Solids (1) PDF

THE SOLID STATE VOCABULARY Ionic solids: have ions at lattice points,  According to the kinetic-molecular theory, a mole FIGURE 1: An iceberg...

THE SOLID STATE VOCABULARY Ionic solids: have ions at lattice points,  According to the kinetic-molecular theory, a mole FIGURE 1: An iceberg held together by electrostatic forces. of solid particles has as much kinetic energy as can float because the Molecular solids: have molecules at a mole of liquid or gas particles at the same rigid three-dimensional lattice points, held together by London temperature. By definition, the particles in a solid structure of ice keeps dispersion force, dipole-dipole, and/or must be in constant motion. For a substance to water molecules farther hydrogen bonding. apart than they are in a be a solid rather than a liquid at a given Metallic solids: have metal cations at liquid water. This, open temperature, there must be strong attractive symmetrical structure of lattice points, held together by metallic forces acting between particles in the solid. ice results from bonds. These forces limit the motion of the particles to hydrogen bonding vibrations around fixed locations in the solid. Group 18 solids: have noble gas atoms at lattice points, held together by Thus, there is more order in a solid than in a London dispersion force. liquid. Because of this order, solids are not fluid. Unit cell: is the smallest arrangement → Only gases and liquids are classified as fluids of atoms in a crystal lattice that has the same symmetry as the whole crystal.  In general, the particles in a solid are more Covalent network solids: covalently closely packed than those in a liquid. Thus, most bonded, have an atom at each lattice solids are denser than most liquids. When the point, held together by covalent bonds. liquid and solid states of a substance coexist, the Crystalline Solids: have atoms solid almost always sinks in the liquid. Solid arranged in an orderly repeating cubes of benzene sink in liquid benzene pattern. because solid benzene is more dense than liquid benzene. There is about a 10% difference in Amorphous Solids: lack the order density between the solid and liquid states of found in crystalline solids. most substances. Because the particles in a Allotrope: An element that might have solid are closely packed, ordinary amounts of different forms in a same state pressure will not change the volume of a solid. https://www.mcvts.net Malleable: (of a metal or other  The relative densities of ice and liquid water cannot be predicted based material) able to be hammered or on benzene. Ice cubes and icebergs float because water is less dense as pressed permanently out of shape a solid than it is as a liquid. Figure 1 shows the reason for the exception. without breaking or cracking. As water freezes, each H2O molecule can form hydrogen bonds with up Ductile: (of a metal) able to be drawn to four neighboring molecules. As a result, the water molecules in ice are out into a thin wire. less-closely packed together than in liquid water. Electron-sea-model: the electrons on  In the solid state, the individual particles of a substance are in fixed the surface of a metal being free to positions with respect to each other because there is not enough thermal move from one atom to another. energy to overcome the intermolecular interactions between the particles. As a result, solids have a definite shape and volume. Alloy: a metallic material that contains  Most solids are hard, but some (like waxes) are relatively soft, they are more than one element also composed of ions can also be quite brittle. (see figure 2) Substitutional alloys: a second  Solids usually have their constituent particles arranged in a regular, three- element takes the place of a metal dimensional array of alternating positive and negative ions called a atom. crystal. The effect of this regular arrangement of particles is sometimes Interstitial alloys: a second element visible macroscopically. fills a space in the lattice of metal  Some solids, especially those composed of large molecules, cannot atoms. easily organize their particles in such regular crystals and exist as Isotropic: Properties of a material are amorphous (literally, “without form”) solids. identical in all directions. e.g. Cotton candy (see figure 3) Anisotropic: Properties of a material depend on the direction 1  FIGURE 2: DIAMONDS FIGURE 3: COTTON CANDY Natural diamond is carbon crystals The shelf life of pure amorphous that forms under high temperature sucrose systems, such as cotton and pressure conditions that exist candy, can be very short. only about 100 miles beneath the earth’s surface. It is typically about 99.95 percent carbon. The other 0.05 percent can include one or more trace elements, which are atoms that are not part of the diamond’s essential https://steemit.com chemistry. Diamond is the hardest naturally Diamond’s crystal structure is occurring material known. Over 70 isometric, which means the carbon percent of diamonds are used for atoms are bonded in essentially the industrial applications and demand for same way in all directions. the material is continuously growing. https://www.premiumvape.eu  Based on their crystal structures, solids can be classified FIGURE 4: Crystalline vs. amorphous into the following categories: Crystalline solids and Amorphous solids A. CRYSTALLINE SOLIDS  Crystalline solids are the greater category of solids and include all of the different types of solids below.  