These slides provide an introduction to s-p mixing in diatomic molecular orbital diagrams appropriate for students in a general chemistry course.
In particular, my students were looking for a tool to help them remember which ordering of orbital energies to use. I've always thought that the Z ≤ 7 order (with s-p mixing) looks like a tree. In office hours, a student pointed out that the "standard" (Z ≥ 8) ordering of molecular orbitals looks like a light bulb. Thus, because "it's only Christmas sometimes," the MO diagram with s-p mixing--which looks like a Christmas tree--is only used in a few cases. Light bulbs are used most of the time, so the MO diagram that looks like a light bulb is used for most diatomics.
A student should be able to determine which ordering of molecular orbitals to use in generating a MO diagram for homonuclear and heteronuclear diatomic molecules with and without s-p mixing.
A student should be able to qualitatively explain (1) why s-p mixing only occurs for some elements and (2) why s-p mixing increases the energy of the 2σ MO relative to the 1π MOs.
I teach primarily using chalk, with slides as needed, so I actually go back and draw the shapes (in colored chalk) over MO diagrams I've previously drawn on the board. The students are suprised and excited to see the shapes emerge.