Test: Crystalline & Amorphous Solids (Old NCERT) - JEE MCQ

• Ionic solids or compounds are formed by the transfer of electrons from one atom to another atom.
• Hence there is always the formation of anion and cation due to opposite charges electrostatic force of attraction formed between them which holds them together.

Therefore, the correct answer is B. 

Diamond has a very high melting point (almost 4000°C) due to very strong carbon-carbon covalent bonds having to be broken throughout the structure before melting occurs. 

Explanation: 

• Each carbon atom is covalently bonded to four other carbon atoms in a diamond.
• A lot of energy is needed to separate the atoms.
• This is because covalent bonds are strong.
• This is the reason why diamond has a high melting point.

• Amorphous solids are isotropic in nature.
• The structure of amorphous solids is similar to that of liquids.
• Hence, these are also called pseudo solids or supercooled liquids.
• Isotropy of amorphous solids is due to the same irregular arrangement of constituent particles along with all the directions.
• Cotton candy is a classic example of amorphous solids. 

• Basic particle forming ice crystals are water molecules. It is a molecular crystal.

• Water molecules are arranged in a cage-like structure orderly array resulting in a crystalline structure.

• Crystalline compounds are made up of particles or molecules that are organized in a specific order, such as ice particles or water molecules, resulting in an ordered structure known as a crystalline compound.

• Crystalline solids are anisotropic in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along with different directions in the same crystals.
• This arises from different arrangements of particles in different directions.

• Due to the random organization of particles, amorphous solids have the same physical properties along with all directions or are isotropic.
• Random organization of particles also results in unequal bond strengths.
• Upon cooling, amorphous solids turn into a brittle glass-like state from a flexible rubber-like state. This is called glass transition.

Hence, the correct answer is Glass transition. 

A diamond is not considered a molecule because each carbon atom is covalently bonded with four other carbon atoms. This is what makes a diamond a network solid.

Additional Information: 

• A network solid or covalent network solid (also called atomic crystalline solids) is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. 
• Examples of network solids include diamond with a continuous network of carbon atoms and silicon dioxide or quartz with a continuous three-dimensional network of SiO₂ units.

Molecular solids consist of atoms or molecules held to each other by dipole-dipole interactions, London dispersion forces, hydrogen bonds, or any combination of these. 

Additional Information: Hydrogen bonding refers to the formation of Hydrogen bonds, which are a special class of attractive intermolecular forces that arise due to the dipole-dipole interaction between a hydrogen atom that is bonded to a highly electronegative atom and another highly electronegative atom which lies in the vicinity of the hydrogen atom. 

• An amorphous or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal.
• In brief, an amorphous solid is any noncrystalline solid in which the atoms and molecules are not organized in a definite lattice pattern. Such solids include glass, plastic, and gel.
• Quartz glass (SiO₂) is an amorphous solid due to its short range order of constituent particles. Note Quartz is a crystalline solid while quartz glass is an amorphous solid.

• We know that glass is an amorphous solid and by alternate heating and cooling, it can be converted to crystalline forms.
• Glasses of ancient monuments undergo heating due to the exposure of sun (day time) and cool at night and thus converted to partly crystalline form.
• This results in a milky appearance.

Characteristics of Crystalline solids: 

• A crystalline solid usually consists of a large number of small crystals, each of them having a definite characteristic geometrical shape.
• Crystalline solids have a sharp melting point.
• Crystalline solids are anisotropic in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along with different directions in the same crystals. This arises due to a different arrangement of particles in different directions.
• Crystalline solids can be cleaved along a definite plane, hence we get clean cleavage in the case of crystalline solids. 
• These are considered as true solids.

On the other hand, isotropy is a characteristic of amorphous solid. Therefore, it is an incorrect statement. The correct answer is D. 

Potassium chloride is an ionic compound.
Since, potassium is a metal and chlorine is a non-metal and if a metal is mixed with a non-metal it gives an ionic compound. 

