The 118 elements of the periodic table represent the fundamental building blocks of all known matter. A chemical element is defined as a pure substance consisting only of atoms that share the same number of protons in their nucleus. This count of protons is the atomic number, which uniquely identifies each element. Scientists recognize 118 distinct elements, from the lightest, Hydrogen (one proton), to the heaviest, Oganesson (118 protons). These elements combine to form every solid, liquid, and gas we encounter, making their study the foundation of chemistry.
The Periodic Table Structure
The Periodic Table is a systematic arrangement that reveals patterns in the physical and chemical behaviors of the 118 elements. Elements are primarily ordered by increasing atomic number, running sequentially from 1 to 118. This ordering demonstrates the periodic law, which describes the recurring pattern of properties as the atomic number increases.
The table is organized into seven horizontal rows, called periods, and vertical columns, known as groups. Each period number corresponds to the number of electron shells, or principal energy levels, that the atoms of those elements possess. For instance, elements in Period 4 all have four occupied electron shells.
The 18 vertical groups are defined by elements that share similar chemical properties due to having the same number of valence electrons. Elements within a group, such as the noble gases in Group 18, tend to behave similarly in reactions. The structure also separates the Lanthanides and Actinides, known as the f-block elements. These two series are typically placed below the main body of the table and fit structurally within periods 6 and 7.
Broad Classification of Elements
The 118 elements are categorized into three broad classes: metals, nonmetals, and metalloids. Metals make up the largest portion of the table, typically found on the left and center. They are generally lustrous, meaning they have a shiny appearance, and are excellent conductors of both heat and electricity. Metals like Iron and Copper are also malleable (easily hammered into thin sheets) and ductile (can be drawn into wires).
Located primarily on the upper right side of the table, nonmetals exhibit properties largely opposite to metals. They are typically dull in appearance and are poor conductors of heat and electricity. Nonmetals are brittle in their solid state and can exist as gases, liquids, or solids at room temperature, such as Oxygen, Bromine, and Carbon.
The metalloids, sometimes called semimetals, occupy a diagonal band between the metals and nonmetals. These elements possess a mix of properties, often having a metallic luster but being brittle like nonmetals. Their most distinctive property is their intermediate electrical conductivity. This semi-conductive behavior makes metalloids like Silicon and Boron indispensable in the electronics industry.
Natural Versus Synthetic Elements
While all 118 elements are recognized, not all exist naturally on Earth. About 98 elements are naturally occurring, with the remaining being synthetic. Synthetic elements are typically created in research laboratories using particle accelerators to force the nuclei of lighter elements to fuse together.
This synthetic group includes the transuranium elements, which are all elements with an atomic number greater than 92 (Uranium). The heaviest elements, such as Oganesson (Element 118), fall into this category. These elements are intensely radioactive and unstable, often decaying into other elements in a matter of milliseconds. Because of their short half-lives, they cannot be produced in large quantities and exist only for scientific study.