Chemical elements

Chemical elements
Name	Chemical elements
Caption	The Periodic table organizes all known chemical elements.

Chemical elements are the fundamental substances that constitute all ordinary matter in the universe. Each is defined by the number of protons in its atomic nucleus, a value known as the atomic number. These pure substances cannot be broken down into simpler components by ordinary chemical means and serve as the building blocks for every molecule and chemical compound.

Properties and classification

The defining characteristic of any element is its atomic number, which dictates its position on the Periodic table. This table, developed by Dmitri Mendeleev, arranges elements into groups and periods based on recurring trends in their chemical properties. Key classifications include metals, such as iron and copper, which are typically shiny and conductive; nonmetals like oxygen and sulfur; and metalloids, including silicon and germanium, which exhibit intermediate properties. Other important categories are the highly reactive alkali metals, the noble gases known for their inertness, and the lanthanide and actinide series, which include many radioactive elements. Physical and chemical properties, such as atomic radius, ionization energy, and electronegativity, show predictable periodic trends across the table.

Discovery and history

The concept of fundamental elements dates back to ancient philosophies, such as those of Empedocles and Aristotle. The modern scientific understanding began with the work of Robert Boyle and was revolutionized by Antoine Lavoisier, who provided a clear definition and compiled an early list. The 19th century saw the isolation of numerous elements by chemists like Humphry Davy, who used electrolysis to discover potassium and sodium. The development of the Periodic table by Dmitri Mendeleev allowed for the prediction of undiscovered elements, such as gallium and germanium. The 20th century brought the discovery of radioactivity by Marie Curie and the subsequent synthesis of transuranium elements like plutonium at facilities such as Lawrence Berkeley National Laboratory.

Abundance and occurrence

The abundance of elements varies enormously across the universe, Earth, and the human body. In the cosmos, hydrogen and helium, formed during the Big Bang and in stellar nucleosynthesis, are by far the most common. On Earth, the Earth's crust is dominated by oxygen and silicon, while the Earth's core is primarily composed of iron and nickel. Elements are found in various forms, from native metals like gold and copper to complex minerals within ores. The distribution is a result of planetary formation processes and geochemical cycles. In biological systems, carbon, hydrogen, oxygen, and nitrogen are the primary constituents of biomolecules.

Synthesis and production

While many elements occur naturally, others must be synthesized. The extraction of metals often involves mining ores and processes like smelting, as seen in iron production in a blast furnace, or electrolysis, used for aluminum via the Hall–Héroult process. Synthetic elements, primarily those beyond uranium on the periodic table, are created artificially using particle accelerators like the Joint Institute for Nuclear Research in Dubna or through nuclear reactors, as with plutonium production. These methods involve bombarding target nuclei with particles or neutrons to induce nuclear transmutation.

Applications and uses

Elements and their compounds are indispensable to modern technology and industry. Silicon is the foundation of the semiconductor industry and integrated circuits. Iron, alloyed with carbon to make steel, is critical for construction and infrastructure. Precious metals like platinum and palladium serve as catalysts in automotive catalytic converters and chemical manufacturing. Uranium and plutonium are fuels for nuclear power generation, while lithium is essential for batteries in devices and electric vehicles. Tungsten is used for filaments in light bulbs due to its high melting point.

Biological role and toxicity

Many elements are essential for life. Carbon, hydrogen, oxygen, and nitrogen form the backbone of DNA and proteins. Calcium is vital for bone structure, iron is central to hemoglobin in red blood cells, and trace amounts of elements like iodine and selenium are crucial for hormone function. However, elements can also be toxic. Heavy metals such as lead, mercury, and cadmium are potent neurotoxins that can cause severe health issues, as historically seen with Minamata disease. Even essential elements like iron or copper can be harmful in excessive amounts, leading to conditions such as hemochromatosis.

Category:Chemistry