Question #3249d

1 Answer
Apr 3, 2016

Elements form compounds in order to become stable and fill up their outer shell of electrons.


Atoms have orbitals of negative electrons around the positive nucleus. The orbitals form shells, each of which can accommodate a certain number of electrons.

For non-transition metals (including lanthanides and actinides), the first shell can hold 2 electrons, and after that they hold 8.

Various quantum mechanical reasons dictate that the atom wants to fill up its outer or valence shell so that it is stable and doesn't react any more. It does this by forming a compound, through reacting with another atom or atoms.

Reactions are when electrons are moved around in different ways to satisfy each atom and form bonds, so all the valence shells are full and nothing can react any more, without applying a very high energy to it.

Bonding mostly happens in one of three ways to form a compound. Covalent bonding is where non-metal atoms share electrons so both shells are full. Ionic bonding is where a metal gives electrons to a non-metal, making both into charged molecules, so they stick together like two ends of a magnet. Metallic bonding happens with metals, where extra electrons form a sea of negative charge and the positive metal nuclei are attracted to it.

Some elements don't form compounds because they naturally have full outer shells. These are the noble gases, such as helium, neon, xenon and krypton. They have no need to bond, although by applying large amounts of energy to them you can force them to bond.