In crystalline solids, particles are arranged in a regularly repeating pattern. The smallest repeating unit is called a UNIT CELL (The unit cell can be thought of as a building block whose shape determines the shape of the crystal) and the geometrical pattern of points on which the unit https://fiveable.me cells are arranged is called a CRYSTAL LATTICE  The locations of particles in a crystalline solid can be represented as points on a framework called a crystal lattice. Figure 5 shows three ways that particles in a crystal lattice can be arranged to form a cube.  Crystalline solids are ANISOTROPIC in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystals. FIGURE 5: These drawing show three of the ways particles are arranged in a FIGURE 6: Unit Cell is the smallest crystal lattice. Each sphere represents a particle. A. Particles are arranged only part (portion) of a crystal lattice. at the corners of a cube. B. There is a particle in the center of the cube. C. The crystal lattice is the symmetrical There are particles in the center if each of the six cubic faces but no particle in three-dimensional structural the center of the cube itself. arrangements of atoms, ions or molecules (constituent particle) inside a https://www.mcvts.net crystalline solid as points. It can be defined as the geometrical arrangement of the atoms, ions or molecules of the crystalline solid as points in space. https://goprep.co 2 TABLE 1 shows seven categories of crystals based on shape. Crystal shapes differ because the surfaces, or faces, of unit cells do not always meet at right angles, and the edges of the faces vary in length. The edges are labeled a, b, and c; the angles at which the faces meet are labeled α, β, and γ TABLE 1: UNIT CELL https://www.mcvts.net Crystalline solids can be classified into five three categories based on the types of particles they contain and how those particles are bonded together: atomic solids, molecular solids and ionic solids. 1. COVALENT SOLIDS (also known as molecular solids) In molecular solids, the molecules are held together by dispersion forces, dipole-dipole forces, or hydrogen bonds. Most molecular compounds are not solids at room temperature. Even water, which can form strong hydrogen bonds, is a liquid at room temperature. Molecular compounds such as sugar are solids at room 3 temperature because of their large molar masses. With larger molecules, many weak attractions can combine to hold the molecules together. Because they contain no ions, molecular solids are poor conductors of heat and electricity. FIGURE 7: NaCl Structure 2. IONIC SOLIDS: Remember that each ion in an ionic solid is surrounded by ions of opposite charge (They consist of cations and anions held together by electrostatic attractions) The type of ions and the ratio of ions deter-mine the structure of the lattice and the shape of the crystal. The network of attractions that extends throughout an ionic crystal gives these compounds their high melting points and hardness. Ionic crystals are strong, but brittle. When ionic crystals are struck, the cations and anions are shifted from their fixed positions. Repulsions between ions of like charge cause the crystal https://socratic.org to shatter. The type of ions and their radii will determine the shape they will have. 3. ATOMIC SOLIDS: It is the most diverse group; they will be divided in three sub- FIGURE 8: The most common kind of quarks has groups. a hexagonal crystal structure. a) COVALENT NETWORK SOLIDS: Atoms such as carbon and silicon, which can form multiple covalent bonds, are able to form covalent network solids. They form long chains which have rigid structure and multiple covalent bonds. The covalent network structure of quartz, which contains silicon, is shown in Figure 8. Carbon forms three types of covalent network solids—diamond, graphite, and buckminsterfullerene. An element, such as carbon, that exists in different forms at the same state—solid, liquid, or gas—is called an allotrope. https://www.mcvts.net FIGURE 9: DIAMOND is probably the most well-known carbon allotrope. The carbon The diamond structure. atoms are arranged in a lattice, which is a variation of the face-centered cubic crystal structure. It has superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. Each