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By the end of this section, you will be able to:
  • Define and describe the bonding and properties of ionic, molecular, metallic, and covalent network crystalline solids
  • Describe the main types of crystalline solids: ionic solids, metallic solids, covalent network solids, and molecular solids
  • Explain the ways in which crystal defects can occur in a solid

When most liquids are cooled, they eventually freeze and form crystalline solids , solids in which the atoms, ions, or molecules are arranged in a definite repeating pattern. It is also possible for a liquid to freeze before its molecules become arranged in an orderly pattern. The resulting materials are called amorphous solids or noncrystalline solids (or, sometimes, glasses). The particles of such solids lack an ordered internal structure and are randomly arranged ( [link] ).

Two images are shown and labeled, from left to right, “Crystalline” and “Amorphous.” The crystalline diagram shows many circles drawn in rows and stacked together tightly. The amorphous diagram shows many circles spread slightly apart and in no organized pattern.
The entities of a solid phase may be arranged in a regular, repeating pattern (crystalline solids) or randomly (amorphous).

Metals and ionic compounds typically form ordered, crystalline solids. Substances that consist of large molecules, or a mixture of molecules whose movements are more restricted, often form amorphous solids. For examples, candle waxes are amorphous solids composed of large hydrocarbon molecules. Some substances, such as boron oxide (shown in [link] ), can form either crystalline or amorphous solids, depending on the conditions under which it is produced. Also, amorphous solids may undergo a transition to the crystalline state under appropriate conditions.

Two sets of molecules are shown. The first set of molecules contains five identical, hexagonal rings composed of alternating red and maroon spheres single bonded together and with a red spheres extending outward from each maroon sphere. The second set of molecules shows four rings with twelve sides each that are joined together. Each ring is composed of alternating red and maroon spheres single bonded together and with a red spheres extending outward from each maroon sphere.
(a) Diboron trioxide, B 2 O 3 , is normally found as a white, amorphous solid (a glass), which has a high degree of disorder in its structure. (b) By careful, extended heating, it can be converted into a crystalline form of B 2 O 3, which has a very ordered arrangement.

Crystalline solids are generally classified according the nature of the forces that hold its particles together. These forces are primarily responsible for the physical properties exhibited by the bulk solids. The following sections provide descriptions of the major types of crystalline solids: ionic, metallic, covalent network, and molecular.

Ionic solids

Ionic solids , such as sodium chloride and nickel oxide, are composed of positive and negative ions that are held together by electrostatic attractions, which can be quite strong ( [link] ). Many ionic crystals also have high melting points. This is due to the very strong attractions between the ions—in ionic compounds, the attractions between full charges are (much) larger than those between the partial charges in polar molecular compounds. This will be looked at in more detail in a later discussion of lattice energies. Although they are hard, they also tend to be brittle, and they shatter rather than bend. Ionic solids do not conduct electricity; however, they do conduct when molten or dissolved because their ions are free to move. Many simple compounds formed by the reaction of a metallic element with a nonmetallic element are ionic.

This figure shows large purple spheres bonded to smaller green spheres in an alternating pattern. The spheres are arranged in a cube.
Sodium chloride is an ionic solid.

Metallic solids

Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms [link] . The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties. All exhibit high thermal and electrical conductivity, metallic luster, and malleability. Many are very hard and quite strong. Because of their malleability (the ability to deform under pressure or hammering), they do not shatter and, therefore, make useful construction materials. The melting points of the metals vary widely. Mercury is a liquid at room temperature, and the alkali metals melt below 200 °C. Several post-transition metals also have low melting points, whereas the transition metals melt at temperatures above 1000 °C. These differences reflect differences in strengths of metallic bonding among the metals.

Questions & Answers

very brief information on collision theory
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list mixtures and their components
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describe how Ethene reacts with bromine
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the principles and applications of extraction chromatographic methods in the isolation and purification of organic compounds
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what is the dislocation of CH³COOH
Abdul Reply
another name for alkane ?
adeyeye Reply
what is the chemical formula for benzene
Emmanuel Reply
Benzene C6H6
what does each group on the periodic table stand for
Chidera Reply
what's lanthanide series
kimah Reply
lanthanide series are element in the 4f block from 57 to 70
lanthanide series consist of F block element in the first series in the end of the periodic table..they are placed separately in the periodic table.because they possess different properties than rest of the elements!
whats is Dalton's law
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tony Reply
chemistry can be defined as one of the branchs of science that deals with the state and changes which matter undergoes
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what is the formula of Benzene
formula of benzene C6H6
benzene is a cyclohexane c6h6
cyclohexene C6H6
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how do you know if a periodic table is complete or not
Emmanuel Reply
just find out the alkali metals,alkaline earth metals,the halogens, noble gases and transition metals.
What is the volume of a sample of ethane at 467 K and 1.1 atm if it occupies 405 mL at 298 K and 1.1 atm?
magen Reply
If a balloon at 25∘C with 2.3 L of volume is expanded to 40.0 L, what will the new Celsius temperature be?
Practice Key Terms 8

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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