The periodic table is one of the most important tools in chemistry. It organizes all known elements by their atomic number and reveals patterns in their properties. Elements are arranged in rows called periods and columns called groups, with similar properties appearing in regular intervals.
Each element has a unique atomic structure that determines its chemical properties. Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in orbital shells. The number of protons, called the atomic number, defines the element's identity and determines its position in the periodic table.
The periodic table reveals predictable patterns in element properties called periodic trends. One important trend is atomic radius, which generally decreases across a period from left to right. This happens because as we add protons to the nucleus, the increased positive charge pulls electrons closer, making atoms smaller despite having more electrons.
Elements in the same column of the periodic table form groups or families with similar properties. This happens because they have the same number of valence electrons in their outer shell. For example, alkali metals have one valence electron, halogens have seven, and noble gases have eight, making them very stable.