The Periodic Table of Elements is a special tabular overview that lists the basic chemical substances and arranges them based on the specific properties of the individual atom types. The arrangement of the elements does not correspond to an arbitrarily conceived system, but rather reflects atomic phenomena, so that studying the periodic table allows a deep basic understanding of numerous chemical principles and properties to be derived directly from the table.
The periodic table of the elements is a systematic arrangement of all known chemical elements in order of increasing atomic number, that is, the number of protons in the atomic nucleus. This order forms the basis for understanding chemical properties because it reflects the structure of the electron shell. The horizontal rows are called periods, and the vertical columns are called groups. Elements within a group share similar chemical properties because their outermost electron shell is configured in the same way.
At the core of the periodic table’s structure lies the Aufbau principle (also known as the “principle of energetic build-up”). It describes the sequence in which electrons occupy the available energy levels of an atom. The orbitals – s, p, d, and f – are filled in order of increasing energy. Electrons first occupy the lower-energy orbitals before moving to higher ones. This sequence does not strictly follow the numerical shell order but rather the Madelung rule (n + l rule), which determines the energy of each orbital.
This principle gives rise to periodicities - regularly repeating patterns in the elements’ properties. When one electron shell is completely filled and a new period begins, characteristic features such as reactivity, ionization energy, or electronegativity reappear in a systematic way. For example, all elements in Group 1 share a strong tendency to lose one electron, whereas the noble gases at the end of each period are particularly stable and chemically inert.
The structure of the periodic table is therefore not a coincidence but a direct consequence of the quantum-mechanical laws governing the electron configuration of atoms. This makes it one of the most powerful tools in chemistry: it not only organizes known elements but also enables predictions about the properties of those yet to be discovered.
Last update: 2025-10-21
Perma link: https://www.chemlin.org/chemical-elements/periodic-table.php
© 1996 - 2025 ChemLin