Bond Enthalpy in Chemical Bonding

In chemistry, a chemical bond is a strong interaction that exists between two or more atoms. The bond holds the atoms together and gives them a strong enough attraction to each other to allow them to be separated. This separation is also known as diffusion, and the atoms can then be moved around or changed into different chemical compounds. 

Bond enthalpy 

Bond dissociation energy, or bond enthalpy, is the amount of energy required to break one mole of a specific type of bond and split it into gaseous atoms. The greater the bond enthalpy, the stronger the bond.

Bond enthalpy is expressed in kJ mol-1

Factors affecting bond enthalpy

Take a look at the factors that play a major role and affect bond enthalpy:

1. Bond enthalpy is affected by atoms. The greater the atom’s size, the greater the bond length and less the bond dissociation energy.

1. Bond enthalpy is also affected by the presence of multiple bonds; the greater the number of bonds, the greater the bond enthalpy.

1. The number of lone pairs of electrons present on the bonded atoms also affect the enthalpy, as the repulsion is greater between the atoms and less is the bond dissociation energy. This is also one of the factors that affect bond enthalpy.
   
2. When atomic bonds overlap with each other, a bond is formed. The direction of bonding is determined by the direction of overlap.
   

The bond angle is formed by the lines representing the bond’s direction and affects bond enthalpy, i.e. the orbitals holding the bonding electrons.

Order of bond affects bond enthalpy as a three-electron bond is comparable to a half-covalent bond in an odd-electron molecule; the order of bond can be fractional.

The higher the order of bond, the more stable it is, i.e. the higher the bond enthalpy. The higher the bond order, the shorter the bond length.

The bond energy decreases in the following order: sp>sp²>sp³.

Atom reaction

Atoms are made up of a nucleus and electrons that surround them. The electrons organise themselves in shells surrounding the nucleus, with each shell holding a specific number of electrons. The atomic number determines how many electrons an atom has when it is created. The atomic number’s electrons fill the electron shells from the inside out, leaving the remaining electrons on the outside.

A molecule is formed when two or more atoms chemically bind together.

Three primary forces that hold atoms together in an atom are strong nuclear force, electromagnetic force, and weak nuclear force. The electrons are held to the atom by the electromagnetic force. Protons and neutrons are held together in the nucleus by the strong nuclear force. The weak nuclear force governs the atom’s decay.

Covalent bonding

A covalent bond is a chemical relationship that involves the sharing of electron pairs between atoms. When atoms share electrons, shared pairs or bonding pairs are the stable balance of attractive and repulsive forces. In contrast, covalent bonding is the stable balance of attractive and repulsive forces between them.

The sharing of electrons allows each atom in multiple molecules to achieve the equivalent of a valence shell, leading to a stable electronic configuration.

Examples of covalent bonding

Carbon, hydrogen, oxygen, and nitrogen are nonmetals that form covalent connections with one other or with other atoms. 

• Hydrogen (H2)

The simplest of all elements is hydrogen (H). It only has one electron and needs another to achieve the electrical configuration of helium, the nearest inert gas. Two hydrogen atoms will join together in a single bond to form a hydrogen molecule.

• Oxygen (O2)

The outermost (valence) shell of oxygen (O) has a valency of two, which implies it takes two electrons to complete. As a result, two oxygen atoms join and share their two valence electrons, forming a double bond.

• Nitrogen (N2)

Because nitrogen (N) contains five valence electrons, it requires three more to complete its octet. The combination of two nitrogen atoms will occur. Each will share three electrons to make three covalent bonds, resulting in a nitrogen molecule.

• Water (H2O)

Two hydrogen (H) and one oxygen (O) atoms make up a water molecule. The valency of oxygen is two, while hydrogen has just one electron in its orbital. As a result, each hydrogen atom will share an electron with the oxygen and form a covalent link. As a result, two single bonds will exist.

• Carbon dioxide (CO2)

Two oxygen (O) atoms are bound to a single carbon (C) atom in carbon dioxide. Carbon has a valency of four, while oxygen has a valency of two. As a result, each oxygen forms a double bond with the carbon by sharing two of its valence electrons. As a result, every C=O bond is a double bond.

• Methane (CH4)

One carbon (C) and four hydrogen (H) atoms make up methane. Carbon has a valency of four, while hydrogen has a valency of one. As a result, each hydrogen will share its single electron with the carbon and form a single covalent bond. In methane, there will be a total of four covalent bonds, all of which will be single bonds.

• Ammonia (NH3)

The outer orbital of nitrogen (N) possesses five electrons and requires three more to complete its valence shell. The lone electron of hydrogen (H) will be shared with nitrogen, and three hydrogen atoms are required to complete the outermost shell of nitrogen. Three single covalent bonds result from the sharing of electrons.

1.  Carbon Monoxide (CO)

Three covalent bonds connect the carbon (C) and oxygen (O) atoms in the carbon monoxide molecule. The outermost shell of carbon has a valency of four and will take four electrons to complete. The outermost shell of oxygen has a valency of two and requires two electrons to complete. As a result, the two atoms will create a normal double bond. Carbon is left with a two-electron deficit, which will be filled by oxygen, which already has lone pairs. The third covalent link will be a coordinate covalent bond as a result.