Question

Guys can you help me with these electronic configuration notation

Answer 1

All 4 period elements have configuration \[ns^x(n-1)d^y\] and so are d-block elements

Lactinides ans Actinides have configuration \[[core]ns^x(n-1)d^y(n-2)f^z\] and so are f-block elements.

I can't seem to understand the notation ): any kind soul can help me?

Answer 2

Not all 4 period elements have the same E.C.
An element is placed in a block, which corresponds to the subshell in which the differentiating electron(the last electron to enter the element) enters while assigning the E.C.

Lanthanides and Actinides are the only f-block elements.
Transitional elements are the d-block elements.
Group 1 & 2: s-block
Group 13-18: p-block Exception: He (It hasn't found the perfect place yet. According to it's E.C it should be in s-block. But due to it's atomicity it's placed above p-block's)