Chemical composition of elements
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Chemical Composition of Elements in the Universe
The chemical composition of elements in the universe is highly uneven. Hydrogen is the most abundant element, making up over 90% of the atoms and about 75% of the mass of the universe. Helium is the next most common, with all other elements combined contributing only a small fraction to the total mass. The composition of the universe changes over time as hydrogen is converted into helium and heavier elements through nuclear processes in stars. This ongoing transformation increases the proportion of heavier elements relative to hydrogen as the universe ages .
Formation and Distribution of Elements
Elements are formed through various nuclear processes in stars, including hydrogen burning, helium burning, and several other processes (such as the s-process and r-process). Most heavy elements are believed to have originated in supernovae or the hot interiors of stars. The distribution of elements is not uniform across different celestial bodies. For example, lunar rocks are enriched in refractory elements like chromium and titanium, while being poor in volatile elements and noble metals. Meteorites, especially carbonaceous chondrites, are among the most primitive objects and have elemental abundances similar to those found in the solar chromosphere .
Chemical Composition of the Earth and Other Planets
The Earth's crust is primarily composed of oxygen (about 47% by weight), silicon (28%), and aluminum (8%). Along with iron, calcium, sodium, potassium, and magnesium, these elements make up about 99% of the crust. Many elements essential to human civilization, such as tin, copper, and gold, are actually among the rarest in the crust and are concentrated in ore bodies through geological processes. On Mars, the soil contains significant amounts of iron, silicon, calcium, aluminum, and titanium, but no organic compounds have been detected .
Essential Elements for Life
At least 24 elements are considered essential for living organisms. The most abundant in the human body are hydrogen, oxygen, carbon, and nitrogen. Other important elements include calcium, phosphorus, chlorine, potassium, sulfur, sodium, and magnesium. Trace elements like iron, copper, zinc, and iodine also play crucial roles in biological processes .
Isotopic Composition and Atomic Structure
Each element is defined by its number of protons (atomic number, Z), but elements can have different numbers of neutrons, resulting in isotopes. The mass number (A) is the sum of protons and neutrons. Isotopic abundances can vary in terrestrial materials, and the International Union of Pure and Applied Chemistry (IUPAC) regularly updates the evaluated data on isotopic compositions to reflect the best available measurements and known variations .
Elements as Substances and Constituents
The concept of a chemical element has a dual nature. Elements can be considered both as simple substances (in their pure form) and as basic constituents of compounds. When elements form compounds, their identity as a substance disappears, but they remain as constituents within the compound. This duality is important for understanding chemical reactions and the persistence of elements in different forms of matter 63.
Chemical Differentiation in the Earth
The Earth's crust and mantle show distinct chemical compositions due to processes like melting and differentiation. The continental crust is enriched in highly incompatible elements, while the oceanic crust contains moderately incompatible elements. These patterns are explained by models of crust formation and mantle differentiation, which also account for anomalies in the distribution of certain elements like niobium, tantalum, and lead .
Modern Approaches to Elemental Composition Analysis
Recent advances in artificial intelligence, such as deep learning models, have enabled the prediction of material properties directly from elemental composition. These models can automatically capture the interactions and similarities between elements, allowing for rapid screening and discovery of new materials without extensive manual input .
Conclusion
The chemical composition of elements is fundamental to understanding the structure and evolution of the universe, the Earth, and living organisms. Elements are distributed unevenly, formed through complex stellar processes, and play diverse roles in both geology and biology. Advances in measurement and computational techniques continue to enhance our understanding of elemental composition and its implications across scientific disciplines 2475.
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