The periodic table is a tabular arrangement of chemical elements based on their atomic number, electron configuration, and recurring chemical properties. It includes all known chemical elements, represented by unique symbols, arranged in ascending order of atomic number. The table is organized into rows called periods, which correspond to different energy levels or shells in an atom.
The periodic table is divided into main groups (1 to 18) and transition metals, including elements like alkali metals, alkaline earth metals, halogens, and noble gases. Blocks are also classified based on the subshell in which the last electron resides, such as s-block, p-block, d-block, and f-block.
Periodic trends are displayed in the table, such as the gradual increase or decrease of properties across a period or down a group. Common trends include atomic size, ionization energy, and electronegativity.
Noble gases, group 18 elements, are chemically inert and have a full outer electron shell, characterized by their stability and lack of reactivity. Lanthanides and actinides are located at the bottom of the periodic table and are often shown separately due to their similar electron configurations.
The periodic table was initially proposed by Dmitri Mendeleev in 1869, who arranged elements based on their atomic mass and predicted the properties of undiscovered elements. It serves as a fundamental tool in chemistry, providing a systematic way to understand the relationships and properties of different elements.
Why element arranged in table?
The modern periodic table, created by Dmitri Mendeleev in 1869, is a result of his efforts to organize chemical elements in a way that was not always apparent. Mendeleev began collecting and sorting known properties of elements while traveling by train, noticing that groups of elements exhibited similar properties but also found many exceptions to the emerging patterns. He tried to alter measured property values to better fit the patterns and predicted certain elements to exist that didn't at the time. Despite facing skepticism and taking years to gain international acceptance, Mendeleev's patterns became undisputed once newly-discovered elements matched his predictions. Some of his "fudged" properties were later recalculated and found to be closer to his predictions.
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