Matter, properties of matter : Solid crystalline and amorphous polymorphism and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam

Matter, properties of matter : Solid crystalline and amorphous polymorphism and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam

There are two types of solid Crystalline Solid and Amorphous Solid.

Table 1 – Crystalline and amorphous states

Amorphous solids Crystalline solids
Solids that don’t have definite     geometrical shape. They have characteristic geometrical shape
Amorphous solids don’t have      particular melting point. They melt      over a wide range of temperature. Physical properties of crystalline solids are  different in different directions. This  phenomenon is known as Anisotropy.
Physical properties of amorphous      solids are same in different      direction,i.e. amorphous solids are      isotropic When crystalline solids are rotated about an  axis, their appearance does not change. This  shows that thay are symmetrical
Amorphous solids are unsymmetrical Crystalline solids cleavage along particular  direction at fixed cleavage planes.
Amorphous solids don’t break at fixed      cleavage planes.  

 

Crystalline solid: The crystalline solids are of six types according to bond length and bond angle determined by xray crystallography methods.

The structural unit of crystalline solid is arranged in fixed geometric patterns for letters. Crystalline solid generally exhibits a different shape and an orderly arrangement of units. These generally have a sharp melting point. The various crystalline solids have been divided into six distances formed. This includes in the tabular form.

Table 2 – Shape and examples of crystalline solid

Shape Example
Cubic NaCl
Tetragonal Urea
Hexagonal Iodoform
Rhombic Iodine
Monoclinic Sucrose
Triclinic Boric acid

 

Crystalline solids are falling on four categories:

Table 3 – Types of crystalline solids

Type of solid Forces holding particles together Properties Examples
Ionic Ionic High melting point, brittle, hard, non conductors as solid, good conductors as liquids or when dissolved in water NaCl, MgO
Molecular Hydrogen bonding, dipole-dipole, London dispersion Low melting point, nonconductors H2, CO2
Metallic Metallic bonding Variable hardness and melting point (depending upon strength of metallic bonding), good conductors as solids and liquids Fe, Mg
Covalent Covalent bonding High melting point, hard, non conductors C(Diamond), SiO2 (Quartz)

 

Amorphous Solid: Unlike crystalline solids, the structural units in amorphous solids are arranged in a random manner. Amorphous solid may be considered as super cooled liquids. Example of solids includes glass wood plastic etc. Amorphous solids do not have a sharp melting point and melt within some narrow range of temperature. These are in general more soluble than crystalline solids.

  • What is the difference between glassy and amorphous?

Glassy systems feature the phenomenon of glass transition: transition from super cooled liquid –> amorphous solid (glass); however, all amorphous systems do not necessarily arise from such phenomenon. Consequently, all amorphous materials are not necessarily glasses.

Polymorphism: Polymorphism is the ability of solid materials to exist in two or more crystalline forms with different arrangements or conformations of the constituents in the crystal lattice. These polymorphic forms of a drug differ in the physicochemical properties like dissolution and solubility, chemical and physical stability, flow ability and hygroscopicity. These forms also differ in various important drug outcomes like drug efficacy, bioavailability, and even toxicity. Polymorphic studies are important as a particular polymorph can be responsible for a particular property which might not be exhibited by any other form.

Different polymorphic forms of a substance usually exhibit different melting points, x-ray diffraction patterns, solubilities, dissolution behavior, stability and biological activity. A number of pharmacological actives substances such as chloramphenicol, novobiocin, sulphonamides, barbiturates, steroids such as cortisone, testosterone, prednisolone etc, have been shown to exhibit a number of polymorphic forms different in their solubility, stability and pharmacological activity. Many organic substances such as tristearin and theobroma oil also exhibit polymorphism. Theobroma oil (cocoa butter) exhibits four different polymorphic forms viz., α, β, β’and γ forms differing in their respective melting points.

Polymorphic purity of drug samples can be checked using techniques such as powder X-ray diffraction, IR/Raman spectroscopy, and utilizing the differences in their optical properties in some cases.

 

Multiple choice questions (MCQs)

1.The state of matter in which particles are arranged in either a crystalline or an amorphous form is

a)Liquid

b)Gas

c)Solid

d)Fluid

2.On increasing the temperature of amorphous solid they

a)Melt at specific temperature

b)Soften gradually

c)Break at specific temperature

d)Boil at specific temperature

3.Solids whose atoms arrange themselves in different forms are

a)Isotopes

b)Crystals

c)Allotropes

d)Amorphous

4.In graphite, the carbon atoms are arranged in layers of

a)Pentagonal arrays

b)Heptagonal arrays

c)Octagonal arrays

d)Hexagonal arrays

5.An ordered, repeating three-dimensional arrangement of particles makes up a

a)Crystalline solid

b)Amorphous solid

c)Non crystalline solid

d)None of the above

6.Diamonds are hard and

a)Do not conduct electricity

b)Bear high melting point

c)Bear high boiling point

d)All of the above

7.Giant ionic structures are also name given to

a)Ionic lattice

b)Crystal lattice

c)Metallic lattice

d)Covalent lattice

8.NaCl possess which shape?

a)Cubic

b)Tetragonal

c)Hexagonal

d)Rhombic

9.Graphite have high boiling and melting points but they are

a)Soft

b)Non conductors of heat

c)Non conductors of electricity

d)Hard

10.Ionic compounds possess the properties

a)Hard

b)Brittle

c)Soluble

d)All of the above

11.Ionic compounds only conduct electricity when they are in a state

a)Solid

b)Liquid

c)Gas

d)Molten

12.Each carbon atom forms four covalent bonds with other carbon atoms arranging them tetrahedral in

a)Graphite

b)Diamond

c)Silicon

d)Brass

13.The carbon atoms are arranged in planar layers in

a)Tin

b)Graphite

c)Diamond

d)Mercury

14.The metallic lattice is surrounded by the sea of

a)Protons

b)Electrons

c)Neutrons

d)None of the above

15.The three dimensional arrangement with the alternating ions is present in

a)Ionic lattice

b)Crystal lattice

c)Covalent lattice

d)Metallic lattice

Solutions: 

  1. c) solid
  2. b) soften gradually
  3. c) allotropes
  4. d) hexagonal arrays
  5. a) crystalline solid
  6. d) all of the above
  7. a) ionic lattice
  8. a)Cubic
  9. a) soft
  10. d) all of the above
  11. d) molten
  12. b) diamond
  13. b) graphite
  14. b) electrons
  15. a) ionic lattice

 

References:

1. GAURAV KUMAR JAIN – THEORY & PRACTICE OF PHYSICAL PHARMACY, 1st edition 2012 Elsevier, page no. 8-12.

2. Martins Physical Pharmacy, 6th edition 2011, page no. 60-68.

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