Solid State flash cards

1. 1.How do crystalline and amorphous solids differ in long-range order?

   Crystalline solids have long-range, regular repeating order of constituent particles; amorphous solids have only short-range order and lack a periodic arrangement.

   Hint: Think regularity extending over the whole solid vs only locally.

2. 2.Why are crystalline solids called true solids while amorphous solids are pseudo-solids?

   Amorphous solids (like glass) flow very slowly over time and resemble super-cooled liquids, so they are pseudo-solids or super-cooled liquids; crystalline solids are true solids.

   Hint: Old glass panes are thicker at the bottom.

3. 3.Do crystalline solids have sharp or gradual melting points?

   Crystalline solids have a sharp, characteristic melting point; amorphous solids soften over a range of temperatures.

   Hint: Uniform bond strength melts all at once.

4. 4.Are crystalline solids isotropic or anisotropic? Why?

   Crystalline solids are anisotropic — properties (refractive index, conductivity, etc.) vary with direction because of ordered, direction-dependent arrangement. Amorphous solids are isotropic.

   Hint: Different arrangement of particles along different directions.

5. 5.What happens to a crystalline solid when cut with a sharp knife vs an amorphous solid?

   A crystalline solid gives a clean cleavage with plane surfaces; an amorphous solid cuts into pieces with irregular surfaces.

   Hint: Cleavage along lattice planes.

6. 6.Give examples of amorphous solids.

   Glass, rubber, plastics (polymers), and quartz glass (fused silica). Amorphous silica differs from crystalline quartz.

   Hint: Everyday non-crystalline materials.

7. 7.Classify solids by the nature of intermolecular forces into the four broad types.

   (1) Molecular solids, (2) Ionic solids, (3) Metallic solids, (4) Covalent (network) solids.

   Hint: Based on the binding forces holding particles.

8. 8.What are the three sub-types of molecular solids?

   (i) Non-polar (dispersion/London forces, e.g. $Ar$, $H_2$, $CO_2$), (ii) Polar (dipole–dipole, e.g. $HCl$, $SO_2$), (iii) Hydrogen-bonded (e.g. ice, $H_2O$).

   Hint: Distinguished by the type of weak force.

9. 9.State the general properties of ionic solids (hardness, m.p., conductivity).

   Hard and brittle, high melting points, insulators in solid state but conduct electricity in molten state or aqueous solution (mobile ions).

   Hint: Cation–anion electrostatic lattice; ions mobile only when free.

10. 10.Why do metallic solids conduct electricity and heat well?

    Positive metal ions sit in a sea of delocalized (free) electrons; these mobile electrons carry charge and thermal energy.

    Hint: Electron sea model.

11. 11.What is a covalent / network solid? Give examples.

    Atoms are bonded by a continuous network of covalent bonds forming a giant molecule, e.g. diamond, silicon carbide ($SiC$), quartz ($SiO_2$). Very hard, very high melting.

    Hint: Whole crystal = one big molecule.

12. 12.Why is graphite soft and a good conductor though it is a covalent solid?

    Graphite has layers of hexagonally bonded carbon; each C uses 3 bonds leaving one delocalized electron. Layers slide (soft, lubricant) and delocalized electrons conduct.

    Hint: Only 3 of 4 valence electrons are bonded.

13. 13.Define a crystal lattice.

    A crystal lattice is a regular three-dimensional arrangement of points in space representing the positions of constituent particles.

    Hint: An abstract geometric array of points.

14. 14.Define a unit cell.

    The smallest repeating three-dimensional portion of a crystal lattice which, when repeated in all directions, generates the entire lattice.

    Hint: The basic building block.

15. 15.Which six parameters characterize a unit cell?

    Three edge lengths $a$, $b$, $c$ and three angles between edges $\alpha$ (between b,c), $\beta$ (between a,c), $\gamma$ (between a,b).

    Hint: Three sides + three inter-axial angles.

16. 16.How many crystal systems and how many Bravais lattices exist in 3D?

    There are 7 crystal systems and 14 Bravais lattices.

    Hint: 7 and 14.

17. 17.State the axial relationships for the cubic system.

    $a = b = c$ and $\alpha = \beta = \gamma = 90^\circ$. Examples: $NaCl$, $Cu$, $ZnS$.

    Hint: All sides equal, all right angles.

18. 18.Which Bravais lattice types occur in the cubic system?

    Three: simple (primitive), body-centred, and face-centred.

    Hint: P, I, F for cubic.

19. 19.State the axial relationships for the tetragonal system.

    $a = b \neq c$ and $\alpha = \beta = \gamma = 90^\circ$. Example: white tin ($Sn$), $SnO_2$.

    Hint: A cube stretched along one axis.

20. 20.State the axial relationships for the orthorhombic system.

    $a \neq b \neq c$ and $\alpha = \beta = \gamma = 90^\circ$. Example: rhombic sulphur, $BaSO_4$.

    Hint: All angles 90°, all sides different.

21. 21.State the axial relationships for the hexagonal system.

    $a = b \neq c$, $\alpha = \beta = 90^\circ$, $\gamma = 120^\circ$. Example: graphite, $ZnO$.

    Hint: 120° angle between two equal axes.

22. 22.State the axial relationships for the rhombohedral (trigonal) system.

    $a = b = c$ and $\alpha = \beta = \gamma \neq 90^\circ$. Example: calcite ($CaCO_3$), $HgS$.

    Hint: Equal sides, equal but non-right angles.

23. 23.State the axial relationships for the monoclinic system.

    $a \neq b \neq c$, $\alpha = \gamma = 90^\circ$, $\beta \neq 90^\circ$. Example: monoclinic sulphur, $Na_2SO_4\cdot 10H_2O$.

    Hint: One angle tilted.

24. 24.State the axial relationships for the triclinic system.

    $a \neq b \neq c$ and $\alpha \neq \beta \neq \gamma \neq 90^\circ$. Example: $K_2Cr_2O_7$, $CuSO_4\cdot 5H_2O$.

    Hint: Least symmetric — nothing equal.

25. 25.How many Bravais lattices does the orthorhombic system have?

    Four: simple, body-centred, face-centred, and end (base)-centred. It is the only system with all four centring types.

    Hint: The richest system — 4 lattices.

26. 26.What are the three main types of cubic unit cell?

    Simple cubic (SC / primitive), body-centred cubic (BCC), and face-centred cubic (FCC).

    Hint: Corners only; corners + centre; corners + faces.

27. 27.How is a corner atom shared in a cubic unit cell? Contribution?

    A corner atom is shared by 8 unit cells, so it contributes $\dfrac{1}{8}$ to the cell.

    Hint: Eight cubes meet at a corner.

28. 28.How is a face-centred atom shared? Contribution?

    A face atom is shared by 2 unit cells, contributing $\dfrac{1}{2}$ to the cell.

    Hint: A face is common to two cells.

29. 29.How is an edge-centred atom shared? Contribution?

    An edge atom is shared by 4 unit cells, contributing $\dfrac{1}{4}$.

    Hint: Four cells meet along an edge.

30. 30.What is the contribution of a body-centred atom?

    A body-centre atom belongs entirely to that unit cell and contributes 1.

    Hint: Wholly inside, not shared.

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