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  1. Chemical compound | Definition, Examples, & Types | Britannica

    Dec 16, 2025 · All the matter in the universe is composed of the atoms of more than 100 different chemical elements, which are found both in pure form and combined in chemical compounds.

  2. Chemistry | Definition, Topics, Types, History, & Facts | Britannica

    Dec 26, 2025 · Cooking, fermentation, glass making, and metallurgy are all chemical processes that date from the beginnings of civilization. Today, vinyl, Teflon, liquid crystals, semiconductors, and …

  3. Chemical reaction | Definition, Equations, Examples, & Types - Britannica

    Nov 30, 2025 · Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

  4. Chemical Definition & Meaning | Britannica Dictionary

    CHEMICAL meaning: 1 : of or relating to chemistry; 2 : working by means of chemicals

  5. Chemical element | Definition, Origins, Distribution, & Facts - Britannica

    Nov 29, 2025 · 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 …

  6. Chemical formula | Definition, Types, Examples, & Facts | Britannica

    Nov 1, 2025 · 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 …

  7. Chemical energy | Definition & Facts | Britannica

    Chemical reactions differ from physical changes, which include changes of state, such as ice melting to water and water evaporating to vapor. If a physical change occurs, the physical properties of a …

  8. chemical reaction - Students | Britannica Kids | Homework Help

    The substances in a chemical reaction may be chemical elements, molecules, or compounds. The substances present at the start of a chemical reaction are called the reactants; the substances …

  9. The Horrifying History of Gas Warfare | Britannica

    But Haber was willing to pervert this chemical genius to help Germany win the war. And he set out to craft deadlier chemical weapons, leading a group of scientists the German military ghoulishly called …

  10. Periodic table | Definition, Elements, Names, Symbols, Groups, Charges ...

    Dec 22, 2025 · Periodic table, in chemistry, is an organized array of all the chemical elements in order of increasing atomic number. When the elements are thus arranged, there is a recurring pattern in …