What do the + and - signs mean in p orbital lobes?

[hokhani]

In the attached figure, what is the physical meaning of signs + and - in opposite lobes of p orbitals?

 

[daveyrocket]

Those indicate the phase of the p orbitals. Recall that p orbitals have a node, so that, e.g. for the left one the function is positive to the right of the y-axis and negative to the left of the y axis.

 

[hokhani]

Those indicate the phase of the p orbitals. Recall that p orbitals have a node, so that, e.g. for the left one the function is positive to the right of the y-axis and negative to the left of the y axis.

Thank you. Do you mean that it is due to the radial part of wave function? If so, how to realize between p_x and p_y?

 

[daveyrocket]

No it's actually do to the angular part. px and py are just rotations of pz.