What do two or more elements chemically united in a definite proportion by weight form?

When two or more elements are chemically united in a definite proportion by weight, they form a compound. Compounds are substances that result from the chemical combination of elements, where the elements are bonded together in specific ratios and configurations. This definitive ratio is crucial because it determines the compound's properties and behaviors.

For example, water (H2O) is a compound formed from hydrogen and oxygen in a 2:1 ratio. The chemical bonds between these atoms create a new substance with characteristics that are different from those of the individual elements.

In contrast, a mixture consists of two or more substances that are physically combined but not chemically bonded, meaning they retain their individual properties. A solution is a specific type of mixture where one substance (the solute) is dissolved in another (the solvent), resulting in a homogeneous mixture. An alloy is a combination of two or more metals, which can have a varied composition and often involves a physical blending rather than a chemical bonding process.