Phase?

[psyxwar]

I've come across this term when looking at molecular orbitals, and it says that antibonding molecular orbitals are created when the constituent orbitals are out of phase or something along those lines (and bonding MOs are achieved when they are in phase). What does this even mean?

[nerdgasm]

I'm honestly not too sure on this myself, but I believe you have to consider orbitals as wavefunctions which are solutions to the Schrodinger equation. Thus, because wavefunctions have a property called 'phase' (just as regular waves also have 'phase'), it follows that orbitals have 'phase' as well.

So, you can think of antibonding molecular orbitals being created when two atomic orbitals combine in an out-of-phase way (it's basically like two waves adding destructively, due to being out of phase with each other), and bonding molecular orbitals are created when two atomic orbitals combine in an in-phase way (like two waves adding constructively, due to being in phase with each other).

[lzxnl]

I've come across this term when looking at molecular orbitals, and it says that antibonding molecular orbitals are created when the constituent orbitals are out of phase or something along those lines (and bonding MOs are achieved when they are in phase). What does this even mean?

Let's assume you have a 1s orbital. Well this thing looks spherical to me. Imagine you have two of these spheres. There are two ways they can combine; by adding (in other words adding the amplitudes) and subtracting. That's really it. Being "in phase" just means you add the two wavefunctions. This terminology arises from physics where waves that are in phase and interfere have their amplitudes added, while waves that are out of phase have their amplitudes subtracted.