A chemical element is defined by the number of protons in its atomic nucleus, known as the atomic number. Every atom of a specific element contains the same, unique number of protons, which determines its chemical identity. The periodic table currently organizes 118 confirmed elements, but the number found in nature is significantly smaller. The count of naturally occurring elements on Earth is typically cited as falling between 90 and 94. This ambiguity arises from how scientists classify elements that exist only momentarily as products of radioactive decay.
Defining Elements Found in Nature
The definition of a “natural” element hinges on its longevity and origin. The majority are primordial elements, meaning they were present when the Earth formed and have half-lives long enough to have survived for billions of years. This group includes 80 stable elements (Hydrogen up to Lead) and three long-lived radioactive elements: Bismuth, Thorium, and Uranium. These 83 elements form the foundational set of naturally occurring matter.
The remaining elements are categorized as transient elements, which are short-lived and continuously produced through the natural radioactive decay chains of Uranium and Thorium. The inclusion of these decay products causes the variation in the “natural” element count. Technetium (43), Promethium (61), Astatine (85), and Francium (87) have no stable isotopes and exist on Earth only as these intermediates.
Neptunium (93) and Plutonium (94) are also produced in trace amounts through natural processes, such as neutron capture by Uranium atoms followed by beta decay. When these short-lived decay products are included, the total number of elements found on Earth rises to 94. These elements were initially synthesized in a laboratory before their natural existence was confirmed.
The Synthetic Elements
The total number of elements on the periodic table, 118, contrasts with the 94 found in nature due to synthetic elements. These atoms are created by humans in laboratories, typically using particle accelerators or nuclear reactors. Synthetic elements are generally defined as having atomic numbers greater than 94.
The transuranic elements, those beyond Uranium (atomic number 92), are inherently unstable and decay rapidly. They are created by bombarding a target atom with high-energy particles or other nuclei, forcing them to fuse into a heavier element. Because their longest-lived isotopes have half-lives that are too short to have survived since the Earth’s formation, they are not found in meaningful quantities in nature.
Formation of Natural Elements
The origins of the natural elements trace back to three distinct cosmic events, beginning with the birth of the universe. Big Bang nucleosynthesis, occurring within the first few minutes after the Big Bang, created the lightest elements. This process was responsible for nearly all the Hydrogen and Helium, plus trace amounts of Lithium, that exist today.
Heavier elements were forged later within stars through stellar nucleosynthesis. Inside stars like our Sun, nuclear fusion combines hydrogen into helium. In more massive stars, subsequent fusion stages create elements up to Iron (atomic number 26). The fusion process stops at Iron because fusing it into heavier elements requires more energy than it releases.
The heaviest elements, including Gold, Platinum, and Uranium, required explosive nucleosynthesis for their creation. These atoms are formed specifically in supernovae explosions or the mergers of neutron stars. These catastrophic events involve a rapid flood of neutrons, known as the r-process, which allows nuclei to quickly capture multiple neutrons before they decay, building up the heaviest elements.
The Most Common Elements
The distribution of elements is vastly different between the universe and Earth. The universe is overwhelmingly dominated by the products of the Big Bang, consisting of approximately 75% Hydrogen and 23% Helium by mass. All other elements, which form the planets, stars, and galaxies, make up only about 2% of the universe’s total elemental mass.
In contrast, the Earth’s composition is characterized by denser, rock-forming elements. The overall bulk of the planet is dominated by Iron, Oxygen, and Silicon, with Iron concentrated in the Earth’s core. The Earth’s crust is almost half Oxygen (46.6%) by weight, followed by Silicon (27.7%).
This profound difference is due to the solar system’s formation history. The intense heat from the early Sun and the Earth’s relatively weak gravity caused volatile, light gases like Hydrogen and Helium to escape into space. This process left behind a terrestrial planet composed primarily of the heavier, less volatile elements that condensed to form rock and metal.