carbon atom in a diamond is covalently bonded to four other carbons in a tetrahedron. These tetrahedrons together form a three-dimensional network of six-membered carbon rings in the chair conformation, allowing for zero bond-angle strain. This stable network of covalent bonds and hexagonal rings is the reason that diamond is so incredibly strong as a substance. As a result, diamond exhibits the highest hardness and thermal conductivity of any bulk material. In addition, its rigid lattice prevents contamination by many elements. The surface of diamond is lipophillic and hydrophobic, which means it cannot get wet by water but can be in oil. Diamonds do not generally react with any chemical reagents, including strong acids and bases. Uses of diamond include cutting, drilling, and grinding; jewelry; and in the semi-conductor industry. 4  The graphite structure. GRAPHITE is another allotrope of carbon; unlike diamond, it is an electrical conductor and a semi-metal. It is the most stable form of carbon under standard conditions and is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. There are three types of natural graphite: 1. Crystalline flake graphite: isolated, flat, plate- like particles with hexagonal edges 2. Amorphous graphite: fine particles, the result of thermal metamorphism of coal; sometimes called meta- anthracite 3. Lump or vein graphite:occurs in fissure veins or fractures, appears as growths of fibrous or acicular crystalline aggregates It has a layered, planar structure. In each layer, the carbon atoms are arranged in a hexagonal lattice. It can conduct electricity due to the vast electron delocalization within the carbon layers; as the electrons are free to move, electricity moves through the plane of the layers. It also has self-lubricating and dry lubricating properties. It can resist temperatures up to 3000 °C. https://slideplayer.com a) Metallic solids They consist of positive metal ions surrounded by a sea of mobile electrons. The strength of the metallic bonds between cations and electrons varies among metals and accounts for their wide range of physical properties. For example, tin melts at 232°C, but nickel melts at 1455°C. The mobile electrons make metals malleable and ductile. When force is applied to a metal, the electrons shift and thereby keep the metal ions bonded in their new positions. Mobile electrons make metals, good conductors of heat and electricity. The properties of metals can be accounted for in a qualitative way by the ELECTRON-SEA-MODEL, in which the valence electrons are delocalized and are visualized as being free to move throughout the metal. FIGURE 10: Metals are not covalently bonded, but the attractions between atoms are too strong to be Van der Waals forces. In metals, https://slideplayer.com valence electrons are delocalized throughout the solid. Metallic solids as it was mentioned are good conductor, have a FIGURE 11: wide range of melting points, and are shiny, malleable, ductile, and Substitutional constituents have similar readily alloyed. They are often pure substances but may also ne atomic radii and one can substitute into the mixtures called ALLOYS. crystal lattice structure of another Alloys are materials that possess characteristic metallic properties and are composed of more than one element. The elements in an alloy can be distributed either homogeneous or heterogeneous. They typically retain a sea of mobile electrons and so remain conducting. Some of their properties can be understood in terms of the size of the components of the atoms. http://weebly.com i. INTERSTITIAL ALLOYS: form between atoms of different radius. They make the lattice more rigid, decreasing https://www.unf.edu malleability and ductility. e.g. Steel, in which carbon occupies the interstices in iron. 5  Interstitial constituents have different atomic radii and the smaller fits into the interstitial spaces (lattice holes) of another. ii. SUBSITUTIONAL ALLOY: form between atoms of comparable radius, where one atom substitutes for the other in the lattice. The density typically lies between those of the component metals, it remains malleable and ductile. e.g. Brass in which copper atoms are substituted with a different element, usually zinc. http://weebly.com https://www.unf.edu b) GROUP 18 SOLIDS: This group is known as noble gasses, but once cooled below their respective melting points, they form an ordered solid. These are useful in providing a place for electrons to become trapped or reactions to take place. When they are crystalized, they are very unstable. Some examples include the use of solid argon to study highly reactive molecules, and solid neon to allow reaction and formation of xenon hydrides. FIGURE 12: Small gaseous atoms or molecules such as Xe or CH4 can occupy cavities in a lattice of hydrogen-bonded water molecules to produce a stable structure. (The hydrogen atoms of the water molecules have been omitted for clarity.) Warming the solid hydrate or decreasing the https://saylordotorg.github.io pressure of the gas causes it to collapse easily.. 