Solid
A solid is defined as that form of matter which posseses rigidity and hence posseses a definite shape and a definite volume.
एक ठोस को उस पदार्थ के रूप में परिभाषित किया जाता है जिसमें कठोरता होती है और इसलिए इसका एक निश्चित आकार और एक निश्चित आयतन होता है।
The following are the characteristic properties of the solid state.
- They have definite mass,volume and shape.
- Intermolecular distance are short.
- Intermolecular forces are strong.
- Their constituent particles(atom,molecules or ions) have fixed positions and can only oscillate about their mean positions.
- They are incompressible and rigid.
Solid can be classified in two classes:
CRYSTALLINE SOLIDS
The substances whose constituents particles are arranged in a difinite orderly arrangement are called crystalline solids.
for Example:-
Nacl , S , diamond , sugar etc.
क्रिस्टलीय ठोस में चट्टानें, लकड़ी, कागज और कपास शामिल हैं। ये ठोस एक निश्चित पैटर्न में व्यवस्थित परमाणुओं से बने होते हैं। जब क्रिस्टलीय ठोसों को गर्म किया जाता है, तो द्रव में परिवर्तन, जिसे गलनांक कहते हैं, तेज और स्पष्ट होता है।
The crystalline substances have sharp melting point and have physical
properties Different in Different directions, i.e Crystalline
substances are ANISTROPIC.They have long range order.
क्रिस्टलीय पदार्थों में तेज गलनांक होता है और भौतिक गुण अलग-अलग दिशाओं में भिन्न होते हैं, अर्थात क्रिस्टलीय पदार्थ ANISTROPIC होते हैं। उनके पास लंबी दूरी का क्रम होता है।
AMORPHOROUS SUBSTANCES
the substances whose constituents are not arranged in an orderly arrangement are called amorphous substances.
for example
- glass ,rubber,fused silica,plastics etc.
- they do not have sharp melting points and their physical properties are same in all directions,i.e there are isotropic.
- they have short range order.
- कांच, रबर, जुड़े सिलिका, प्लास्टिक आदि , अनाकार ठोस में रबर, कांच और सल्फर शामिल हैं। उनके पास तेज गलनांक नहीं होते हैं ।और उनके भौतिक गुण सभी दिशाओं में समान होते हैं, अर्थात समस्थानिक होते हैं।
- उनके पास शॉर्ट रेंज ऑर्डर है।
The Difference in their Characteristics are:
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Crystalline Solids |
Amorphous solids |
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Arragement of constituents- Crystalline Solid have orderly arrangement of consituents. Thus they have definite regular geometry. |
Amorphous Substances do not posses an orderly arrangement. |
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Law of constancy of interfacial angles : This law states that angle between adjacent corresponding faces of the crystal of a particular substance is always constant inspite of different shapes and sizes. ... This law is also known as Steno's Law. |
Amorphous substance are not bound by plane faces;so do not posses interfacial angles. |
|
Anisotropy- Crystalline solids exhibit anisotropy i.e their physical properties are different directions.
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Amorphous substance like liquids have properties same in all directions.therefore,they are called to be isotrophic. |
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Melting Points- Melting points in crystalline solids are sharp and distinct. |
These do not have sharp melting points points e.g glass on heating softens and starts following. |
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Heat of fusion- These have definite heat of fusion. |
Amorphous solids do not have definite heat of heat of fusion . |
|
Nature- They are true solids. |
Pseodo solids or super cooled liquids. |
|
Order in arrangement of constituent particles- Long range order |
Only short range order. |
Why are solids Rigid?
Ans:-At sufficiently low temperature,the thermal energy is low and intermolecular forces between the particles(atomic ions or molecules) of a solid bring them so close that they cling to one another and occupy fixed positions.These can still oscillate to and fro about their mean position.thus solid are rigid.
Why do solids have a definite volume ?
Ans:-For a given mass of a solid,its density has fixed value.Hence a solid has a definite volume.
