That statement is not entirely accurate. While some properties of compounds might seem like an average of the elements involved, this is often a simplification. Here's why:

Compounds exhibit emergent properties:

* Chemical bonds: When elements combine, they form new chemical bonds, changing the arrangement and interactions of their electrons. This fundamentally alters the way they behave.

* New properties: The resulting compound often possesses entirely new properties that are not simply an average of the original elements. For example, sodium (a highly reactive metal) and chlorine (a poisonous gas) combine to form sodium chloride (table salt), a stable, edible compound.

* Example: Water (H₂O) is a liquid at room temperature, while its constituent elements, hydrogen and oxygen, are both gases.

Exceptions to averaging:

* Physical properties: Some physical properties, like density or melting point, might be roughly approximated by an average. But this is not always the case, especially when considering the nature of the chemical bond and the resulting molecular structure.

* Chemical properties: Chemical properties, like reactivity, are determined by the way elements share electrons and are significantly different in compounds compared to their individual elements.

In conclusion: Compounds are not just a simple blend of their constituent elements. Their properties arise from the unique interactions between the atoms, leading to emergent properties that can be very different from the original elements.