7/8/2013 Navrachana School, Sama. Zaid Mansuri 1 CHEMISTRY 1 Navrachana School, Sama. Navrachana School, Sama. ....Zaid Mansuri ....Zaid Mansuri The correlation between structure and properties helps in discovering new solid materials with desired properties like …… high temperature high temperature superconductors, magnetic materials, biodegradable polymers for packaging, biodegradable polymers for packaging, bio- compliant solids for surgical implants, etc. 2 Navrachana School, Sama. Navrachana School, Sama. ....Zaid Mansuri ....Zaid Mansuri
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CH 1 SOLID STATE - chemzblog – The ultimate … · 1.3 Classification of Crystalline Solids On the basis of nature of intermolecular forces operating between them, ... 1.9 Imperfections
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Amorphous solids are also called as pseudo solids or super cooled liquids.b.coz they have tendency to flow like liquids.
Window panes are thicker at bottom !
Crystalline solids are Anisotropic
i.e. some of their physical properties like
electrical resistance orrefractive index
show different values when measured alongshow different values when measured alongdifferent directions in the same crystals.( b’coz of different arrangement of particlesin different directions)
1.4 Crystal Lattices and Unit Cells1.4 Crystal Lattices and Unit Cells
Crystal lattice : A regular three dimensional arrangementof points in space is called a crystallattice.
characteristic
lattice.
There are only 14 possible three dimensional lattices. These are called BravaisLattices
Characteristics of a crystal lattice:
(a) Each point in a lattice is called lattice point or lattice site.(b) Each point in a crystal lattice represents one constituent particle which may be
an atom, a molecule (group of atoms) or an ion.(c) Lattice points are joined by straight lines to bring out the geometry of the lattice.
Example 1.1 A compound is formed by two elements X and Y. Atoms of the element Y (as anions) make ccp and those of the element X (as cations) occupy all the octahedral voids. What is the formula of the compound?
Ans : XY
Example 1.2 Atoms of element B form hcp lattice and those of the element A occupy2/3rd of tetrahedral voids. What is the formula of the compound formedby the elements A and B?
Packing efficiency = vol. occupied by 2 spheres in the unit cell x 100 %Packing efficiency = vol. occupied by 2 spheres in the unit cell x 100 %total vol. of the unit cell
An element has a body-centred cubic (bcc) structure with a cell edgeof 288 pm. The density of the element is 7.2 g/cm3. How many atomsare present in 208 g of the element?
1. Vacancy defects When some of the lattice sites are vacant, the crystal is said tohave vacancy defect (Fig. 1.23).- density of the substance decreases.-This defect can also develop when a substance is heated.- Shown by non-ionic solids
2. Interstitial defects When some constituent particles (atoms or molecules) occupyan interstitial site, the crystal is said to have interstitial defect.-density of the substance increases- shown by non-ionic solids
Note : Ionic solids must always maintain electrical neutrality. Rather than simple vacancy or interstitial defects, they show these defects as Frenkel andSchottky defects.
3. Frenkel defects When the smaller ion (usually cation) is dislocated from its normalsite to an interstitial site it is called Frenkel defect.- It creates a vacancy defect at its original site and an interstitialdefect at its new location.defect at its new location.
- Frenkel defect is also called dislocation defect.- density of the solid does not change.- shown by ionic substance in which there is a large difference inthe size of ions,
4. Schottky defects In this defect equal number of cations and anions are missing from their positions.- basically a vacancy defect.- Electrical neutrality is maintained.- density of crystal decreases- Eg : in NaCl there are approximately 106 Schottky pairs per cm3
at room temperature. In 1 cm3 there are about 1022 ions. Thus,there is one Schottky defect per 1016 ions.there is one Schottky defect per 10 ions.
- shown by ionic substances in which the cation and anion are ofalmost similar sizes.
- Eg : NaCl, KCl, CsCl and AgBr.- Note : AgBr shows both, Frenkel as well as Schottky defects.
Impurity defects When some foreign impurities replace the ions of thecrystal, the crystal is said to have Impurity defect.- e.g : SrCl2 in NaCl. Each Sr+2 replaces two Na+ ions to maintain
the stoichiometry. One site is occupied while other remains vacant (cationic vacancy).hence equal no. of cationic vacancies are generated in this case.
- O is lost as O2 reversibly.- excess of Zn+2 occupies the interstitial nearby.- thus, Zn1+xO- thus, Zn1+xO
Metal deficient defects
Many solids – difficult to prepare in stoichiometric composition- More anions than metals- Fe0.93O to Fe0.96O- some Fe+2 Fe+3 + e- to maintain the electrical neutrality of the crystal
0.93 0.96- some Fe+2 Fe+3 + e- to maintain the electrical neutrality of the crystal
Applications of n-type and p-type semi conductors :
• diode p-type and n-type semiconductors & is used as a rectifier• transistors npn & pnp amplify radio or audio signals.• photo-diode solar cells
• Combination of different group atoms to give average of 4e-s• Combination of different group atoms to give average of 4e s
gr. 12 + gr. 16 e.g: ZnS, CdS, CdSe and HgTe
gr. 13 + gr. 15 e.g: InSb, AlPb and GaAs have very fastresponse
• In these compounds, the bonds are not perfectly covalent and the ioniccharacter depends on the electronegativities of the two elements.character depends on the electronegativities of the two elements.
• interesting ! transition metal oxides (TiO, CrO2 and ReO3) behave like metals!!ReO3 is like metallic copper in its conductivity and appearance.VO, VO2, VO3 and TiO3 show metallic or insulating properties depending on temperature.
1. Paramagnetism : due to presence of unpaired electrons weakly attracted by the magnetic field magnetized in a magnetic field in the same direction lose magnetism in the absence of mag. field e.g : O2, Cu2+, Fe3+, Cr3+
Diamagnetism: • weakly repelled by a magnetic field. • eg: H2O, NaCl and C6H6• They are weakly magnetised in a magnetic field in opposite direction. • shown by those substances in which all the electrons are paired and there are no unpaired electrons. • Pairing of electrons cancels their magnetic moments and they lose their • Pairing of electrons cancels their magnetic moments and they lose their magnetic character.
Ferromagnetism: • A few substances like iron, cobalt, nickel, gadolinium and CrO2 are attracted very strongly by a magnetic field. Such substances are called ferromagnetic substances.• can be permanently magnetised. • In solid state, the metal ions of ferromagnetic substances are grouped together into small regions called domains. Thus, each domain acts as a tiny together into small regions called domains. Thus, each domain acts as a tiny magnet. • In an unmagnetised piece of a ferromagnetic substance the domains are randomly oriented and their magnetic moments get cancelled. When the substance is placed in a magnetic field all the domains get oriented in the direction of the magnetic field and a strong magnetic effect is produced. This ordering of domains persist even when the magnetic field is removed andthe ferromagnetic substance becomes a permanent magnet.
Antiferromagnetism: • Substances like MnO showing antiferromagnetism have domain structure similar to ferromagnetic substance, but their domains are oppositely oriented and cancel out each other's magnetic moment
Ferrimagnetism: • the magnetic moments of the domains in the substance are aligned in parallel and anti-parallel directions in unequal numbers. • weakly attracted by magnetic field as compared to ferromagnetic substances. • Examples: Fe3O4 (magnetite) and ferrites like MgFe2O4 and ZnFe2O4 are examples of such substances. • These substances also lose ferrimagnetism on heating and become paramagnetic.
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