[Volume= Mass/density]
Why is glass considered a super-cooled liquid?
Ans- Because of its property to flow and its high viscosity,glass is considered a super-cooled liquid.
प्रवाह की अपनी संपत्ति और इसकी उच्च चिपचिपाहट के कारण, कांच को सुपर-कूल्ड तरल माना जाता है।
Refractive index of a solid is obseved to have the same value along all directions.Comment on the nature of this solid.Would it show cleavage property?
Ans:- The solid whose refractive index has same value all directions is an Amorphous solid and is isotropic in nature.When such a solid is cut with a sharp edged tool,it will cut into two pieces with irregular surfaces,i.e,it does not show cleavage property.
जिस ठोस के अपवर्तनांक का मान सभी दिशाओं में समान होता है, वह अनाकार ठोस होता है और प्रकृति में आइसोट्रोपिक होता है। जब इस तरह के ठोस को तेज धार वाले उपकरण से काटा जाता है, तो यह अनियमित सतहों के साथ दो टुकड़ों में कट जाएगा, अर्थात यह दरार गुण नहीं दिखाता .
Classify the following as amorphous or crystalline solids: Polyurethane,naphthalene,benzoic acid,teflon,potassium nitrate,cellophane,polyvinyl chloride,fiber glass,copper.
Ans- Crystalline solids are: Potassium nitrate,copper,benzoic acid,napthalene.other are amorphous
Classification of Crystalline solids
1. Molecular solids-These solid have molecules as constituent particles.They are further subdivided into two parts.
(i)Non-polar molecular solids-
They comprise of either atoms,e.g, argon and helium or the molecules formed by non-polar covalent bonds,for example H2,Cl2 and I2 .They are held by weak dispersion force or london forces.These solids are soft and non-conducture of electricity.They have low melting points and are usually liquids or gases at room temperature and pressure.
इनमें या तो परमाणु होते हैं, उदाहरण के लिए, आर्गन और हीलियम या गैर-ध्रुवीय सहसंयोजक बंधों द्वारा निर्मित अणु, उदाहरण के लिए H2,Cl2 और I2 । वे कमजोर फैलाव बल या लंदन बलों द्वारा धारण किए जाते हैं। ये ठोस नरम और गैर-संचालन हैं बिजली। उनके पास कम पिघलने वाले बिंदु होते हैं और आमतौर पर कमरे के तापमान और दबाव पर तरल पदार्थ या गैस होते हैं।
(ii)Polar molecular solids-
The molecules of substance like HCl and SO2 etc formed by polar covalent bonds.The molecules in such solids are held together by relatively stronger dipole-dipole intractions.They are soft solids and non-conducture of electricity.their melting points are higher than non-polar molecular solids.They are mostly liquids and gases at room temperature and pressure of such solids.
(iii). Hydrogen bonding molecular solids-
The molecules of such solids contains polar covalent bonds between H and F or N atoms.Strong Hydrogen bonding binds molecules of such solid like H2O(ice).They are non-conductors of electricity.Generally they are volatile liquid or soft solids under room temperature and pressure.
ऐसे ठोस के अणुओं में H और F या N परमाणुओं के बीच ध्रुवीय सहसंयोजक बंध होते हैं। मजबूत हाइड्रोजन बंधन H2O (बर्फ) जैसे ठोस के अणुओं को बांधता है। वे बिजली के गैर-संचालक होते हैं। आम तौर पर वे कमरे के तापमान के तहत वाष्पशील तरल या नरम ठोस होते हैं। और दबाव।
2. Ionic solids—
Made up of positive and negative ions and held together by electrostatic attractions. They're characterized by very high melting points and brittleness and are poor conductors in the solid state. An example of an ionic solid is table salt, NaCl.
