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Monday, 28 September 2015

FSc Notes Chemistry Part 1 Chapter 4 Liquids and Solids Lecture 6



FSc Notes Chemistry Part 1 Chapter 4 Liquids and Solids Lecture 6


Solids:

That state of matter which has a fixed shape and volume is known as solid. The molecules of solid substance are closer enough to each other with strongest attractive forces. Such molecules can not move away from the fixed position however they undergo vibration motion at their fixed positions.
Types of Solid:
Solid are two types
(i) Crystalline solids:
Solids whose particles (ions, atoms or molecules) are properly arranged and have a specific geometric shape are known as crystalline solids. e.g. NaCl, MgO, etc.
(ii) Amorphous Solids:
Solids which do not have a specific geometric shape and whose particles are not properly arranged are known as amorphous solids. For example glass. Glass is also known as super cooled lighted.

Classification of Solids:

There are four types of solids depending upon the types bonds present in them. They are
  1. Ionic Solids
  2. Covalent Solids
  3. Metallic Solids
  4. Molecular Solids

(i) Ionic Solids

Solids whose particles (ions) are bonded to go their by means of ionic bond are known as ionic solids are ionic solids. For example NaCl, KCl, Cacl2 etc are ionic Solids.
Properties of ionic solids:
  1. Ionic solids have the following important properties.
  2. They are always in crystal form and never in liquid or gaseous state at normal conditions.
  3. They are very hard and have high melting point & boiling point and low volatility.
  4. They are bad conductors in solid state because no free ions are available. However in solution form or in molten state they are good conductors.
  5. Due to close packing of ions ionic solids have high density.
  6. The reactions of ionic crystals are very fast.

(ii) Covalent Solids

Solids whose particles are bounded together by means of covalent bonds are known as covalent solids. Such solids are mostly made of atoms of same or different elements. e.g. Diamond, Graphite etc.
Properties of Covalent solids:
  1. They are hard enough.
  2. They have high melting point. and boiling point.
  3. Die to non0availability of free electrons, they are bad conductors. However Graphite is good conductor, due to its layered structure. Free electrons are available in between these layer.
  4. Covalent crystalline solids are insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, carbon tetrachloride etc. It is important to note that some gains molecules (covalent crystals) like diamonds and silicon carbide are insoluble in any sort of solvent (whether polar or non-polar). It is because of their big size due to their big size they do not interact with the solvent molecules.
  5. Their chemical reactions are slow.

Structure of Diamond:

Diamond is an allotrope of carbon. In diamond each carbon is covalently bond with four other carbon atoms thus forming a giant molecule. Here each carbon undergoes Sp3 hybridization. Thus the SP3 hybrid orbital’s of one carbon overlap with the Sp3 hybrid orbital’s of 4 other carbon atoms thus appearing in a tetrahedral geometry. Here each bond angle is 1095. In diamond the bond length are 154 pm.


(iii) Molecular Solids:

Solids whose particles are bonded together by means of intermolecular attractive forces are known as molecular solids. For example ice is a molecular solid because in ice. H2O molecules are held together by means of hydrogen bonding (intermolecular attractive forces). Similarly sugar, iodine, sulphur, etc. are all examples of molecular solids.
Properties:
  1. They are soft and can be compressed.
  2. They have low melting point & boiling point and are volatile in nature.
  3. They are bad conductors.
  4. Polar molecular crystals are mostly soluble in polar solvents while non-polar molecular crystals are soluble in non-polar solvents.

(iv) Metallic Solids:

The solids whose particles (atoms) are bonded together by means of metallic bonds are known as Metallic solids.
All the metals are metallic solids because their atoms are bonded together by means of metallic bond. The behavior of metallic bond is different from ionic, covalent bond and Vander Waals forces. The formation of metallic bond can be explained by “Electron gas theory” which is presented by “Loren” in 1923.
According to this theory, due to large atomic size, the valence electrons of the atoms of metals get out of them and arrange around the positively charged metals ions like a pool or a gas or as a sea.
The electrons which are in b/w the positively charge metals ions are attracted by these positive ions and thus these positively charged metal ions get attached to each other. This force of attraction is known as metallic bond.
Properties:

  1. Due to strong metallic bonds metallic solids are very hard and can’t be compressed easily.
  2. They have high melting point & boiling point and are non-volatile.
  3. They are good conductors of heat and electricity because of the presence of free electrons.

Properties of Crystalline Solids.

Crystalline solids have the following important properties.
Allotropy:
The appearance of an element in more than one crystalline shapes is known as allotropy. These different crystalline shapes of an element are known as allotropes of that element. Allotropes are physically different but chemically same. For example sulphur shows two crystalline shapes i.e. Rhombic and Monoclinic.

Polymorphism:
“The appearance of a compound in more than one crystalline shape is known as polymorphism." These different crystalline shapes (forms) of a compound are known Polymorphism of that compound. Polymorphism are physically different but chemically same. For example KNO3 (compound) appears in two crystalline shapes i.e. Rhombohedral and orthorhombic. i.e.

Isomorphism:
“The appearance of different compounds in same crystalline shape is known as isomorphism”. These compounds are known as isomorphs of each other. Isomorphs are physically same but chemically different. For example. Both NaCl and MgO have cubic geometry, so they are isomorphs of each other. Similarly NaNo3 and caco3 have Rhombohedra geometry so they are isomorphs. From the above examples it is clear that isomorphs have same atomic ratio.
i.e. NaCl & MgO
       1:1        1:1
Similarly
NaNO3 & CaCO3
    1:1          1:1

 Written by: Asad Hussain

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