valency and size. It has four valence electrons and is hence capable of sharing these with four other atoms to form four bonds. Moreover, being the smallest atom with this property, its bonds are strong.

In brief, catenation is the linkage of atoms of the same element to form long chains. Examples of atoms that form such long chains are carbon, sulfur, silicon, and boron. In a way, this property explains why carbon is very important in the persistence of life as we know it.