सकारात्मक और नकारात्मक आयनों से बना है और इलेक्ट्रोस्टैटिक आकर्षण द्वारा एक साथ रखा गया है। वे बहुत उच्च गलनांक और भंगुरता की विशेषता रखते हैं और ठोस अवस्था में खराब संवाहक होते हैं। आयनिक ठोस का एक उदाहरण टेबल सॉल्ट, NaCl है।
3.Metallic Solids-
Metals are orderly collection of positive ions(Kernels) Surrounded by and held together by a sea of mobile or free electrons.These mobile electrons are responsible for high electrical and thermal conductivity of metals.They are also responsible for colour and lustre of Metals.Metals are Highly malleable and ductile.
धातुएँ धनात्मक आयनों (कर्नेल्स) का व्यवस्थित संग्रह हैं, जो मोबाइल या मुक्त इलेक्ट्रॉनों के समुद्र से घिरे और एक साथ हैं। ये मोबाइल इलेक्ट्रॉन धातुओं की उच्च विद्युत और तापीय चालकता के लिए जिम्मेदार हैं। वे धातुओं के रंग और चमक के लिए भी जिम्मेदार हैं। धातु अत्यधिक निंदनीय और तन्य हैं।
4. Covalent or Network Solids-
A wide variety of Crystalline solids of non-Metals Results from the formation of covalent bonds between adjacent atoms throughout the crystal.They are gaint-sized molecules.Covalent bonds are strong and directional in nature.such solids are hard and brittle.they have extremly high melting points and even decompose.Diamond and silicon carbide(SIC) are typical examples of such solids.Graphite is soft and conductor of electricity.
गैर-धातुओं के क्रिस्टलीय ठोस पदार्थों की एक विस्तृत विविधता सहसंयोजक के गठन से उत्पन्न होती है पूरे क्रिस्टल में आसन्न परमाणुओं के बीच बंधन। वे लाभ-आकार के होते हैं अणु। सहसंयोजक बंधन प्रकृति में मजबूत और दिशात्मक होते हैं। ऐसे ठोस कठोर होते हैं और भंगुर। उनके पास अत्यधिक उच्च पिघलने वाले बिंदु होते हैं और यहां तक कि विघटित भी होते हैं। हीरा और सिलिकॉन कार्बाइड (एसआईसी) ऐसे ठोस पदार्थों के विशिष्ट उदाहरण हैं। ग्रेफाइट नरम और बिजली का संवाहक है।
Different properties of the four types of Solid
Classify the following solids in different categories based on the nature of intermolecular forces operating them:potassium sulphate,tin,benzene,urea,ammonia,water,zinc sulphide,graphite,rubidium,argon,silicon carbide.
Ans- potassium sulphate: ionic solid,coulombic forces of attraction
Tin: metallic solid,Metallic bonding
Benzene(solid): molecular solid,dispersion or london forces.
urea:molecular solid,dipole-dipole attractions.
Ammonia:Molecular solid(polar) Hydrogen bonding.
Zinc sulphide:ionic solid coulombic forces of attraction.
Graphite: Network or covalent bonds.
Rubidium: Metallic solid,Metallic bonds(attraction between positive metal ions called kernels and mobile electrons)
argon: molecular solid,vander waal forces.
silicon carbide(SiC): Network or covalent solid.covalent bonds.
Solid A is very hard electrical insulator in solid as well as in molten state and melts at extremely high temperature.what type of solid is it.
Ans: Network or Covalent solid.
Ionic solids conduct electricity in molten state but not in solid state but not in Solid state .explain
Ans: Ions in the solid state occupy fixed positions at their lattice points in the crystal lattice.they can not move in the solid state,but can only oscilliate to and fro about their mean position.Hence they cannot conduct electricityin the solid state.while molten state,these ions break apart and become free to move.thus they conduct electricity in the molten state.
