Solid substances are those that are able to form bodies and have volume. They differ from liquids and gases in their shape. Solids retain the shape of the body due to the fact that their particles are not able to move freely. They differ in their density, plasticity, electrical conductivity and color. They also have other properties. So, for example, most of these substances melt during heating, acquiring a liquid state of aggregation. Some of them, when heated, immediately turn into a gas (sublimate). But there are also those that decompose into other substances.
Types of solids
All solids are divided into two groups.
- Amorphous, in which individual particles are arranged randomly. In other words: they do not have a clear (defined) structure. These solids are capable of melting within a specified temperature range. The most common of these include glass and resin.
- Crystal, which, in turn, are divided into 4 types: atomic, molecular, ionic, metallic. In them, the particles are located only according to a certain pattern, namely, at the nodes of the crystal lattice. Its geometry in different substances can vary greatly.
Solid crystalline substances prevail over amorphous ones in their number.
Types of crystalline solids
In the solid state, almost all substances have a crystalline structure. They differ in their structure. Crystal lattices in their nodes contain various particles and chemical elements. It is in accordance with them that they got their names. Each type has properties specific to it:
- In the atomic crystal lattice, particles of a solid are bound by a covalent bond. It stands out for its durability. Due to this, such substances have a high melting and boiling point. This type includes quartz and diamond.
- In the molecular crystal lattice, the bond between particles is distinguished by its weakness. Substances of this type are characterized by ease of boiling and melting. They are volatile, due to which they have a certain smell. These solids include ice and sugar. The movements of molecules in solids of this type are distinguished by their activity.
- In the ionic crystal lattice at the nodes, the corresponding particles alternate, charged positively andnegative. They are held together by electrostatic attraction. This type of lattice exists in alkalis, s alts, basic oxides. Many substances of this type are easily soluble in water. Due to the fairly strong bond between the ions, they are refractory. Almost all of them are odorless, since they are characterized by non-volatility. Substances with an ionic lattice are unable to conduct electric current, since they do not contain free electrons. A typical example of an ionic solid is table s alt. Such a crystal lattice makes it brittle. This is due to the fact that any shift in it can lead to the emergence of ion repulsion forces.
- In the metal crystal lattice at the nodes there are only positively charged chemical ions. Between them there are free electrons through which thermal and electrical energy passes perfectly. That is why any metals are distinguished by such a feature as conductivity.
General concepts of a rigid body
Solids and substances are practically the same thing. These terms refer to one of the 4 states of aggregation. Solids have a stable shape and the nature of the thermal motion of atoms. Moreover, the latter make small oscillations near the equilibrium positions. The branch of science dealing with the study of composition and internal structure is called solid state physics. There are other important areas of knowledge dealing with such substances. The change in shape under external influences and movement is called the mechanics of a deformable body.
Due to the different properties of solids, they have found application in various technical devices created by man. Most often, their use was based on such properties as hardness, volume, mass, elasticity, plasticity, fragility. Modern science allows the use of other qualities of solids that can only be found in the laboratory.
What are crystals
Crystals are solid bodies with particles arranged in a certain order. Each chemical substance has its own structure. Its atoms form a three-dimensionally periodic arrangement called the crystal lattice. Solids have different structural symmetries. The crystalline state of a solid is considered stable because it has a minimum amount of potential energy.
The vast majority of solid materials (natural) consists of a huge number of randomly oriented individual grains (crystallites). Such substances are called polycrystalline. These include technical alloys and metals, as well as many rocks. Monocrystalline refers to single natural or synthetic crystals.
Most often, such solids are formed from the state of the liquid phase, represented by a melt or solution. Sometimes they are obtained from the gaseous state. This process is called crystallization. Thanks to scientific and technological progress, the procedure for growing (synthesis) of various substances has gained an industrial scale. Most crystals have a natural shape in the form of regularpolyhedra. Their sizes are very different. So, natural quartz (rock crystal) can weigh up to hundreds of kilograms, and diamonds - up to several grams.
