What is Amorphous Solid?

An amorphous solid is that in which the constituent particles do not possess a regular three-dimensional arrangement.

Amorphous solids, lacking the three-dimensional long-range order of a <a href="https://byjus.com/chemistry/crystal-structure/" style="box-sizing: border-box; background-color: transparent; color: rgb(115, 173, 33); text-decoration-line: none; user-select: initial !important;">crystalline material</a>, possess a more random arrangement of molecules, exhibit short-range order over a few molecular dimensions, and have physical properties quite different from those of their corresponding crystalline states.

Properties of Amorphous Solids

Amorphous solid are sometimes described as supercooled liquid because their molecules are arranged in a random manner somewhat as in liquid state.

1. Lack of long-range order

Amorphous Solid does not have a long-range order of arrangement of their constituent particles. However, they may possess small regions of orderly arrangement. These crystalline parts of an otherwise amorphous solid are known as crystallites.

2. No sharp melting point

An amorphous solid does not have a sharp melting point but melts over a range of temperatures. For example, glass on heating first softens and then melts over a temperature range. Glass, therefore, can be moulded or blown into various shapes. Amorphous solid does not possess the characteristic heat of fusion.

3. Conversion into crystalline form

Amorphous solid, when heated and then cooled slowly by annealing, becomes crystalline at some temperature. That is why glass objects of ancient time look milky because of some crystallization having taken place.

Examples of Amorphous Solids

Examples of amorphous solids are glasses, ceramics, gels, polymers, rapidly quenched melts and thin-film systems deposited on a substrate at low temperatures. The investigation of amorphous materials is a very active area of research. Despite enormous progress in recent years our understanding of amorphous materials still remains far from complete. The reason is the absence of the simplifications associated with periodicity.

Nonetheless, from a comparison of the properties of materials in crystalline and an amorphous state the essential features of the electronic structure and thereby also macroscopic properties are determined by short-range order. Thus these properties are similar for solids in the amorphous and crystalline state.

Some examples of amorphous solids are glass, rubber, pitch, many plastic etc. Quartz is an example of a crystalline solid which has regular order of the arrangement of SiO₄ tetrahedra. If quartz is melted and the melt is cooled rapidly enough to avoid crystallization an amorphous solid called glass is obtained.

Amorphous Solids are Isotropic

Amorphous solids are isotropic. That is, they exhibit uniform properties in all directions. The thermal and electrical conductivities, coefficient of thermal expansion and refractive index of an amorphous solid have the same value in whatever direction the properties are measured.

Any given crystalline solid can be made amorphous by the very rapid cooling of its melt or by freezing its vapour. This does not allow the particles to arrange themselves in a crystalline pattern.. When quartz the crystalline form of SiO2 is melted and then rapidly cooled, an amorphous solid known as quartz glass or silica glass results. This material has the same composition SiO2 but lacks the molecular level orderliness of quartz. Amorphous form of metal alloys are obtained when thin films of melted metal are rapidly cooled. The resulting metallic glasses are strong, flexible and much more resistant to corrosion than the crystalline alloys of the same composition.

Acetylation is a chemical reaction in which a hydrogen atom is substituted for an acetyl group (CH₃C=O group) in a compound. The products formed in acetylation reactions typically have an acetoxy functional group. When the hydrogen atom belonging to an alcohol group replaced with an acetyl group in an acetylation reaction, an ester is formed as the product. For such reactions (where the reactant compound contains free hydroxyl groups), the most commonly used acetylating agent is acetic anhydride. 

The carbonyl group is basically a polar group, that is the carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. This is why aldehyde, containing the carbonyl as the principal functional group are polar in nature. Both aldehydes (R−CHO) and ketones(RCOR′) contain a C=O bond. Oxygen is more electronegative than carbon draws the electron density towards it which creates a slight positive charge over the less electronegative carbon atom and negative charge over the more electronegative oxygen atom. This creates a net dipole moment pointing from carbon towards oxygen and thus makes the compound polar.

Given density (d) = 8.55 g/cm³
Atomic mass (M) = 93u = 93 g/mol
We know, Avogadro number, N = 6.022 × 10²³
given lattice is body - centered cubic,
so, number of atoms per unit cell (z) = 2
we know, 
=> 8.55 = (2 × 93)/(a³ × 6.023 × 10²³)
=> 8.55 × a³ × 6.023 × 10²³ = 186
=> a³ = 186/(8.55 × 6.023 × 10²³)
=> a³ = 36.124 × 10^-24
=> a = 3.3057 × 10^-8 cm
for BCC unit cell, radius = √3a/4
= (√3 × 3.3057 × 10^-8)/4
= (1.732 × 3.3057)/4 × 10^-8
= 1.431 × 10^-8 cm = 1.431 × 10^-10 m
= 1.431 A°
hence, atomic radius of Niobium is 1.431A°.

The boiling point is directly proportional to the intermolecular forces existing in a compound.

In propanol, there is an intermolecular hydrogen bonding and Van der Waal's forces.

Whereas in butane weak van der Waal's force of attraction is the only forces between the molecules. Therefore, propanol has highest boiling point (391 K) as compared to that of butane (309 K)

(i) Reimer–Tiemann Reaction: Treatment of phenol with chloroform in the presence of aqueous alkali at 340 K followed by hydrolysis of resulting product gives salicylaldehyde as a major product.

(ii) Friedel–Crafts acylation of anisole: Anisole on treatment with acylchloride in the presence of anhydrous AlCl₃ undergo electrophilic substitution in the ring at ortho and para positions. For example,

(i) Reimer–Tiemann Reaction: Treatment of phenol with chloroform in the presence of aqueous alkali at 340 K followed by hydrolysis of resulting product gives salicylaldehyde as a major product.

(ii) Friedel–Crafts acylation of anisole: Anisole on treatment with acylchloride in the presence of anhydrous AlCl₃ undergo electrophilic substitution in the ring at ortho and para positions. For example,

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Brownian movement may be defined as continuous zigzag movement of the colloidal particles in a colloidal solution. It depends on the size of the particles and the viscosity of the colloid. Smaller the size of the particle and lesser its viscosity, faster is its motion. This movement is responsible for the stability of sols

Food Preservatives

• Food preservatives prevent spoilage of food due to microbial growth. The most commonly used preservatives include table salt, sugar, vegetable oils and sodium benzoate, C₆H₅COONa.
• Sodium benzoate is used in limited quantities and is metabolised in the body. Salts of sorbic acid and propanoic acid are also used as preservatives.

Organometallic Compounds are chemical compounds which contain at least one bond between a metallic element and a carbon atom belonging to an organic molecule. Even metalloid elements such as silicon, tin, and boron are known to form organometallic compounds which are used in some industrial chemical reactions.

The population growth in India is quite alarming. It needs to be stopped immediately. Following can help to curb the population explosion:

1. Spread increasing awareness among people and conduct camps and education seminars for the same. 

2. Increase the age limit for marriage and completely detain child marriages.

3. Increase the incentives to small families and promote contraception and family planing.

4. Remove social stigma associated with sexual health and educate school adolescence about the same.

Methanal ( HCHO ) can be converted into propan-1-ol ( CHCHCHOH ) by following step of reactions -

(i). React methanal ( HCHO ) with ethyl magnesium bromide ( CHCHMgBr ) , CHCHCHOMgBr is formed .

(ii). React CHCHCHOMgBr with water ( HO ) , propan-1-ol  ( CHCHCHOH ) is formed .

• Methanal is also known as formaldehyde .
• Propan-1-ol is a colorless liquid . It's molar mass is 60.09 g / mol .

A non-volatile solute does produce vapour at the boiling point of the solution. They have lower vapour pressure and higher boiling point.

Example: Sugar.

A volatile solute produces vapour at the boiling point of the solution. At the same temperature, they have higher vapour pressure than non-volatile solutes.

Examples: Alcohol, ether, mercury, and gasoline.

Haloarenes can be synthesised by any of the following reactions:

1. By electrophilic substitution reaction:

This involves the direct halogenation of benzene ring in the presence of Lewis acid catalysts like iron or iron (III) chloride.

2. By Sandmeyer’s reaction:

Aniline is treated with sodium nitrite to give a diazonium salt which is then treated with cuprous chloride or cuprous bromide to produce the corresponding aryl halide:

Coagulation is a process of aggregating together the colloidal particles so as to change them into large sized particles which ultimately settle as a precipitate. It can also be called as precipitation.

Coagulation is generally brought about by the addition of electrolyte.

When an electrolyte is added to the colloidal solution, the particles of the sol take up the ion which is oppositely charged and thus get neutralised.

Following are the three methods by which coagulation of lyophobic sols can be carried out.

(i) Electrophoresis: In this process, the colloidal particles move towards oppositely charged electrodes and get discharged resulting in coagulation.

(ii) Mixing of two oppositely charged sols: When equal proportions of oppositely charged sols are mixed, they neutralise each other resulting in coagulation.

(iii) Dialysis: By this method, electrolytes present in sol are removed completely and colloid becomes unstably resulting in coagulation.