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  2. Atom - Wikipedia

    en.wikipedia.org/wiki/Atom

    For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. Many elements display multiple valences, or ...

  3. Matter - Wikipedia

    en.wikipedia.org/wiki/Matter

    Because atoms and molecules are said to be matter, it is natural to phrase the definition as: "ordinary matter is anything that is made of the same things that atoms and molecules are made of". (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and ...

  4. Chemical substance - Wikipedia

    en.wikipedia.org/wiki/Chemical_substance

    As of 2019, there are 118 known elements, about 80 of which are stable – that is, they do not change by radioactive decay into other elements. Some elements can occur as more than a single chemical substance . For instance, oxygen exists as both diatomic oxygen (O 2) and ozone (O 3). The majority of elements are classified as metals.

  5. Chemical compound - Wikipedia

    en.wikipedia.org/wiki/Chemical_compound

    A covalent bond, also known as a molecular bond, involves the sharing of electrons between two atoms. Primarily, this type of bond occurs between elements that fall close to each other on the periodic table of elements, yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond.

  6. Chemical element - Wikipedia

    en.wikipedia.org/wiki/Chemical_element

    Atoms of the same element can have different numbers of neutrons in their nuclei, known as isotopes of the element. Two or more atoms can combine to form molecules. Some elements are formed from molecules of identical atoms, e. g. atoms of hydrogen (H) form diatomic molecules (H 2). Chemical compounds are substances made of atoms of different ...

  7. Atomic physics - Wikipedia

    en.wikipedia.org/wiki/Atomic_physics

    Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. Atomic physics typically refers to the study of atomic structure and the interaction between atoms. [1]

  8. List of chemical elements - Wikipedia

    en.wikipedia.org/wiki/List_of_chemical_elements

    A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...

  9. Elementary particle - Wikipedia

    en.wikipedia.org/wiki/Elementary_particle

    Ordinary matter is composed of atoms, themselves once thought to be indivisible elementary particles. The name atom comes from the Ancient Greek word ἄτομος which means indivisible or uncuttable. Despite the theories about atoms that had existed for thousands of years, the