The strong interaction between two or more adjacent atoms (or ions) is called chemical bond. Chemical bonds are mainly divided into ionic bonds, valence bonds and metal bonds.
1, the ionic bond is formed by electrostatic attraction between right positive and negative ions. The positive and negative ions are spherical or nearly spherical, and the charges are distributed spherically symmetrically, so the ionic bond can act electrostatically in all directions, so there is no directionality.
2. One ion can attract multiple ions with opposite charges to form bonds at the same time. Although in ionic crystals, one ion can only directly interact with several ions with opposite charges (for example, Na+ in NaCl can directly interact with six Cl-), this is due to space factors. At a long distance, there is also a weak effect, so there is no saturation.
The valence bond formation of 1 and * * * is the atomic orbital overlap of bonding electrons. To stabilize the valence bond of * * *, the overlapping part must be the largest. Since all tracks except the S track extend in a certain direction, the bonds formed by other tracks can only overlap in a certain direction except σ bonds of s-s (such as H2) overlap in any direction.
2. Old theory: the condition for the formation of valence bond is that there must be a single electron in the atom and the spin direction must be opposite. Because a single electron of an atom can only be paired with another single electron, the valence bond of * * * is saturated. For example, after atoms form HCl molecules with Cl atoms, they cannot form HCl2 with another Cl.
New theory:
* * * When valence bonds are formed, the atomic orbitals of bonding electrons overlap and split, and the bonding electrons are filled into the lower energy orbitals, that is, bonding orbitals. If other atoms participate in bonding, the electrons provided by them will be filled into the anti-bonding orbit with higher energy, and the formed molecules will be unstable.