Hello! my question is.

Cumulene has chemical formula C4H4 with 7sigma and 3pie bonds. the 2 outer C atoms have a hybridization of "sp2", the H atoms have a hybridization of "s", and the 2 C atoms in between have "sp" hybridization. As I figured out, there has to be 3 sets of hybridizations, s/sp2 , sp/sp2 , and sp/sp. But there is another one which is p/p hybridization. Where did this p/p hybridization come from? and what does it mean?

Thank you

The presence of p/p hybridization in cumulene is due to the unique bonding arrangement in the molecule. Cumulene consists of a linear chain of three carbon atoms, with a triple bond between each adjacent pair of carbon atoms.

To understand the p/p hybridization, let's consider the electronic structure of carbon. In its ground state, carbon has two unpaired electrons in separate p orbitals and two paired electrons in separate s orbitals. When carbon undergoes hybridization, it combines the available orbitals to form the required number of orbitals with the same energy, shape, and orientation.

In cumulene, the two outer carbon atoms each have three sigma bonds and one pi bond, resulting in sp2 hybridization. The hybridization of sp2 means that one s orbital and two p orbitals from each carbon atom combine to form three sp2 hybrid orbitals. These sp2 orbitals overlap with the orbitals of neighboring atoms to form sigma bonds.

The two carbon atoms in the middle, between the sp2-hybridized carbon atoms, have only two sigma bonds and two pi bonds. To achieve this bonding arrangement, these carbon atoms undergo sp hybridization. This means that one s orbital and one p orbital from each carbon atom combine to form two sp hybrid orbitals. These sp orbitals overlap with the orbitals of neighboring atoms to form sigma bonds.

Now, to answer your question about p/p hybridization: the p/p hybridization refers to the unhybridized p orbitals on the carbon atoms involved in the pi bonds. In the case of cumulene, there are two unhybridized p orbitals on each carbon atom involved in the triple bond. These unhybridized p orbitals interact and overlap sideways to form the pi bonds along the chain. This interaction of parallel p orbitals allows for the formation of the pi bonds that are characteristic of cumulene.

In summary, the p/p hybridization in cumulene arises from the unhybridized p orbitals on the carbon atoms involved in the pi bonds. This type of hybridization enables the formation of the pi bonds that contribute to the unique bonding arrangement in cumulene.

The p/p hybridization you mentioned does not typically occur in cumulene (C4H4). Cumulene is a linear molecule where all carbon atoms are connected by double bonds. The carbon atoms at the ends of the chain (outer C atoms) have a hybridization of sp2, meaning they form three sigma bonds and have one unhybridized p orbital perpendicular to the plane of the molecule. This unhybridized p orbital can participate in pi bond formation.

The carbon atoms in the middle of the chain (inner C atoms) have a unique hybridization known as sp. Each of these atoms forms two sigma bonds and has two unhybridized p orbitals. The two unhybridized p orbitals align perpendicular to each other and parallel to the chain of carbon atoms. This allows for the formation of two pi bonds.

It's worth noting that hybridization is a simplified description of electron orbitals in molecules. In reality, the electron density is distributed among atomic orbitals and is not exclusively confined to hybrid orbitals. Therefore, it's more accurate to describe cumulene as a molecule with alternating single and double bonds rather than specific sets of hybridizations like s/sp2, sp/sp2, and sp/sp.

So, in summary, cumulene does not involve p/p hybridization. The p orbitals involved in cumulene's structure are unhybridized p orbitals that participate in the formation of pi bonds.

The first and fourth carbon atoms are sp2 hybridized. The second and third carbon atoms are sp hybridized. There is no need to assume the hydrogen atoms are hybridized.

Hybridization is a scheme to explain the geometry around a central atom bonded to two or more other atoms. Each of the four C atoms is a central atom with sp2 or sp hybridization. Your reference to "hybridization sets" makes no sense.
Each of the four carbon atoms has a non-hybridized p-electron The four p-electrons form an extended π-electron system (cloud) which does not alter, or adds to the sp2 and sp hybridizations mentioned.