Answer;
When elements form a compound, the bonds and structure of the elements change.
Step-by-step explanation;
-Elements are substances (such as oxygen and hydrogen) that can't be split into simpler substances using chemical means. They contain only one kind of an atom. A compound on the other hand is a substance that is formed when two or more elements are chemically joined.
-A compound's properties may differ greatly from those of its component elements. For example; at room temperature both oxygen (O2) and hydrogen (H2) are gases, while water (H2O) is liquid. This means that when elements form a compound, the bonds and structure of the elements change. The atoms in a compound are joined chemically using chemical bonds, such as covalent bonds, ionic bond and hydrogen bonds among others.