SUBSHELL BLOCK THAT BEGINS TO FILL AFTER 4S2
The subshell that begins to fill after the 4s2 subshell is the 3d subshell. This is because in the filling order of electron shells and subshells, the 4s subshell is filled before the 3d subshell.
To understand why this is the case, we need to look at the electronic configuration of atoms. The electronic configuration describes the distribution of electrons in an atom's orbitals.
In the case of the 4s2 subshell, it refers to the 4th energy level (or shell) and the s-type subshell with a maximum capacity of 2 electrons. The 4s subshell fills before the 3d subshell because of the Aufbau principle, which states that electrons fill lower energy levels before higher energy levels.
So, after the 4s2 subshell is filled, the 3d subshell begins to fill. The 3d subshell is part of the 3rd energy level and can hold a total of 10 electrons.
To determine the electronic configuration of an element, you can refer to the periodic table. Find the element's atomic number, which tells you the number of protons or electrons in the atom. Then, you can fill up the electron orbitals according to the Aufbau principle and electron capacity rules.
For example, let's take the element titanium (Ti) with an atomic number of 22. The electronic configuration of titanium would be 1s2 2s2 2p6 3s2 3p6 4s2 3d2. After the 4s2 subshell is filled, the 3d subshell begins to fill with 2 electrons.
I hope this explanation helps! Let me know if you have any more questions.