In non-polar molecular solids, molecules are held by weak dispersion forces or London forces.

Additional Information:

• Non-polar molecules are composed of atoms that have a similar value of electronegativity.
• H₂, Cl₂ and I₂ are some of the typical examples.
• In non-polar Molecular solids, the comprised atoms or molecules are held together by weak dispersion forces or London forces.
• They are soft and non-conductors of electricity.
• They have low melting points and usually exist in a liquid or gaseous state at room temperature and pressure.

• Silicon due to its catenation property form network solid.
• Catenation is the ability of an atom to form bonds with other atoms of the same element.
• The compounds of silicon are reactive and not stable.

Solids form closed packed structure with negligible intermolecular space. So, they do not change their shape in presence of external pressure. Liquids have very less intermolecular spaces so even they are resistant to external pressure and does not change their shape hence are incompressible.

Note: Due to less intermolecular force of attraction, they acquire the shape of the container in which they are kept. The volume of the liquid doesn't change with pressure. Thus making them practically incompressible.

• Metals conduct electricity because they have “free electrons.” 
• Unlike most other forms of matter, metallic bonding is unique because the electrons are not bound to a particular atom.
• This allows the delocalized electrons to flow in response to a potential difference. 

Thus, metals are good conductors of electricity.

Dry ice is solid carbon dioxide which is generally used in packing frozen items is an example of molecular solid.

Additional Information: 

• Dry Ice is the common name for solid carbon dioxide (CO2).
• It gets this name because it does not melt into a liquid when heated; instead, it changes directly into a gas (a sublimation process).
• Dry Ice is manufactured by compressing and cooling gaseous CO2 under high pressure to produce liquid CO2 initially.
• Dry ice is a molecular crystal in which the crystal lattice consists of carbon dioxide molecules rather than individual carbon or oxygen atoms.

In diamond, carbon atoms are joined together by strong covalent bonds tetrahedrally which makes it an atomic crystal. 

Hence, the correct answer is Atoms. 

• Chemists have learned over time that even within a group of solids that share a similar structure (i.e., lattice), other differences affect the way the solid behaves.
• The bonds and molecular composition of a solid influence its conductivity, malleability, solubility, density and other factors.

Therefore, the correct answer is D. 

• In order to conduct electricity, a substance must have charge particles, such as electrons and ions, that are free to move freely through it.
• In the solid-state, ionic compounds such as sodium chloride and potassium chloride have their ions fixed in position and therefore these ions cannot move so solid ionic compounds cannot conduct electricity.
• However, in the molten state, ions in ionic compounds are free to flow and therefore molten sodium chloride and potassium chloride can conduct electricity.

•  Low boiling point is the property that is not exhibited by metallic solids. The reason is metallic solid's atoms are bonded with the strong molecular force of attraction because of which the bond between the atoms doesn't breaks easily.
• Very high temperature is required to break the bond between the atoms. though the boiling point varies from element to element. so, as a result, metallic solids have a strong molecular force of attraction, they do not have a low boiling point. 

• Ionic bond is much stronger than a covalent bond because it involves complete transfer of electrons because of which there is the formation of cation and anion and there exist huge electrostatic forces of attraction.
• They also have high melting and boiling point which proves that the ionic bond is very strong.

Crystalline compounds are those in which particles/molecules are arranged in proper order as in ice particles/water molecules are arranged in a cage-like ordered manner so this ordered structure is called a crystalline compound.

• Quartz (SiO₂), or silicon dioxide also known as silica has a giant covalent structure. In SiO₂, each silicon atom is covalently bonded to four oxygen atoms.
• Each oxygen atom is covalently bonded to two silicon atoms and has an extended covalent structure similar to diamond.
• The overall ratio is two oxygen atoms to each silicon atom, giving the formula SiO₂, 
• Hence, option C is the correct answer.

• The point at which the atoms may be present on the unit cell is termed as lattice point.
• It shows the position of atoms in the crystal.