Of the 118 elements in the periodic table, the human body relies on just a few key ones. Surprisingly, four elements—oxygen, carbon, hydrogen, and nitrogen—account for about 97% of our body weight, forming the foundation of life's complex systems.
The Periodic Table organizes the 118 known chemical elements by increasing atomic number—the number of protons in an atom's nucleus—which correlates with atomic mass. Elements are arranged left to right and top to bottom.
Horizontal rows, called periods, indicate the number of electron orbitals for elements in that row. Orbitals describe electron positions and wave-like behavior.
Vertical columns, or groups, group elements with the same number of valence electrons in their outermost shell, leading to similar chemical properties. For instance, group 18 elements are noble gases, chemically inert and unreactive.
While dozens of elements are present in the body, four dominate, comprising roughly 97% of body mass: oxygen, carbon, hydrogen, and nitrogen.
Oxygen makes up 65% to 67% of body weight, largely due to water, which constitutes about 60% of our mass. It's vital for energy production, metabolism, and numerous biochemical reactions.
Carbon follows at 18% to 19%, serving as the structural backbone for fats, carbohydrates, and proteins—the building blocks of most life forms on Earth.
Hydrogen, the other half of water (H2O), is abundant atom-for-atom—more than any other element—but contributes only 9% to 10% by mass due to its low atomic weight compared to oxygen (16 times heavier) and carbon (12 times).
Nitrogen accounts for about 3% of body weight and is crucial for amino acids, the units of proteins. It's also a key component of DNA and RNA, enabling genetic storage and cell replication.
