Chemistry · Structure Of Atom · NEET
Only two: d(x2-y2) and d(z2). The four lobes of d(x2-y2) point straight along the x-axis and y-axis. The d(z2) orbital has its main lobes along the z-axis (plus a ring in the xy-plane). These two are the along-axis d-orbitals.
Three of them: d(xy), d(yz) and d(xz). Their four lobes each point into the region between two axes, at 45 degrees. For example, d(xy) lobes lie in the xy-plane but between the x and y axes, not on them.
Look at the name. If the label has TWO different letters together (xy, yz, xz), the lobes are BETWEEN those two axes. If the label has a single axis squared (z2) or a subtraction of squares (x2-y2), the lobes are ALONG the axes. So two-letter = between, squared = along.
Between. Even though d(xy) lives in the xy-plane, its lobes point between the x-axis and the y-axis (at 45 degrees), so it is a between-the-axes orbital. Students often mix this up because 'xy' sounds like it should sit on both axes.
Both lie flat in the xy-plane, but their lobes point differently. d(x2-y2) has lobes pointing directly along the +x, -x, +y, -y directions (on the axes). d(xy) has lobes rotated by 45 degrees, sitting between those axes. So plane is the same, direction of lobes is different.
The two big lobes of d(z2) point along the z-axis (up and down). It also has a small doughnut-shaped ring (called a torus) in the xy-plane around the middle. Because the main lobes are on the z-axis, d(z2) is counted as an along-axis orbital.
In coordination chemistry (crystal field theory), the along-axis orbitals d(x2-y2) and d(z2) point straight at the incoming ligands, so they are pushed up in energy (the eg set). The between-axis orbitals d(xy), d(yz), d(xz) point away from ligands and stay lower (the t2g set). NEET has directly asked which pair lies along the axes.
Which of the following pairs of d-orbitals will have electron density along the axes?
Which one is a wrong statement?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Two: d(x2-y2) and d(z2). The remaining three, d(xy), d(yz) and d(xz), lie between the axes.
Along the axes. Its two main lobes point up and down along the z-axis, so it is an along-axis orbital.
In an octahedral field, the along-axis orbitals d(x2-y2) and d(z2) form the higher-energy eg set, and the between-axis orbitals d(xy), d(yz), d(xz) form the lower-energy t2g set.
They point straight at the negatively charged ligands, so electrons in them feel more repulsion and are pushed to higher energy. Between-axis orbitals point away from ligands and stay lower.
Yes, d(xy) lies in the xy-plane, but its lobes point between the x and y axes (at 45 degrees), so it is a between-axes orbital, not an along-axis one.
