A chemical element is a fundamental substance that cannot be broken down into simpler components. Each element is defined by the number of protons in its atoms, known as its atomic number. These building blocks of matter are organized in the Periodic Table, arranged by increasing atomic number and grouped by similar characteristics. The table lists 118 known elements, both naturally occurring and laboratory-created.
How We Define Common Elements
The term “common” for elements varies by context. Commonality can refer to an element’s abundance, meaning its quantity in an environment like the universe or Earth’s crust. It also considers ubiquity or relevance, indicating how frequently an element is encountered in daily life or its widespread importance. An element common in one setting, like space, might not be as common in human-made products, showing commonality is context-dependent.
Elements in the Universe
The universe’s composition is dominated by the lightest elements, a result of the Big Bang. Hydrogen accounts for approximately 75% of normal matter, while helium makes up about 24%. These two elements formed in the early cosmos.
Heavier elements, beyond hydrogen and helium, were forged later within stars through nucleosynthesis. Stars fuse lighter elements, such as hydrogen and helium, into progressively heavier ones like carbon and oxygen in their cores. Elements heavier than iron are created in explosive events like supernovae or during the collision of neutron stars.
Elements on Earth
Earth’s elemental composition differs significantly from that of the universe. Oxygen is the most abundant element in Earth’s crust, making up about 46% of its mass, primarily forming minerals. Silicon is the second most common, comprising around 28% of the crust, and is a key component of rocks and sand. Other notable elements in the crust include aluminum (around 8%), iron (about 5%), calcium (around 4%), sodium (approximately 2.4%), and magnesium (around 2.3%).
Earth’s atmosphere is predominantly composed of nitrogen, which makes up about 78% of its volume. Oxygen constitutes approximately 21% of the atmosphere and is essential for respiration and combustion. Argon is present in smaller amounts, around 0.93%, while carbon dioxide, although only about 0.04%, plays an important role in regulating Earth’s climate.
Oceans are primarily water, with oxygen making up about 86% and hydrogen around 11% by mass. Dissolved salts contribute other common elements, with chlorine (around 1.9%) and sodium (about 1.1%) being the most prevalent. Magnesium is also found in significant quantities in seawater, around 0.14%.
Within living organisms, a few elements form the foundation of life. Oxygen is the most abundant element by mass in the human body, accounting for about 65%. Carbon makes up around 18.5% of body mass, followed by hydrogen at approximately 9.5%. Nitrogen (about 2.6%), calcium (around 1.3%), and phosphorus (about 0.6%) are also found in substantial amounts. Sulfur, potassium, sodium, and chlorine are present in smaller but significant quantities.
Elements in Everyday Life
Many elements are integral to daily life due to their properties and availability. Iron is widely used in construction and manufacturing, forming steel for tools, structures, and vehicles. Copper’s excellent electrical conductivity makes it a choice for electrical wiring and electronic components. Aluminum, known for its lightweight nature and corrosion resistance, is found in beverage cans, food foil, and aircraft parts.
Carbon is a versatile element, forming the basis of organic matter, plastics, and fuels, and is found in various forms like diamonds and graphite. Oxygen is essential for human respiration and also plays a role in combustion processes and water purification. Nitrogen, a major component of air, is used in fertilizers and food packaging. Sodium and chlorine combine to form table salt, a common food additive.
Calcium is a primary component of bones and teeth and is used in cement and construction materials. Hydrogen, while abundant in water, has potential as a clean energy source in fuel cells. Silicon is a key element in the digital age, used for computer chips and electronic devices.