The elements of a compound cannot be separated from one another by physical means because they are chemically bonded together in a specific ratio and arrangement. Unlike mixtures, where the individual components retain their own properties and can be separated using physical methods such as filtration or distillation, compounds involve a chemical transformation. This alteration results in new substances with distinct characteristics.
For example, in the compound water (H2O), hydrogen and oxygen atoms are bonded to form a new substance that behaves differently from either of the gases alone. To separate hydrogen from oxygen, a chemical reaction, such as electrolysis, is necessary, which breaks the bonds between the atoms. Physical methods simply cannot achieve this type of separation, which highlights the unique and stable nature of chemical compounds.