Just like lithium and beryllium in Groups Land 2, boron also shows anomalous behaviour. In general, the boron chemistry resembles that of silicon (occupying a diagonal position in the periodic table) more closely than that of Al, Ga, In and TI. This is because of the small size and high electronegativity of boron as compared to those of Al, Ga, In and TI. Boron resembles silicon and differs from Al, Ga, In and TI in the following manner:

• Both B and Si are non metals whereas Al, Ga, In and TI are distinctly metallic in nature.
• B(OH)₃ and Si(OH)₄ are acidic in nature, AI(OH)₃, and Ga(OH)₃, are amphoteric and In(OH)₃, and Tl(OH)₃, basic in nature.
• The hydrides of B and Si are volatile, spontaneously inflammable liquids. These are readily hydrolysed by water and acids whereas aluminium hydride is a non volatile polymeric solid. Hydrides of Ga, In and Tl are not stable.
• BCl₃ and SiCI₄, are monomeric covalent compounds which are readily hydrolysed by water to B(OH)₃, and Si(OH)₄. Anhydrous AlCl₃, is also a covalent compound and exists in the form of a dimer, i.e. Al₂Cl₆,. On dissolving in water, it readily gives Al³⁺(aq) and Cl^-(aq) whereas B³⁺(aq) does not exist.
• Both B₂0₃ and Si0₂ are acidic in nature and react with metallic oxides on fusion to form borate and silicate glasses. On the other hand, Al₂0₃ is amphoteric.
• Boron reacts with more electropositive elements, i.e. metals to form borides which are very hard substances; Al, Ga, In and TI form alloys with metals.