{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

PAGE6_CRUCICAL - 2 THE SOLID STATE Synopsis INTRODUCTION...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Synopsis: INTRODUCTION: Solids are characterized by their high density and low compressibility as compared to those of the gas phase. The properties of solids indicate that the molecule (or ions) in them are relatively close together. Solids can be broadly classified into two categories, namely, crystalline and amorphous solids. The main characteristics of these are described in the following. Crystalline Solids: The outstanding characteristics of a crystal are its sharp melting point, its flat faces and sharp edges. These properties are due to a high degree of internal order which extends throughout the crystal (a definite pattern constantly repeating in space). This is know as long-range order. Amorphous Solids: Amorphous solids do not have the long-range order but have a short-range order. This characteristics may not be found around a similar atom placed at a distance from the other atom. Examples of amorphous solids are glass, used silica, rubber and polymers. Amorphous solids do not have the characteristics as possessed by crystalline solids. In many ways, they are more closely related to liquids than to the crystalline solids and are, therefore, regarded as supercooled liquids with high viscosity. A given material may be converted into the amorphous or glassy form by rapidly cooling the melt or freezing the vapour. CLASSIFICATION OF CRYSTALS BASED ON BOND TYPE The properties of most of the crystals are found to conform to one of the four general types of chemical bonds, in terms of which it is possible to classify them into four categories as described in the following. Molecular Crystals (or van der Waals Crystals): Molecular crystals are those in which the crystalline state is composed of an aggregate of discrete molecules held together by van der Waals forces. Because of these weaker forces, molecular crystals are soft and posses comparatively low melting points. Examples are CO 2 , CCl 4 , Ar and most of the organic compounds. Ionic Crystals: Ionic crystals involve electrostatic forces amongst their structural units. Because of stronger forces, ionic crystals are strong and likely to be brittle. The melting points are high, which decease with increasing size of the ions. In ionic crystals, some of the atoms may be held together by covalent bonds to form ions having definite positions and orientations in crystal lattice. Covalent Crystals: Covalent crystals involve forces of chemical nature (covalent bonds) extended in three dimensions. These forces are strong, and consequently the crystals are strong and hard, with high melting points. Examples are diamond, silicon, etc. Metallic crystals: Electrons are held loosely in these type of crystals. They are god conductors or electricity.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern