The members of the family form trihalides ( MX₃) and pentahalides ( MX₅) . The trihalides are sp³ -hybridized with distorted tetrahedral geometry and pyramidal shape while pentahalides are sp³d -hybridized and are trigonal bipyramidal in shape. The trihalides are hydrolyzed by water and ease of hydrolysis decreases when we move down the group. Hence, NCl₃ is easily hydrolyzed but sbcl₃ and BiCl₃ are partly and reversibly hydrolyzed. NF₃ is not hydrolyzed due to lack of vacant d-orbital with nitrogen. PF₃ and PF₅ are also not hydrolyzed because the P – F bond is stronger than P – O covalent bond. The hydrolysis products of the halides are as follows :

NCI₃ + 3H₂O → NH₃ + 3HOCI

PCI₃ + 3H₂O → H₃PO₃ + 3HCI

2AsCI₃ + 3H₂O → As₂O₃ + 6HCI

BiCI₃ + H₂O → BiOCI + 2HCI

Their basic character follows this decreasing order as NI₃ > NBr₃ > NCI₃ > NF₃ . Except NF₃ , the trihalides of nitrogen are unstable and decompose with explosive violence. NF₃ is stable and inert. NCI₃ is highly explosive. Trifluorides and trichlorides of phosphorus and antimony act as Lewis acid. The acid strength decreases down the group. For example, acid strength of tri-chlorides is in the order ; PCI₃ > AsCI₃ > SbCI₃ .

Nitrogen does not form pentahalides due to non-availability of vacant d-orbitals. The pentachloride of phosphorus is not very stable because axial bonds are longer (and hence weaker) than equitorial bond. Hence, PCI₅ decomposes to give PCI₃ and CI₂ ;

PCI₅ PCI₃ + CI₂ .

The unstability of PCI₅ makes it a very good chlorinating agent. All pentahalides act as lewis acids since they can accept a lone pair of electron from halide ion.

Solid PCI₅ is an ionic compound consisting of has [ PCI₄ ]⁺ [ PCI₆ ]^- , [ PCI₄ ]⁺ a tetrahedral structure, while [ PCI₆ ]^- has an octahedral structure.

Since, PCI₅ reacts readily with moisture it is kept in well stoppered bottles.

PI₅does not exist due to large size of I atoms and lesser electronegativity difference between phosphorus and iodine.

Down the group, the tendency to form pentahalides decreases due to inert pair effect. e.g., BiF₅ does not exist.