6 TABLE 2: CRYSTAL SOLIDS SOLID TYPE OF FORCES BETWEEN PROPERTIES EXAMPLE TYPE PARTICLES MOLECULES Argon, Methane MOLECULAR SOLID Most are solids at room temperature. Low melting point Sucrose, Dry ice Atoms or Dipole-dipole, London They are usually soft and break down easily. Water, I2, molecules dispersion and Poor conductors of heat and electricity NH3 (ammonia), hydrogen bond. Low density CO2 (Carbon dioxide), Dull surface C12H22O11 (table sugar) Very soluble in polar substances High melting point Positive and Ionic bond Hard negative ions (electrostatic Salt, KBr, CaCO3 SOLID Brittle IONIC interaction) Poor conductivity Shatter under stress Relatively dense Dull surface Covalent network solid They break before bending (diamond) Soft to hard Atoms connect Very stable diamond (C) in a network of Covalent bond Very high melting point (diamond 3550° C) graphite (C) covalent bonds Often poor conductivity (Exception→ graphite quartz (Si O2) does conduct heat and electricity) Graphite→ good lubricant Melting points depend strongly on electron ATOMIC SOLID Atoms configuration. surrounded by Tin 232°C Nickle 1455°C All metallic elements Metallic solid mobile valence Metallic bond Varies in hardness. Cu, Fe, Al electrons Good conductors of heat and electricity Easily deformed under stress → malleable and ductile Usually, high density Lustrous Group 18 solid Hard to convert them to solid state. Neon Atoms London dispersion Tend to be unstable when they are crystals. Xenon 7  B. AMORPHOUS SOLIDS FIGURE 13:  An amorphous solid is one in which the particles Native Americans use the glass-like amorphous rock obsidian to make arrowheads and knives, because it can are not arranged in a regular, repeating pattern. form sharp edges when broken. Obsidian rocks form when It does not contain crystals. lava cools too quickly to form crystals.  The term amorphous is derived from a Greek word that means without shape. But it does not mean that they are soft and flexible.  They melt gradually so they do not have a specific melting point.  Amorphous solids are ISOTROPIC in nature, that is, some of their physical properties like electrical resistance or refractive index show the same values when measured along different directions in the same crystals.  An amorphous solid often forms when a molten material cools too quickly to allow enough time for crystals to form. Figure 13 shows an example of an amorphous solid.  Glass, rubber, and many plastics are amorphous https://www.mcvts.net solids. → Recent studies have shown that glass might have some structure. When X-ray diffraction is used to study glass, there appears to be no pattern to the distribution of atoms. When neutrons are used instead, an orderly pattern of silicate units can be detected in some regions. Researchers hope to use this new information to control the structure of glass for optical applications and to produce glass that can conduct electricity. → Some properties of the amorphous solids are: i. Lack of a long range order Amorphous solids do not have a long-range order of arrangement of their constituent particles. However, they may possess small regions of orderly arrangement. These crystalline parts of an otherwise amorphous solid are known as crystallites. ii. No sharp melting point Amorphous solids do not have a sharp melting point but melts over a range of temperatures. For example, glass on heating first softens and then melts over a temperature range. Glass, therefore, can be molded or blown into various shapes. Amorphous solid does not possess the characteristic heat of fusion. iii. Conversion into crystalline forms Amorphous solids, when heated and then cooled slowly by annealing, becomes crystalline at some temperature. That is why glass objects of ancient time look milky because of some crystallization having taken place. 8 TABLE 3: CRYSTAL SOLIDS vs. AMORPHOUS SOLIDS PROPERTY CRYSTALLINE SOLID AMORPHOUS SOLIDS The constituent particles, atoms, ions or The constituent particles are arranged in STRUCTURE molecules are arranged in regular and irregular three-dimensional patterns definite three-dimensional patterns. CUTTING WITH Give clean, sharp cleavage. Unclean cleavage A KNIFE COMPRESSIBILITY Rigid and incompressible. Usually rigid and can not be compressed to any appreciable extent. MELTING POINT They have a sharp and definite melting Melting point is not definite. Melt over a point. range of temperatures. HEAT OF FUSSION Definite Not definite PHYSICAL These are anisotropic in their physical These are isotropic, that is their physical PROPERTIES properties are not identical in all properties are identical in al directions. directions. 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