In amorphous solids, atoms are in constant oscillation around randomly located points. They retain a certain short-range order, but there is no long-range order. This is due to the fact that their molecules are located at a distance that can be compared with their size. The most common example of such a solid in our life is the glassy state. Amorphous substances are often considered as a liquid with an infinitely high viscosity. The time of their crystallization is sometimes so long that it does not appear at all.
It is the above properties of these substances that make them unique. Amorphous solids are considered unstable because they can become crystalline over time.
The molecules and atoms that make up a solid are packed with high density. They practically retain their mutual position relative to other particles and are held together due to intermolecular interaction. The distance between the molecules of a solid in different directions is called the lattice parameter. The structure of matter and its symmetry determine many properties, such as the electron band, cleavage, and optics. When a sufficiently large force is applied to a solid, these qualities can be violated to one degree or another. In this case, the solid body is subject to permanent deformation.
Atoms of solids make oscillatory motions, which determine their possession of thermal energy. Since they are negligible, they can only be observed under laboratory conditions. The molecular structure of a solid greatly affects its properties.
Study of solids
Features, properties of these substances, their qualities and the movement of particles are studied by various subsections of solid state physics.
For the study are used: radiospectroscopy, structural analysis using x-rays and other methods. This is how the mechanical, physical and thermal properties of solids are studied. Hardness, load resistance, tensile strength, phase transformations are studied by materials science. It largely echoes solid state physics. There is another important modern science. The study of existing and the synthesis of new substances are carried out by solid state chemistry.
Features of solids
The nature of the movement of the outer electrons of the atoms of a solid determines many of its properties, for example, electrical. There are 5 classes of such bodies. They are set depending on the type of atomic bond:
- Ionic, the main characteristic of which is the force of electrostatic attraction. Its features: reflection and absorption of light in the infrared region. At low temperatures, the ionic bond is characterized by low electrical conductivity. An example of such a substance is the sodium s alt of hydrochloric acid (NaCl).
- Covalent,carried out by an electron pair that belongs to both atoms. Such a bond is divided into: single (simple), double and triple. These names indicate the presence of pairs of electrons (1, 2, 3). Double and triple bonds are called multiples. There is another division of this group. So, depending on the distribution of electron density, polar and non-polar bonds are distinguished. The first is formed by different atoms, and the second is the same. Such a solid state of matter, examples of which are diamond (C) and silicon (Si), is distinguished by its density. The hardest crystals belong specifically to the covalent bond.
- Metallic, formed by combining the valence electrons of atoms. As a result, a common electron cloud appears, which is displaced under the influence of electrical voltage. A metallic bond is formed when the bonded atoms are large. They are capable of donating electrons. In many metals and complex compounds, this bond forms a solid state of matter. Examples: sodium, barium, aluminum, copper, gold. Of the non-metallic compounds, the following can be noted: AlCr2, Ca2Cu, Cu5Zn 8. Substances with a metallic bond (metals) are diverse in their physical properties. They can be liquid (Hg), soft (Na, K), very hard (W, Nb).
- Molecular, arising in crystals, which are formed by individual molecules of a substance. It is characterized by gaps between molecules with zero electron density. The forces that bind atoms in such crystals are significant. The molecules are attractedto each other only by weak intermolecular attraction. That is why the bonds between them are easily destroyed when heated. The bonds between atoms are much more difficult to break. Molecular bonding is subdivided into orientational, dispersion and inductive. An example of such a substance is solid methane.
- Hydrogen, which occurs between the positively polarized atoms of a molecule or its part and the smallest negatively polarized particle of another molecule or other part. These bonds include ice.
Properties of solids
What do we know today? Scientists have long studied the properties of the solid state of matter. When exposed to temperature, it also changes. The transition of such a body into a liquid is called melting. The transformation of a solid into a gaseous state is called sublimation. When the temperature is lowered, the crystallization of the solid occurs. Some substances under the influence of cold pass into the amorphous phase. Scientists call this process vitrification.
