A covalent bond is formed when pairs of electrons are shared between two atoms. It is primarily formed between two same nonmetallic atoms or between nonmetallic atoms with similar electronegativity.
Lewis Dot Structure
Lewis structures are also known as Lewis dot structures or electron dot structures.
These are basically diagrams with the element’s symbol in the centre. The dots around it represent the valence electrons of the element.
Lewis structures of elements with atomic number 5-8
Covalent Bonding in H2, N2 and O2
Formation of a single bond in a hydrogen molecule:
Each hydrogen atom has a single electron in the valence shell. It requires one more to acquire the nearest noble gas configuration (He).
Therefore, both the atoms share one electron each and form a single bond.
Formation of a double bond in an oxygen molecule:
Each oxygen atom has six electrons in the valence shell (2, 6). It requires two electrons to acquire the nearest noble gas configuration (Ne).
Therefore, both the atoms share two electrons each and form a double bond.
Formation of a triple bond in a nitrogen molecule:
Each nitrogen atom has five electrons in the valence shell (2, 5). It requires three electrons to acquire the nearest noble gas configuration (Ne).
Therefore, both atoms share three electrons each and form a triple bond.
Single, Double and Triple Bonds and Their Strengths
A single bond is formed between two atoms when two electrons are shared between them, i.e., one electron from each participating atom.
It is depicted by a single line between the two atoms.
A double bond is formed between two atoms when four electrons are shared between them, i.e., one pair of electrons from each participating atom. It is depicted by double lines between the two atoms.
A triple bond is formed between two atoms when six electrons are shared between them, i.e., two pairs of electrons from each participating atom. It is depicted by triple lines between the two atoms.
Bond strength:
– The bond strength of a bond is determined by the amount of energy required to break a bond.
– The order of bond strengths when it comes to multiple bonds is: Triple bond>double bond>single bond
– This is to signify that the energy required to break three bonds is higher than that for two bonds or a single bond.
Bond length:
– Bond length is determined by the distance between nuclei of the two atoms in a bond.
– The order of bond length for multiple bonds is: Triple bond<double bond<single bond
The distance between the nuclei of two atoms is least when they are triple bonded.
Covalent Bonding of N, O with H and Polarity
In ammonia (NH3), the three hydrogen atoms share one electron each with the nitrogen atom and form three covalent bonds.
- Ammonia has one lone pair.
- All three N-H covalent bonds are polar in nature.
- N atom is more electronegative than the H atom. Thus, the shared pair of electrons lies more towards N atom.
- This causes the N atom to acquire a slight negative charge and H atom a slight positive charge.
In water (H2O), the two hydrogen atoms share one electron each with the oxygen atom and form two covalent bonds.
- Water has two lone pairs.
- The two O-H covalent bonds are polar in nature.
- O atom is more electronegative than the H atom. Thus, the shared pair of electrons lies more towards O atom.
- This causes the O atom to acquire a slight negative charge and H atom a slight positive charge.
