Скачать или смотреть How to find the PERIOD, BLOCK and GROUP of an Element in Periodic Table |

To determine the period, block, and group of an element in the periodic table, you generally need its atomic number or electron configuration. Here’s a simple method you can use for any element:
The period number = number of electron shells (energy levels).

👉 Period: Look at the highest principal quantum number (n) in the electron configuration.
Example:
Element: Chlorine (Cl), Z = 17
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁵
Highest n = 3 → Period 3
Block: The block is based on the subshell being filled last:
If the last electron enters s-orbital → s-block
If the last electron enters p-orbital → p-block
If the last electron enters d-orbital → d-block
If the last electron enters f-orbital → f-block
Example:
Cl ends in 3p⁵ → p-block
Group: Rules depend on whether it's s-block, p-block, or d-block.
A) s-block elements (Groups 1–2)
Group number = number of electrons in the outermost s orbital
ns¹ → Group 1
ns² → Group 2
B) p-block elements (Groups 13–18)
Group number = 10 + (electrons in ns and np outer orbitals)
Example (Chlorine):
3s² 3p⁵ → electrons in outer shell = 2 + 5 = 7
Group = 10 + 7 = Group 17
C) d-block elements (transition metals, Groups 3–12)
Group number = electrons in (n-1)d + ns
Example: Fe, Z = 26
Electron configuration: [Ar] 3d⁶ 4s²
Group = 6 + 2 = Group 8
D) f-block elements
They belong to Lanthanides or Actinides.

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