A bond formed by a shared pair of electrons with both electrons coming from the same atom

The bond you're referring to is known as a coordinate covalent bond, or a dative bond. Here are the steps to how it is formed:

1. A coordinate covalent bond is a special type of covalent bond. In a typical covalent bond, each atom contributes one electron to the shared pair. However, in a coordinate covalent bond, one atom provides both electrons.

2. The atom that provides both electrons is known as the donor atom, while the atom that accepts the electrons is known as the acceptor atom.

3. This type of bond often occurs when a molecule with a lone pair of electrons interacts with a molecule that needs two more electrons to complete its valence shell.

4. The donor atom shares its lone pair of electrons with the acceptor atom, forming a coordinate covalent bond.

5. Despite the unusual formation, once the bond is formed, it behaves like any other covalent bond. The shared pair of electrons is located in the space between the two atoms, holding them together.

6. An example of a molecule that can form coordinate covalent bonds is ammonia (NH3). The nitrogen atom in ammonia has a lone pair of electrons that it can share with other atoms or molecules.