The Lewis structure for BeH₂ is as follows:
H: Be: H
There is no lone pair at the central atom (Be) and there are two bond pairs. Hence, BeH₂ is of the type AB₂. It has a linear structure.
\(\nrightarrow \nleftarrow \)
H------Be-----H
Dipole moments of each H - Be bond are equal and are in opposite directions. Therefore, they nullify each other. Hence, BeH₂ has a zero dipole moment.

Hybridisation: It is the phenomenon of intermixing of atomic orbitals of slightly different energies to form new hybrid orbitals of equivalent energy. Formation of water. In water (H₂0), the atomic number of oxygen is 8 and its orbitals electronic configuration is 1s² 2s² \({ 2 }_{ x }^{ 2 }{ \ 2p }_{ y }^{ 1 }{ \ 2p }_{ z }^{ 1 }\) . The oxygen atom is also Sp³ hybridised. However, in this case, the two orbitals with one electron each (half filled) are involved in overlap with the hydrogen orbitals.

When a cheroical bond is fonned by the complete transfer of electrons from one atom to another, so as to complete their outermost shell and therefore, aquire the stable noble gas configuration, the bond fanned is called ionic bond or electrovalent bond.
\(\underset { 2,8,1 }{ Na } \longrightarrow \underset { 2,8 }{ Na } ^{ + }+{ e }^{ - }\)
\(CI \ + \ { e }^{ - }\longrightarrow \left[ \underset { 2,8,8 }{ CI } \right] ^{ - }\)
\(\overset { 2,8,7 }{ Na } +{ CI }^{ - }\longrightarrow \left[ { Na }^{ + } \right] \left[ CI \right] ^{ - } \)

Formation of magnesium oxide (MgO)

\({ NH }_{ 4 }^{ + }\) ion contains covalent and dative bonds. (It is formed by donation of lone pair of electrons on N in NH₃ to H⁺ ion). \({ NO }_{ 3 }^{ - }\) ion also contains covalent and davite bonds.
Bond between \({ NH }_{ 4 }^{ + }\) and \({ NO }_{ 3 }^{ - }\) ions is ionis.
N of \({ NH }_{ 4 }^{ + }\) ion is sp³ hydridised and is tetrahedral.
N of \({ NO }_{ 3 }^{ - }\) ion is sp² hybridised and is planar.

(a) same bond order and bond length.
(b) Same bond order and bond length.