Octet rule
From Free net encyclopedia
Image:Octeto.pngThe octet rule is a simple chemical theory that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, similar to the electronic configuration of a noble gas. In simple terms, molecules are more stable when the outer shells of their constituent atoms are empty, full, or have 8 electrons in the outer shell. See electron shells.
The octet rule also states that atoms react generally by gaining, losing, or sharing electrons in order to achieve a complete octet of 8 valance electrons. An octet of electrons results in a very stable electron configuration. This stability is the reason that the noble gases are so unreactive. This combination occurs primarily in two ways, electrovalent bonding and covalent bonding.
Some of the atoms for which the octet rule are most useful are:
However, the exceptions are plenty:
- Hydrogen only needs one additional electron (for a total of two) to have a noble gas structure (that of helium), and lithium needs to lose one (the duet rule of the first shell).
- Any molecule or ion with an odd number of electrons
- Any atom that forms more than four bonds (phosphorus falls under this as well as the rule below)
- The octet rule is inapplicable to atoms in periods greater than 2 because their electron shells can hold more than eight electrons. See hypervalency
- For transition metals an alternative for the octet rule is electron counting.
- Boron is a frequent exception, normally with only 6 electrons in its bonding pairs. Similarly, beryllium normally has 4 electrons in its bonding pairs.
- There are a few special cases in very common substances, notably carbon monoxide and ozone
- Symmetric hydrogen bonds also violate the duet rule.
See also
bn:অষ্টক নিয়ম de:Oktettregel es:Regla del octeto eo:Okopa regulo ko:옥텟 규칙 it:Regola dell'ottetto ja:オクテット則 nn:Oktettregelen uk:Правило Октетів