Solid
A state of matter with tightly bound atoms and structural rigidity.
Solid is a state of matter in which atoms are tightly packed and resist moving past one another, giving the material structural rigidity and a strong resistance to external forces and pressure. Unlike liquids, solids do not flow to match their container’s shape, nor do they expand to fill all available volume like a gas. They do expand when heated, as thermal energy increases interatomic distances and reduces potential energy, but to a much lesser extent than other phases. When heated to their melting point or sublimation point, solids either melt into a liquid or sublimate directly into a gas. Melting occurs if the applied pressure exceeds the substance’s triple point pressure; otherwise, sublimation takes place. Melting points are intrinsic properties, independent of the amount of matter, and span an enormous range—from 0.10 K for helium-3 under high pressure to around 4,100 K at one atmosphere for hafnium carbonitride.
The atoms in a solid are bound in one of two ways: regular geometric lattices, forming crystalline solids such as metals and water ice, or irregular arrangements, forming amorphous solids like glass and plastic. Crystalline lattices typically organize into a few well-characterized packing structures, such as body-centered cubic. The adopted structure can change with pressure and temperature, as shown in phase diagrams. For a single species of atom or molecule, these phases are called allotropes (e.g., diamond and graphite for carbon) or polymorphs (e.g., calcite and aragonite for calcium carbonate).
Non-porous solids strongly resist compression that would reduce their volume, due to mutual repulsion of neighboring electron clouds. Some solids, especially metallic alloys, can be deformed or pulled apart with sufficient force; their resistance to deformation in different directions is quantified by elastic modulus, tensile strength, and specific strength. For most substances, the solid phase has the highest density, slightly higher than the liquid phase, so solid blocks sink in their own liquids. Exceptions include water, gallium, and plutonium. All naturally occurring elements have a melting point at standard pressure except helium (which remains liquid even at absolute zero due to zero-point energy), arsenic (which sublimes around 900 K), and carbon (which sublimes around 3,950 K). When applied pressure is released, solids rapidly re-expa
- field
- Physics, Materials Science
- known_for
- Structural rigidity, resistance to compression, crystalline and amorphous structures
- key_property
- Melting point (intrinsic property)
- common_examples
- Metals, water ice, glass, plastic
- exceptions
- Water ice (less dense than liquid), helium (remains liquid at absolute zero)
Lore & Background
Solids are one of the four fundamental phases of matter. Their atoms are tightly bound in either regular geometric lattices (crystalline solids, e.g., metals, water ice) or irregular arrangements (amorphous solids, e.g., glass, plastic). The vast majority of substances in the solid state can be arranged in one of a few ubiquitous structures, such as body-centered cubic. Solids resist compression, expansion, or external forces that would alter their shape, with the degree of resistance depending on the specific material. Unlike liquids, solids do not flow to take the shape of their container, nor do they expand to fill available volume like a gas. When heated, solids expand to a much lesser extent than liquids or gases. Upon reaching their melting point or sublimation point, solids melt into a liquid or sublimate directly into a gas. Melting occurs if the subjected pressure is higher than the substance's triple point pressure; otherwise, sublimation occurs. Melting points range from 0.10 K for helium-3 under 30 bars to around 4,100 K for hafnium carbonitride at 1 atm.
Reader's Guide
Solids are fundamental to everyday life and technology. Their structural rigidity and resistance to compression make them essential for construction, tools, and infrastructure. Metals, which are typically strong, dense, and good conductors of electricity and heat, have been used since prehistoric times for buildings, vehicles, appliances, and electrical power grids. Iron and aluminum are the most commonly used structural metals, with iron often alloyed as steel. Non-porous solids strongly resist compression due to mutual repulsion of electron clouds. Some solids, especially metallic alloys, can be deformed or pulled apart, with resistance quantified by elastic modulus and tensile strength. The vast majority of substances have solid phases with the highest density, though exceptions include water ice, gallium, and plutonium. Solids can be contiguous (rigid bodies) or aggregates (e.g., sand, gravel), where particles slip past one another, leading to perceived softness. The branch of physics dealing with solids is solid-state physics, a major branch of condensed matter physics, while materials science studies the link between composition and properties.
Did You Know?
- Solids always possess the least kinetic energy per atom/molecule relative to other phases.
- The melting point of a substance is an intrinsic property, independent of how much matter is present.
- Water ice is less dense than liquid water, causing icebergs to float and freezing water in a rigid container to explode.
- All naturally occurring elements have a melting point at standard atmospheric pressure except helium, arsenic, and carbon.
More in Thermodynamics And Statistical Mechanics 1-22
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