Arrange $s, p$ and $d$ subshells of a shell in the increasing order of effective nuclear charge ( $\left.Z_{\text {eff }}\right)$ experienced by the electron present in them.
$s$-orbital is spherical in shape, it shields the electrons from the nucleus more effectively than $p$ - orbital which in turn shields more effectively than $d$-orbital.
Therefore, the effective nuclear charge $\left(Z_{\text {eff }}\right)$ experienced by electrons present in them is $d
Show the distribution of electrons in oxygen atom (atomic number 8) using orbital diagram.
From the orbital diagram, it is seen that there are two unpaired electrons.
Nickel atom can lose two electrons to form $\mathrm{Ni}^{2+}$ ion. The atomic number of nickel is 28 . From which orbital will nickel lose two electrons?
${ }_{28} \mathrm{Ni}=1 s^2, 2 s^2, 2 p^6, 3 s^2, 3 p^6, 3 d^8, 4 s^2$; Nickel will lose 2 electrons from $4 s$ (outermost shell) to form $\mathrm{Ni}^{2+}$ ion.
Hence, $${ }_{28} \mathrm{Ni}^{2+}=1 s^2, 2 s^2, 2 p^6, 3 s^2, 3 p^6, 3 d^8, 4 s^0$$
$$\begin{aligned} &\text { Which of the following orbitals are degenerate? }\\ &3 d_{x y}, 4 d_{x y}, 3 d_{z^2}, 3 d_{y z}, 4 d_{y z}, 4 d_{z^2} \end{aligned}$$
The orbitals which belongs to same subshell and same shell are called degenerate orbitals. $\left(3 d_{x y}, 3 d_{z^2}, 3 d_{y z}\right)$ and $\left(4 d_{x y}, 4 d_{y z}, 4 d_{z^2}\right)$ are the two sets of degenerate orbitals.
Calculate the total number of angular nodes and radical nodes present in $3 p$ orbital.
For $3 p$-orbital, principal quantum number, $n=3$ and azimuthal quantum number $l=1$
Number of angular nodes $=l=1$
Number of radial nodes $=n-l-1=3-1-1=1$