Due to its small size and similar charge/mass ratio, boron differs from other group 13 members, but it resembles closely with silicon, the second element of group 14 to exhibit diagonal relationship. Some important similarities between boron and silicon are given below,

(1) Both boron and silicon are typical non-metals, having high m.pt. b.pt nearly same densities (B=2.35gml^–1 S=2.34 g//ml). low atomic volumes and bad conductor of current. However both are used as semiconductors.

(2) Both of them do not form cation and form only covalent compounds.

(3) Both exists in amorphous and crystalline state and exhibit allotropy.

(4) Both possess closer electronegativity values (B=2.0; Si=1.8).

(5) Both form numerous volatile hydrides which spontaneously catch fire on exposure to air and are easily hydrolysed.

(6) The chlorides of both are liquid, fume in most air and readily hydrolysed by water.

BCl₃ + 3H₂O → B(OH)₃ + 3HCl

SiCl₄ + H₂O → Si(OH)₄ + 4HCl

(7) Both form weak acids like H₃BO₃ and H₂SiO₃.

(8) Both form binary compounds with several metals to give borides and silicide. These borides and silicide react with H₃PO₄ to give mixture of boranes and silanes.

3Mg+2B → Mg₃B₂; Mg₃B₂ + H₃PO₄ → Mixture of boranes ^{(Magnesium boride)}

2Mg + Si → Mg₂Si ; Mg₂Si + H₃PO₄ → Mixture of silanes ^{(magnesium silicide)}

(9) The carbides of both Boron and silicon (B₄C and SiC) are very hard and used as abrasive.

(10) Oxides of both are acidic and can be reduced by limited amount of Mg In excess of Mg boride and silicide are formed.

B₂O₃ + 3Mg → 3MgO + 2B ; SiO₂ + 2Mg → 2MgO + Si

(11) Both the metals and their oxides are readily soluble in alkalies.

2B + 6NaOH → 2Na₃BO₃ + 3H₂ ­^(borate)

Si + 2NaOH + H₂O → Na₂SiO₃ + 2H₂ ­^(silicate)

B₂O₃ + 6NaOH → 2Na₃BO₃ + 3H₂O

SiO₂ + 2NaOH → Na₂SiO₃ + H₂O

Both borates and silicates have tetrahedral structural units and respectively. Boro silicates are known in which boron replaces silicon in the three dimensional lattice. Boron can however form planar BO₃ units.

(12) Acids of both these elements form volatile esters on heating with alcohol in presence of conc. H₂SO₄.

B(OH)₃ + 3ROH → B(OR)₃ + 3H₂O

Si(OH)₄ + 4ROH → Si(OR)₄ + 4H₂O