How would you best explain the octet rule?
A For many elements, acquiring eight electrons in the valence electron shell allows the element to form chemical bonds with other elements.
B When some elements form chemical bonds, the elements accept, share, or donate electrons so that their valence electron shell contains eight electrons.
C An element that has a minimum of eight electrons in its innermost electron shell will not form a chemical bond with other elements.
D Elements randomly gain electrons from, or lose electrons to, other elements until all of the elements have eight electrons.
The correct answer and explanation is:
The correct answer is B: When some elements form chemical bonds, the elements accept, share, or donate electrons so that their valence electron shell contains eight electrons.
The octet rule is a fundamental concept in chemistry, particularly when explaining how atoms interact to form molecules. It states that most elements tend to form chemical bonds in such a way that each atom involved achieves a stable electron configuration, which often means having eight electrons in their valence shell (the outermost shell). This is because a full valence shell provides a more stable configuration for the atom, similar to that of the noble gases (such as helium, neon, or argon), which naturally have full valence shells and are chemically inert.
For atoms to achieve this stability, they engage in chemical bonding. There are three main types of bonding that help atoms reach an octet:
- Ionic bonds: In this type of bond, atoms transfer electrons. One atom donates an electron to achieve a full outer shell, while the other atom accepts the electron to complete its valence shell. A good example is sodium (Na) and chlorine (Cl), where sodium donates an electron to chlorine, forming Na+ and Cl-, which then attract each other due to opposite charges.
- Covalent bonds: Atoms can share electrons to complete their octet. This typically happens between nonmetals, such as in the case of two oxygen atoms forming O2, where they share electrons equally to each achieve a full shell.
- Metallic bonds: In metals, electrons are not shared or transferred between specific atoms, but instead form a “sea of electrons” that move freely between the metal atoms, contributing to properties like electrical conductivity.
By achieving a stable configuration of eight valence electrons, atoms become less reactive and more stable. However, there are exceptions to the rule, particularly with elements like hydrogen, helium, and other small atoms, which may require fewer than eight electrons to achieve stability.