The ability of a material to be flattened or shaped without cracking or breaking is known as malleability. This property describes how a substance reacts when subjected to compressive forces, such as being hammered or pressed into a thin sheet. Scientists categorize every measurable trait of a substance as either a physical property or a chemical property to predict its behavior and utility.
Defining Physical Properties
Physical properties are traits of a substance that can be observed or measured without causing a change in its chemical identity. The observation process might alter the material’s form or state, but the underlying chemical composition remains exactly the same. For example, when water freezes into ice, it changes state but is still composed of H2O molecules.
These properties help in identifying and describing materials and include characteristics like color, density, and odor. Density, for instance, is the ratio of mass to volume, which can be measured without altering the substance’s molecular structure. Other common physical properties include the melting point, boiling point, and hardness. Observing or measuring any of these characteristics only involves a change in the physical state or arrangement of the particles, not the creation of a new substance.
Defining Chemical Properties
Chemical properties describe a substance’s potential to undergo a transformation that results in a change in its chemical composition. These properties become evident only when the substance interacts with another substance or energy in a way that breaks and forms new chemical bonds. Observing a chemical property necessarily leads to the creation of one or more new substances with different properties than the original material.
A classic example of a chemical property is flammability, which is the ability of a material to burn or ignite, causing combustion and forming new compounds like carbon dioxide and water vapor. Reactivity is another broad chemical property that describes a substance’s tendency to undergo a chemical reaction with other materials, such as acids or oxygen. Iron’s tendency to rust when exposed to oxygen and water is a specific example, where the iron changes into iron oxide. Other instances include toxicity and the heat of combustion.
Malleability: A Physical Property
Malleability is explicitly classified as a physical property because the process of shaping a material does not change its chemical identity. When a metal is hammered or rolled into a thin sheet, the material deforms under the compressive stress, but the atoms themselves remain the same element or compound. The chemical bonds within the substance are not broken and reformed to create a new material.
This ability is particularly pronounced in metals like gold and aluminum, which can be flattened into extremely thin foils without fracturing. Gold is so highly malleable that a single gram can be pressed into a sheet covering over a square meter. At a microscopic level, this property is possible due to the unique metallic bonding structure, which allows layers of atoms to slide past one another without causing the material to break. The material’s internal structure changes its physical arrangement, but its molecular formula and chemical composition are preserved.