During phase transitions, the internal structure of solids changes. It acquires the greatest order with decreasing temperature. At atmospheric pressure and temperature T > 0 K, any substances that exist in nature solidify. Only helium, which requires a pressure of 24 atm to crystallize, is an exception to this rule.
The solid state of matter gives it various physical properties. They characterize the specific behavior of bodiesunder the influence of certain fields and forces. These properties are divided into groups. There are 3 methods of exposure, corresponding to 3 types of energy (mechanical, thermal, electromagnetic). Accordingly, there are 3 groups of physical properties of solids:
- Mechanical properties associated with stress and strain of bodies. According to these criteria, solids are divided into elastic, rheological, strength and technological. At rest, such a body retains its shape, but it can change under the action of an external force. At the same time, its deformation can be plastic (the initial form does not return), elastic (returns to its original form) or destructive (when a certain threshold is reached, decay / fracture occurs). The response to the applied force is described by the moduli of elasticity. A solid body resists not only compression, stretching, but also shifts, torsion and bending. The strength of a solid body is its property to resist destruction.
- Thermal, manifested when exposed to thermal fields. One of the most important properties is the melting point at which the body passes into a liquid state. It is observed in crystalline solids. Amorphous bodies have a latent heat of fusion, since their transition to a liquid state with increasing temperature occurs gradually. Upon reaching a certain heat, the amorphous body loses its elasticity and acquires plasticity. This state means that it has reached the glass transition temperature. When heated, the deformation of the solid occurs. And most of the time it expands. Quantitatively thisthe state is characterized by a certain coefficient. Body temperature affects mechanical properties such as fluidity, ductility, hardness and strength.
- Electromagnetic, associated with the impact on a solid substance of flows of microparticles and electromagnetic waves of high rigidity. Radiation properties are also conditionally referred to them.
Zone structure
Solids are also classified according to the so-called band structure. So, among them they distinguish:
- Conductors, characterized in that their conduction and valence bands overlap. In this case, electrons can move between them, receiving the slightest energy. All metals are conductors. When a potential difference is applied to such a body, an electric current is formed (due to the free movement of electrons between points with the lowest and highest potential).
- Dielectrics whose zones do not overlap. The interval between them exceeds 4 eV. A lot of energy is needed to conduct electrons from the valence to the conduction band. Due to these properties, dielectrics practically do not conduct current.
- Semiconductors characterized by the absence of conduction and valence bands. The interval between them is less than 4 eV. To transfer electrons from the valence to the conduction band, less energy is needed than for dielectrics. Pure (undoped and native) semiconductors do not pass current well.
The movements of molecules in solids determine their electromagnetic properties.
Otherproperties
Solid bodies are also subdivided according to their magnetic properties. There are three groups:
- Diamagnets, the properties of which depend little on temperature or state of aggregation.
- Paramagnets resulting from the orientation of conduction electrons and magnetic moments of atoms. According to Curie's law, their susceptibility decreases in proportion to temperature. So, at 300 K it is 10-5.
- Bodies with an ordered magnetic structure, with a long-range order of atoms. At the nodes of their lattice, particles with magnetic moments are periodically located. Such solids and substances are often used in various fields of human activity.
The hardest substances in nature
What are they? The density of solids largely determines their hardness. In recent years, scientists have discovered several materials that claim to be the "most durable body." The hardest substance is fullerite (a crystal with fullerene molecules), which is about 1.5 times harder than diamond. Unfortunately, it is currently only available in extremely small quantities.
Today, the hardest substance that may be used in the future in industry is lonsdaleite (hexagonal diamond). It is 58% harder than diamond. Lonsdaleite is an allotropic modification of carbon. Its crystal lattice is very similar to diamond. A cell of lonsdaleite contains 4 atoms, while a diamond has 8. Of the widely used crystals, diamond remains the hardest today.
