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  2. Oxygen - Wikipedia

    en.wikipedia.org/wiki/Oxygen

    Oxygen is a chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table , a highly reactive nonmetal , and a potent oxidizing agent that readily forms oxides with most elements as well as with other compounds .

  3. 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 ...

  4. Chemical element - Wikipedia

    en.wikipedia.org/wiki/Chemical_element

    The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus. 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.

  5. List of elements by atomic properties - Wikipedia

    en.wikipedia.org/wiki/List_of_elements_by_atomic...

    This is a list of chemical elements and their atomic properties, ordered by atomic number (Z).. Since valence electrons are not clearly defined for the d-block and f-block elements, there not being a clear point at which further ionisation becomes unprofitable, a purely formal definition as number of electrons in the outermost shell has been used.

  6. Allotropes of oxygen - Wikipedia

    en.wikipedia.org/wiki/Allotropes_of_oxygen

    Atomic oxygen, denoted O or O 1, is very reactive, as the individual atoms of oxygen tend to quickly bond with nearby molecules. Its lowest-energy electronic state is a spin triplet, designated by the term symbol 3 P. On Earth's surface, it exists naturally for a very short time.

  7. Chemical symbol - Wikipedia

    en.wikipedia.org/wiki/Chemical_symbol

    Symbol Name Atomic number Origin of symbol Ac: Actinium: 89: From Greek aktinos. Name restricted at one time to 227 Ac, an isotope of actinium. This named isotope later became the official name for element 89. AcA: Actinium A: 84: From actinium and A. Placeholder name given at one time to 215 Po, an isotope of polonium identified in the decay ...

  8. Period 2 element - Wikipedia

    en.wikipedia.org/wiki/Period_2_element

    Oxygen is the chemical element with atomic number 8, occurring mostly as 16 O, but also 17 O and 18 O. Oxygen is the third-most common element by mass in the universe (although there are more carbon atoms, each carbon atom is lighter). It is highly electronegative and non-metallic, usually diatomic, gas down to very low temperatures.

  9. Atomic number - Wikipedia

    en.wikipedia.org/wiki/Atomic_number

    The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (n p) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ...