Bonding and the Resulting Properties of Solids

Atoms bind to each other through the interaction of their outermost electrons. These electrons, otherwise referred to as valence electrons, interact through the formation of bonding and anti-bonding states. The resulting states are referred to as molecular orbitals (MOs). Those in unbound atoms are referred to as atomic orbitals (AOs). 

No interaction between 4s states when atoms are far apart. 4s state remain unaffected. c in 4s(t/ Formation of bonding (4sa) and anti-bonding states (4so ) during the interaction of two atoms. 

The bond type formed can fall into one of three different categories, these being  

Although core level states (the inner electron stationary states) do not partake in bonding, their energies can also be influenced, albeit by a small amount. This primarily arises from variation in the effective nuclear charge felt by the core electrons as valence electrons are added or removed from the atom during the course of bond formation. 

---