[figure] Figure 1. electron probability density for 2s orbital [figure] Figure 2. wave function for 2s orbital Which of the following point in Figure 2 most accurately represents the nodal surface as shown in Figure 1?
- D
- B
- C
- A
Answer
(2) B
Solution
A nodal surface is a region where the probability density 2 is zero; this is possible only where = 0.
For the 2s orbital, 2s is positive near the nucleus, becomes zero at one distance and is negative beyond it — this sign change gives one spherical (radial) node (number of radial nodes = n − l − 1 = 2 − 0 − 1 = 1).
In Figure 2, 2s(x) = 0 (the curve cuts the x-axis and changes sign from + to −) at point B.
A is the maximum at the nucleus, C is the minimum (most negative ψ) and D lies in the negative region; at none of these is ψ zero.
Point B represents the spherical nodal surface of Figure 1.
Answer: (2)