Why do the d and f block elements have only 2 valence electrons?
The d and f block elements have only 2 valence electrons because valence electrons are the outermost electrons of an atom, and they are involved in the formation of chemical bonds.
To explain why the d and f block elements have 2 valence electrons, we need to understand the electron configuration of atoms.
In the periodic table, each row represents a period. The first period has 2 elements (hydrogen and helium), the second period has 8 elements, the third period has 8 elements, and so on. The elements in the first two periods (1s and 2s) have only 2 valence electrons.
However, the valence electron configuration for the d block elements (transition metals) is slightly different. The d block elements fill the energy levels between the 4th and 5th periods. For example, the 3d block elements fill the energy levels between the 4s and 4p orbitals, while the 4d block elements fill the energy levels between the 5s and 5p orbitals.
To determine the number of valence electrons, we need to look at the highest energy level that contains electrons. For the d block elements, this is the (n-1)d orbitals. These orbitals can hold a maximum of 10 electrons. However, since the valence electrons are the outermost electrons, they are located in the ns orbitals, not the (n-1)d orbitals.
For the f block elements (lanthanides and actinides), the valence electrons are located in the (n-2)f orbitals. These orbitals can hold a maximum of 14 electrons. Again, the valence electrons are located in the outermost energy level, which is the ns orbitals.
Therefore, the d and f block elements have only 2 valence electrons because the valence electrons are in the ns orbitals, while the (n-1)d or (n-2)f orbitals are filled with other electrons.