Materials are the substances that make up an object. Objects, therefore, are composed of materials. Materials can be pure, consisting of only one element, or they can be made up of a mixture of several elements (also known as compounds).
Properties of materials
Materials can be very complex and consist of a mixture of substances, with each substance, in turn, being composed of several elements. Each material has different physical properties.
The properties of the material vary depending on the elements or substances of which it is composed. The properties can determine how the material behaves. See these examples of a solid and a liquid material:
Diamonds are composed of carbon atoms packed together at high pressure and heat, which turns them into a crystal and makes them very hard. The force that keeps the atoms together is so strong that diamonds are the hardest natural object known on earth.
Pure water is composed of water molecules. The forces that keep these molecules together are weaker than those operating in a solid. It is the weakness of those forces that gives water the ability to flow.
The properties of a material depend on the structure of its atoms and the forces that keep the material together. This also affects its state of aggregation or state of matter: liquids have small forces binding them together, solids have large forces, and gases have almost no forces binding them together.
Properties of solid materials
The properties of solid materials are defined by the strength of the atoms or molecules that keep them together. In the case of solids, we can distinguish between chemical and physical properties. Some of the physical properties are also known as bulk properties (see below).
Physical properties of solid materials
The physical properties of solid materials can be intensive or extensive, and their classification depends on how the property reacts to an increase in mass.
If a mass increase modifies the property, it is an extensive property. If an increase in mass does not affect the physical property, it is an intensive property. See the following list of extensive and intensive properties:
Extensive properties :
- Mass, measured in kg.
- Volume, measured in cubic units.
- Length, measured in metres.
Intensive properties :
- Density, measured in mass over volume.
- Temperature, measured in degrees (Celsius, Fahrenheit, Rankine, or Kelvin).
- Conductivity, measured in Siemens per length of material.
- Malleability, measured in pressure units.
Material colours
An extraordinary property of materials is their colours, which are caused by the reflection of light when the electromagnetic waves in the visible spectrum (light as you know it) impact an object. The way an object’s atoms or molecules are arranged also affects a material’s colour.
The property of the colour of materials is used by areas of science that study light reflected by objects to understand which elements are responsible for the composition of objects.
What is a bulk property in a solid?
Solids exhibit properties, such as density, elasticity, conductivity, etc., which determine how the atoms in the solid work together as a ‘bulk’. The bulk properties are directly related to the solid’s composition and how its atoms are bound together. These bulk properties are important in engineering applications, as they can tell us how the solid works and what forces it can withstand. Some bulk properties are listed below:
- Density, measured in kg / m ^ 3.
- Conductivity, measured in S / m ^ 3, where S is Siemens.
- Elasticity, measured in Pascals (Pa).
- Hardness, measured in Pascals.
Density
Density is described as a material’s mass per unit of volume. The volume in solids depends on how tightly packed their particles are. The elements that make up the solid can affect this, as in the following two examples:
Diamonds are denser than graphite, but both consist of carbon. The atoms in a diamond are so close and tight that they occupy less space, which is why there are more atoms in a piece of diamond than in a similar-sized piece of graphite. The density of a diamond is approximately \(3.5 g / cm^3\), that of graphite, approximately \(2.7 g / cm ^ 3\).
A piece of uranium is denser than a piece of diamond and weighs more, even when both are of the same size. The reason uranium is denser than a diamond is that a uranium atom is heavier than a carbon atom. Uranium has more particles (neutrons and protons) that make up most of the atom’s mass. The density of a diamond is approximately \(3.5 g / cm ^ 3\), that of uranium approximately \(19 g / cm ^ 3\).
Conductivity
Conductivity defines how easily a material conducts electricity. It describes how the atom’s electrons and its structure work together to move electrical charges from one place to another.
Elasticity
Elasticity is the property that tells us how easy it is to deform an object. Elastic objects deform when very little strength is applied. Examples of elastic materials include rubber and metals. Any object or material that does not deform easily is named ‘inelastic’.
Hardness
Hardness is the property that defines how strongly a material resists deformation over a small area, as, for instance, when you push the lead of a pencil into an object and the object offers resistance against the lead. A material’s hardness is related to how the atoms or substances of which it is composed are bonded together. For example, a diamond’s atoms are strongly bonded together, which makes it a hard material.
How do we measure bulk properties?
A material’s bulk properties are measured using mechanical tests. During each test, materials are exposed to forces that seek to deform, penetrate, or compress them. The experiments measure the force values against the deformations made in the object.
Every bulk property can be measured using mechanical tests. Some of these are listed below:
- Conductivity test: passing an electrical current through a material.
- Elasticity test: deforming a material by pulling it or compressing it.
- Hardness test: pushing a sharp, hard object against the material and increasing the force used to push that object.
Materials - key takeaways
- Materials are the substances that make up an object.
- The composition of a material can be simple, consisting of only one element, or very complex, consisting of several substances (which may be composed of several elements).
- Materials have intensive and extensive properties. These are related to an object’s mass or atomic composition.
- If the properties depend on a material’s mass, they are extensive.
- If the properties do not depend on a material’s mass, they are intensive.
- Bulk properties are intensive properties, which depend on how the atoms of the object work together.
- Bulk properties include hardness, elasticity, conductivity, and density. A material’s properties can be measured using various mechanical tests.
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