The periodic table is a systematic arrangement of chemical elements, organized by increasing atomic number. It groups elements with similar chemical properties into columns (groups) and arranges them in rows (periods) based on their electron configurations.
Developed by Dmitri Mendeleev, it serves as a fundamental tool in chemistry, helping scientists understand element relationships, predict properties, and study trends such as electronegativity, atomic radius, and reactivity.
The periodic table is divided into four blocks based on the electron configuration of elements:
- s-block – Includes Groups 1 & 2 (alkali and alkaline earth metals) and hydrogen & helium.
- p-block – Includes Groups 13 to 18 (nonmetals, metalloids, and noble gases).
- d-block – Contains transition metals (Groups 3 to 12).
- f-block – Includes the lanthanides and actinides, often placed separately at the bottom.
There are some controversies regarding the placement of certain elements, particularly in the d- and f-blocks:
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Group 3 Controversy – There’s debate over whether lanthanum (La) & actinium (Ac) or lutetium (Lu) & lawrencium (Lr) should be placed in Group 3. Different versions of the periodic table use different placements.
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Position of Hydrogen & Helium – Hydrogen is placed in Group 1 (alkali metals) but also has properties similar to Group 17 (halogens), making its placement debatable. Helium is in Group 18 (noble gases), but some argue it should be in Group 2 (alkaline earth metals) based on electron configuration.
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f-block Placement – Some versions of the periodic table integrate lanthanides and actinides directly into the main table, while others keep them separate for better readability.
