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.
Answer: The ocean plays a key role in this vital cycle of water. The ocean holds 97% of the total water on the planet; 78% of global precipitation occurs over the ocean, and it is the source of 86% of global evaporation. ... Water evaporates from the surface of the ocean, mostly in warm, cloud-free subtropical seas.
Explanation:
Hope this helps!
C.
It is the only thing that is making a new thing, and not breaking or taking apart something that is already there.
Responder:
2H2 + O2 → 2H2O
CaO + H2O → Ca (OH) 2
Fe + S → FeS
H2SO3 → SO2 + H2O
CaCO3 → CaO + CO2
Explicación:
2H2 + O2 → 2H2O
2 moléculas de hidrógeno gaseoso reaccionan con oxigente para producir 2 moléculas de agua
CaO + H2O → Ca (OH) 2
El óxido de calcio reacciona con el agua para producir hidróxido de calcio.
Fe + S → FeS
El hierro reacciona con el azufre para producir sulfuro de hierro.
H2SO3 → SO2 + H2O
Por descomposición, el ácido sulfuroso se descompone para producir dióxido de azufre y agua.
CaCO3 → CaO + CO2
El carbonato de calcio se descompone para producir óxido de calcio y dióxido de carbono.
