When you think of a molecule as simple as methane CH4, you can see that it has four identical C-H bonds. Carbon has 6 electrons, 2 in 1s, 2 in 2s and 1 in 2px, 1 in 2py and 0 in 2pz. Interestingly, one of the electrons in 2 s goes to 2pz. How does methane form 4 identical C-H bonds with just 1 s and 3 p orbitals? The answer is that carbon uses hybridized atomic orbitals called sp3 that has 25% s-character and 75% p-character.
Molecular orbital theory can explain why we have triple bonds. For example, ethyne. The sigma bond formed by the sp-sp overlap along with the two perpendicular p-orbitals that are parallel with each other that form 2 pi bonds explains the triple bond.
I've also noticed that unpaired sp3 bonds like those in ammonia (NH3) are used to form bonds and paired sp3 are the lone pairs.
I was wondering how any of this knowledge is useful for someone wanting to find out about the physical properties of compounds? Do chemists think about these things?