ठोस अवस्था में आयन क्रिस्टल जाली में अपने जाली बिंदुओं पर निश्चित स्थान पर होते हैं। वे ठोस अवस्था में नहीं चल सकते हैं, लेकिन केवल अपनी औसत स्थिति के बारे में आगे-पीछे हो सकते हैं। इसलिए वे ठोस अवस्था में बिजली का संचालन नहीं कर सकते हैं। पिघली हुई अवस्था में , ये आयन अलग हो जाते हैं और चलने के लिए स्वतंत्र हो जाते हैं। इस प्रकार वे पिघली हुई अवस्था में बिजली का संचालन करते हैं।
What type of solids are electrical conductors,malleable and ductile.
Ans: Metallic solids are electrical conductors,malleable an ductile.
Crystal Lattices and Unit Cells
- A regular three-dimentional arrangement of points in space is called a Crystal Lattice.
- There are only 14 Possible three-dimentional lattices.These are called BRAVAIS LATICES
Characteristics of a crystal lattice
- Each point in a lattice is called lattice point or lattice site.
- Each point in a crystal lattice represents one constituent particles which may be an atom or ion.
- Lattice points are joined by straight lines to bring out the geometry of the lattices.
Unit Cell
Unit cell is the smallest portion of a crystal lattices which,when repeated in Different directions,generates the entire lattice.
यूनिट सेल क्रिस्टल जाली का सबसे छोटा हिस्सा है, जो अलग-अलग दिशाओं में दोहराए जाने पर पूरी जाली उत्पन्न करता है।
Characteristics of a Unit Cell
- its dimension along three edges a,b and c may or may not be mutually perpendicular.
- angles between the edges,ɑ(between b and c) β(between a and c) and ℽ(between a and b).Thus, a unit cell is characterised by six parameters,a,b,c,ɑ,β, ℽ.
A portion of a three dimensional cubic lattices and its unit cell.
These parameters of a typical unit are show in figure.
Primitive and centered unit cells
Unit cells can be broadly divided into two categories,primitive and centred unit cells.
(i) Primitive Unit cells : When constituent particles are present only on the corner positions of a unit cell,it is called as primitive unit cell.
(ii) Centered Unit Cells: When a unit cell contains one or more constituent particles present at positions other than corners in addition to those at corners,it is called a centered unit cell.centered unit cells are of three types.
(a) Body-Centered Unit Cells: Such a unit cell contains one constituent particle(atom,molecules or ion) at its body-centre besides the ones that are at its corners.
(b) Face-Centered Unit cells : Such a unit cell contains one constituent particle present at the centre of its each face,besides the ones that at its corners.
(c) End-Centered unit Cells : In such a unit cell,one constituent particle is present at the centre of any two opposite faces besides the ones present at its corners.
In all,there are seven of primitive unit cells.
Number of Atoms in a Unit Cell
Primitive Cubic Unit cell:
Primitive cubic unit cell has atoms only at its corner.Each atom at a corner is shared between eight adjacent unit cells shown in figure below,Four unit cells in the same layer and four unit cells of the upper(or lower) layer.Therefore only 1/8th of an atom (molecule or ion) actually belongs to a particular unit cell.
In all,since each cubic unit cell has 8 atoms on its corners,the total number of atoms in one unit cell is 8×1/8=1 atom
Body-Centered Cubic Unit Cell
A body-Centred cubic(bcc) unit cell has an atom at each of its corners and also one atom at its body centre.
(i) 8 corners × 1/8 per corner atom=8 ×1/8= 1atom
(ii) 1 body centre of atoms per unit cell= 2 atoms
Face Centered Cubic unit cell
A face centered Cubic unit cell contains atoms at all the corners and at the centre of all the faces of the cube.Each atom located at the face-centre is shared between two adjacent unit cells and only 1/2 of each atom belongs to a unit cell.
(i) 8 corners × 1/8 per corner atom=8 ×1/8= 1atom
(ii) 6 face-centred atoms ×1/2 atom per unit cell= 6×1/2=3 atoms
total number of atoms per unit cell=4 atoms
