Solid

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.