Within a sheet, ___________ hybrid orbitals are involved in the _________ bonding network framework. This leaves atomic _______orbitals to be involved in interactions between sheets. These interactions are responsible for stacking.

Within a sheet, sp² hybrid orbitals are involved in the planar bonding network framework. This leaves atomic p_z orbitals to be involved in interactions between sheets. These interactions are responsible for stacking.

Extra: This description is characteristic of materials like graphite, a form of carbon. Let's break it down for clarity:

1. Hybrid Orbitals: In chemistry, hybrid orbitals are formed when atomic orbitals mix to form new orbitals that are used in bonding. For example, an sp² hybridization occurs when one s orbital and two p orbitals from the same atom mix to create three new equivalent orbitals.

2. sp² Hybridization: In an sp² hybridization, the carbon atom's four valence electrons are distributed as three electrons in sp² orbitals and one electron in a p orbital. The three sp² orbitals lie in a plane at 120-degree angles to each other, creating a trigonal planar shape, which is the foundation of the planar bonding network in materials like graphite.

3. Planar Bonding Network Framework: This refers to the covalent bonds that exist within a plane of atoms. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane, creating a hexagonal arrangement with strong sigma bonds resulting from sp² hybridization.

4. p_z Orbitals: After hybridization, carbon atoms have a remaining p orbital (the one not used in the sp² hybridization). This unhybridized p orbital is typically oriented perpendicular to the plane of the sp² orbitals and is often labelled as p_z. The electron in the p_z orbital can overlap with p_z orbitals of carbon atoms in adjacent planes, leading to the formation of pi bonds.

5. Stacking Interactions: The p_z orbitals from atoms in neighboring sheets have weak interactions that are responsible for the stacking of these sheets, like in graphite. These are van der Waals forces, also known as London dispersion forces, which, while much weaker than the covalent bonds within the sheets, still help to hold the layers together. This kind of weak intermolecular interaction enables the layers in graphite to slide over each other easily, which is why graphite is used as a lubricant and in pencils to leave marks on paper.