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CHAPTER 4: LIQUIDS AND SOLIDS ( explain the following)

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    CHAPTER 4: LIQUIDS AND SOLIDS ( explain the following)

    CLASS 11 -- CHEMISTRY
    CHAPTER 4: LIQUIDS AND SOLIDS
    Q1: explain the following:

    A
    ) Solids have high density and low compressibility.
    The close congregation and orderly arrangement of the particles (atoms, ions or molecules) in solids due to strong interactions among the particles is responsible for their high density and very low compressibility.

    B) Diamond is an insulator.

    since all the four valence electrons of each carbon atom are used up in forming four C, C sigma bonds with other carbon atoms, no mobile electrons are left in the diamond to allow the conduction of electricity . Thus diamond is an insulator.

    C) Metals are good conductors.

    Metals consist of positive metal ions which are surrounded by a sea of delocalized or mobile electrons. These mobile electrons move from one positive metal ion to another throughout the crystal lattice, thus these electrons carry the current. This accounts for metals being good conductors.

    D
    ) Graphite has a black shiny surface.
    Graphite has a layered structure i.e. it has a number of flat, parallel layers of carbon atoms. In each layer, carbon atoms are arranged in a regular flat hexagon. Moreover surface of graphite is smooth. Such arrangement of carbon atoms in each layer causes reflection and absorption of light and hence graphite has a black shiny luster.

    E. common salt is soluble in water but not in kerosene.

    Common salt (NaCl) is an ionic compound. Water molecules are polar. That have ion-dipole force with the ions of sodium chloride. Ion-dipole forces are strong and can isolate sodium and chloride ions from each other. Molecules of kerosene are non-polar, they just have weak ion-dispersion forces with the ions of sodium chloride. These weak interactions are unable to break apart the ions in NaCl.

    F. reaction involving covalent crystals is slow.

    For most of the reactions to occur bonds must be broken. Covalent bond is a strong bond; greater energy is required for its breaking. Thus the reactions of a covalent solids will be slow as all of the atoms are bound by covalent bond.

    G. solids sodium chloride is an insulator.

    Electrical conductivity is due to mobility of ions or electrons. Since none of these is possible in solid sodium chloride that's why solid sodium chloride is an insulator.

    H. metal possesses a shiny luster.

    Thus luster of the metal can be explained on the basis of mobile or delocalized electrons. When light falls on the surface of the metal, the incident light collides with the mobile electrons, which get excited. When these excited electrons revert to their original position, they give off energy in the form of light. This light is than reflected from the surface of the metal and is the basis of metallic lustre of the metal.

    I. a unit cell of a crystal possesses all the structural properties of the given crystal.

    The unit cell can be defined as the smallest unit of the crystal lattice which when repeated again and again in three dimensions gives the entire crystal. Moreover, the unit cell of sodium chloride is cubic with all the three axes of equal length and all the interfacial angles of 90 degree. Similar properties are also possess by sodium chloride crystal.


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