Grade 9 → Matter and its nature → States of matter ↓
Solid state
When we think of matter, we usually think of the things around us such as air, water, trees, rocks, and countless other objects. Matter is anything that has mass and occupies space, and it exists in different states – primarily solid, liquid, and gas. In this discussion, we are going to focus on the solid state of matter and explore its characteristics, properties, and how it differs from other states of matter.
What is solid?
A solid is a state of matter that has structural rigidity and resistance to changes in shape or volume. Unlike liquids, a solid object does not flow to take the shape of its container, nor does it expand to fill the entire volume available to it like a gas. Instead, solids maintain a definite shape and volume. This is because the particles in a solid are very closely packed together and arranged in a definite structure.
Visual example of a solid object
Imagine marbles packed tightly in a box. When you shake the box, the marbles may move a little, but their arrangement does not change. This is similar to the arrangement of particles in a solid.
Properties of solid matter
Solids have the following characteristics:
- Definite shape and volume: Solids have a definite shape and volume. This means that they do not need a container to maintain their shape, which persists as long as physical conditions such as temperature and pressure remain constant.
- Incompressibility: Solids are generally incompressible because of the dense packing of their molecules.
- High density: Solids usually have higher densities than liquids and gases because the arrangement of their atoms or molecules is much denser. The exception to this is ice, which is less dense than liquid water.
- Low diffusion: The particles in solids do not move freely; hence, diffusion in solids is very low compared to liquids and gases.
- Rigidity: Solids are rigid and resist external forces to change their shape. This rigidity is due to the strong forces of attraction between their particles.
Understanding atomic structure in solids
To understand why solids have these properties, we need to deeply understand their atomic structure. In solids, atoms or molecules are arranged in a certain order that determines the properties of the matter. Let's explore these arrangements.
Crystalline solid
In crystalline solids, atoms, ions, or molecules are arranged in an ordered three-dimensional pattern over long distances. This regular pattern is called a crystal lattice. Examples of crystalline solids include salt, sugar, and metals such as iron and copper.
Visual example of a crystalline solid
The circles in the figure represent particles and their regular arrangement shows the crystalline structure.
Amorphous solid
Unlike crystalline solids, amorphous solids do not have long-range order. Their particles are not arranged in regular patterns. Instead, they are arranged randomly, which is why they have no obvious shape. Examples include glass and plastic.
Chemical bonding in solids
The properties of solids are determined mainly by the type of chemical bonds that hold the particles together.
- Ionic solids: These are formed by ions held together by ionic bonds. Examples include sodium chloride (
NaCl
) and magnesium oxide (MgO
). - Covalent network solids: The atoms in these solids are linked by a network of covalent bonds. Examples include diamond and quartz.
- Metallic solids: consist of metal cations surrounded by a "sea" of delocalized electrons. This structure explains the properties such as conductivity and malleability found in metals such as copper and aluminum.
- Molecular solids: held together by intermolecular forces such as London dispersion, dipole-dipole interactions, or hydrogen bonding. Examples include ice (
H2O
) and solid carbon dioxide (CO2
).
Examples of solids in daily life
Solids play an important role in our daily lives. Here are some examples of how we encounter solids in our daily lives:
- Furniture like tables and chairs in our homes are solid objects.
- The screen you are using to read this text is made of solids.
- In addition, solid substances such as minerals are important in the formation of rocks.
- Food items such as bread and butter are also examples of solids.
The role of solids in nature
Solids are important in nature, forming the physical structure of the Earth and things inside it. The Earth's crust is composed primarily of solid rocks and minerals. These solids form mountains, valleys, and various landforms. In addition, living organisms, including plants and animals, depend on solid structures for support and protection.
Physical changes in solids
Solids can also undergo physical changes without changing their chemical composition. Here are some examples:
- Melting: When a solid is heated, it can change into a liquid. This change occurs when the particles in the solid gain enough energy to be released from their fixed positions. A common example is ice melting into water.
- Sublimation: Some solid substances can change directly into gases without first going into the liquid state. A classic example of this phenomenon is dry ice (
CO2
) which sublimes directly from the solid state to the gaseous state.
Importance of solids in technology
Solids play an important role in technology and industry. For example:
- Semiconductors: Solid materials such as silicon are used in electronic devices because of their semiconductor properties.
- Construction materials: Solid materials such as steel and concrete are essential in building infrastructure.
- Metallurgy: The study and manipulation of metals is important in industries such as automotive and aerospace.
Conclusion
Understanding the solid state is fundamental to the study of matter and chemistry. The properties of solids, from their hardness to their incompressibility, arise from the way their atoms are structured and bonded. Whether in nature, technology or our everyday lives, solids are indispensable, highlighting the importance of chemistry and the study of the different states of matter.