2025年3月20日 · Most of the materials that occur on Earth, such as wood, coal, minerals, or air, are mixtures of many different and distinct chemical substances. Each pure chemical …

2025年3月24日 · A chemical reaction is a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are …

Chemical compound, any substance composed of identical molecules consisting of atoms of two or more chemical elements. All the matter in the universe is composed of the atoms of more …

2025年3月26日 · A chemical element is any substance that cannot be decomposed into simpler substances by ordinary chemical processes. Elements are the fundamental materials of which …

chemical formula, any of several kinds of expressions of the composition or structure of chemical compounds. The forms commonly encountered are empirical, molecular, structural, and …

To describe chemical reactions, scientists use chemical equations, which make use of symbols and formulas for elements and compounds. The chemical equation for the reaction between …

2025年3月24日 · The periodic table is a tabular array of the chemical elements organized by atomic number, from the element with the lowest atomic number, hydrogen, to the element …

A chemical element is any substance that cannot be decomposed into simpler substances by ordinary chemical processes. Elements are the fundamental materials of which all matter is …

2025年3月28日 · Salt, also called sodium chloride, mineral substance of great importance to human and animal health, as well as to industry. The mineral form halite, or rock salt, is …

A chemical element is a basic substance. It cannot be broken down into simpler substances. Chemical elements are the building blocks for all matter—that is, everything that takes up …