Valence electrons is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
The presence of valence electrons can determine the elements chemical properties, such as its valence—whether it may bond with other elements and, if so, how readily and with how many. In this way, a given element's reactivity is highly dependent upon its electronic configuration. For a main group element, a valence electron can exist only in the outermost electron shell; in a transition metal, a valence electron can also be in an inner shell.
An atom with a closed shell of valence electrons (corresponding to an electron configuration s2p6 for main group elements) tends to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive due to the relatively low energy to remove the extra valence electrons to form a positive ion. An atom with one or two electrons less than a closed shell is reactive due to its tendency either to gain the missing valence electrons and form a negative ion, or else to share valence electrons and form a covalent bond.
Similar to a core electron, a valence electron has the ability to absorb or release energy in the form of a photon. An energy gain can trigger the electron to move (jump) to an outer shell; this is known as atomic excitation. Or the electron can even break free from its associated atom's shell; this is ionization to form a positive ion. When an electron loses energy (thereby causing a photon to be emitted), then it can move to an inner shell which is not fully occupied.
When forming ions, elements typically gain or lose the minimum number of electrons necessary to achieve a full octet. For example, fluorine has seven valence electrons, so it is most likely to gain one electron to form an ion with a 1- charge.
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A change will only occur one time in unidirectional.
Because
Cyclic : Cyclic compounds are chemical compounds having a basic non-linear structure. In other words, these are ring structures. One or more series of atoms in the compound is connected to form a ring structure.
Periodic : The periodic table of chemical elements, often called the periodic table, organizes all discovered chemical elements in rows (called periods) and columns (called groups) according to increasing atomic number.
Unidirectional : compound is operating or moving in one direction only and it does not move in other direction.
Bidirectional : Capable of reacting or functioning in two, usually opposite, directions.
Thus, A change will only occur one time in unidirectional.
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Explanation:
Bacteria play a key role in the nitrogen cycle.
Nitrogen-fixing microorganisms capture atmospheric nitrogen by converting it to ammonia— NH3start text, N, H, end text, start subscript, 3, end subscript—which can be taken up by plants and used to make organic molecules.
Answer:
letter A.
Explanation:
the rate of a chemical reaction can be raised by increasing the surface area of a solid reactant. this is done by cutting the substance into small pieces, or by grinding it into a powder.if the surface area of a reactant is inceased: more particles are exposed to the other reactant.
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