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Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids

Which of the following are covalent solids?

  1. Iron

  2. Diamond

  3. Sodium chloride

  4. Graphite
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

Covalent solids form crystals that can be viewed as a single giant molecule made up of an almost endless number of covalent bonds. 

Each carbon atom in diamond and graphite is covalently bound to four other carbon atoms oriented toward the corners of a tetrahedron. Because all of the bonds in this structure are equally strong, covalent solids are often very hard and they are notoriously difficult to melt. Diamond is the hardest natural substance and it melts at $355^oC$.

Hence, the correct options are $B$ and $D$

Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids

Passage of current through graphite is due to :

  1. free electrons

  2. mobile electrons
  3. $p\pi-p\pi$ bonded electrons

  4. lone pair of electrons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In graphite, each carbon atom uses only 3 of its 4 outer energy level electron in covalently bonding to there other carbon atoms in a place. In graphite, electrons are spread out between the structure.

Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids
Statement: Diamond glitters because of its high refractive index.

State whether the given statement is true or false

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The diamond glitters because of its high refractive index. The refractive index of diamond is $2.414$. 
Higher is the refractive index, the more brilliance a substance has. This is because the substance can bend light rays to a higher degree. The brilliance of the diamond is also dependent on the cut if a diamond which in turn depends on the diamond cutter's skill. Greater number of refractive surfaces result in more glitter.

Hence, the given statement is $\text{true}$
Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids
Statement: Increase in pressure in ionic solids may decrease its co-ordination number.

State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pressure and temperature also influence the structure of ionic solids. The structures of chlorides, bromides and iodides of sodium, potassium and rubidium having $6:6$ Co-ordination at normal temperature and pressure changes to $8:8$ co-ordination like CsCl structure at high pressure, Thus, high pressure increases co-ordination number. Furthermore, CsCl structure changes to NaCl structure at $760$ K. Thus, high temperature decreases co-ordination number.


Hence, the given statement is $true$

Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids

Ice is an example of ............ crystal.

  1. liquid

  2. molecular

  3. ionic

  4. covalent
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Molecular Crystals: 

In these crystals, molecules occupy the lattice points of the unit cells except in solidified noble gases in which the units are atoms, where the binding is due to van der Waal's forces and dipole-dipole forces. Since van der Waal's forces are non-directional, the structure of the crystal is determined by geometric consideration only.
Ice is the common example in which dipole-dipole forces of attraction (hydrogen bonding) are active. Many organic and inorganic crystals involve hydrogen bonds. Although these are comparatively weaker but play a very important role in determining the structures of substances. Example, polynucleotides, proteins etc.

Hence, the correct option is $\text{B}$

Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids
Statement: The melting point of all substances decreases with pressure increase.

State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Melting point increases with increase in pressure. This is because , due to increased pressure molecules tend to remain in solid state. (This is the basic principle on which liquification of gas works)


Hence, the given statement is $false$.

Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids
Statement: Ionic solids do not possess molecules.

State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In ionic solids, atoms are present as ions, where cations and anions are arranged in various structure giving rise to a variety of lattices. Thus, they do not have molecules.


Hence, the given statement is $\text{true}$

Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids

Dry ice is an example of_________.

  1. ionic cystal

  2. supercooled liquid

  3. molecular crystal

  4. covalent crystal
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Molecular solid is a solid composed of molecules held together by the van der Waals forces. Because these dipole forces are weaker than covalent or ionic bonds, molecular solids are soft and have relatively low melting temperature. Pure molecular solids are electrical insulators but they can be made conductive by doping. Examples of molecular solids include hydrocarbons, ice, sugar, fullerenes, sulfur and solid carbon dioxide.

Multiple choice chemistry solid state classification of crystalline solids classification of solids introduction to solids
Assertion (A): Covalent crystals have a higher melting point.
Reason (R): Covalent bonds are stronger than ionic bonds.

Choose the appropriate answer :

  1. Both (A) and (R) are correct and (R) is the correct explanation of (A)

  2. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

  3. (A) is correct but (R) is incorrect

  4. (A) is incorrect but (R) is correct

  5. Both (A) and (R) are incorrect
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Covalent crystals (like diamond) have very high melting points because the entire structure is held by strong covalent bonds. The reason is correct because covalent bonds in these networks are generally stronger than ionic interactions in a crystal lattice.