Category: Chemistry Notes PPT

A tabular platform of the chemical elements in the periodic table which is also called the periodic table of elements is organized by the atomic number, electron setup, and persistent compound properties. The structure of the table shows the periodic patterns. The seven lines of the table, called periods, by and large, have metals on the left and nonmetals on the right side. The segments, called groups, contain elements with approximately the same chemical behavior. Six groups have acknowledged names just as appointed numbers: for instance, group 17 elements are the halogen group; and group 18 are the noble gasses group. Additionally, shown are four basic rectangular zones or blocks related to the filling of various atomic orbitals.

The elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have been found or incorporated, finishing seven full lines of the periodic table. The initial 94 elements are all naturally occurring elements, however, some are discovered just in trace or scarce amounts and a couple of them were found in nature simply in the wake of having originally been synthesized. Elements 95 to 118 have been completely created and developed in research centers or atomic reactors. The amalgamation of elements having higher atomic numbers is as of now being pursued/analyzed: these elements would start the eighth line, and hypothetical work has been done to recommend conceivable possibilities for this augmentation. Variously manufactured radionuclides of naturally occurring elements have likewise been created in various research centers.

An Overview of the Periodic Table

Every chemical element has a unique atomic number (Z) that represents the number of protons in its nucleus. Most elements have contrasting quantities of neutrons among various atoms, with these variations being alluded to as isotopes. For instance, carbon has three normally happening isotopes: the majority of its particles have six protons and most have six neutrons also, however around one percent has seven neutrons, and an extremely little portion has eight neutrons. Isotopes are never isolated in the periodic table; they are constantly gathered together under a solitary element. Elements with no steady isotopes have the atomic masses of their most steady isotopes, where such masses are displayed, in parentheses. 

In the standard periodic table, the elements are recorded and arranged by increasing the order of atomic number Z (the number of protons in the core of an atom). Another line (period) is begun when another electron shell has its first electron. Sections (groups) are dictated by the electron setup of the particle; elements with a similar number of electrons in a specific subshell fall into similar segments (for example oxygen and selenium are in a similar segment since both of them have four electrons in the furthest p-subshell). Elements with comparative chemical properties by and large fall into a similar group in the periodic table, even though in the f-block, and to some extent in the d-block, the elements in a similar period will, in general, have approximately the same properties, too. In this manner, it is relatively simple to foresee the compound properties of an element on the off chance that one knows the properties of the elements around it.

Grouping Methods

1. Groups

A group or family is a vertical segment in the periodic table. Groups, as a rule, have more significant periodic patterns than periods and blocks. Present-day quantum mechanical speculations of atomic structure clarify group trends by recommending that elements inside a similar group, for the most part, have a similar electron arrangement in their valence shell. Consequently, elements in a similar group will, in general, have common chemistry or chemical formation and show a reasonable pattern in properties with expanding the atomic number. In certain pieces of the periodic table, for example, the d-block and the f-block, horizontal likeness can be as vital as, or more important than, vertical similarities.

According to an international level naming tradition, the groups are numbered numerically from 1 to 18 from the furthest left section (the soluble base metals) to the furthest right segment (the noble gasses). Previously, they were known by roman numerals. In America, the Roman numerals were trailed by either an ‘A’ if the group was in the s-or p-block, or a ‘B’ if the group was in the d-block.

A portion of these groups has been given minor (unsystematic) names, as found in the table, albeit some are seldom utilized. Groups 3– 10 have no minor names and are called upon, just by their group numbers or by the name of the principal individual from their group, (for example, for group 3 “the scandium group”), since they show fewer resemblances as well as vertical patterns.

Elements in a similar group will in general show patterns in the atomic radii, ionization energy, and electronegativity. From the start to finish in a group, the atomic radii of the elements increase. Since there are progressively filled energy levels, valence electrons are discovered more distant from the core. From the first one, each progressive element has lower ionization energy since it is less demanding to expel an electron since the particles are less firmly bound. 

2. Periods

A period is a horizontal column found in the periodic table. Even though groups, for the most part, have increasingly noteworthy periodic patterns, there are locales where flat patterns are more huge than vertical group patterns, for example, the f-block, where the lanthanides and actinides structure two considerable even arrangement of elements. 

Moving left to right over a period, atomic radius normally decreases. This happens because each progressive element has an additional proton and electron, which makes the electron move nearer to the nucleus. This diminishing in atomic sweep likewise makes the ionization energy increment while moving from the left to right direction over a period. The more firmly bound an element is, the more energy is required to expel an electron. Electronegativity increases in an indistinguishable way from ionization energy in view of the force applied on the electrons by the nucleus. Electron affinity likewise demonstrates a similar pattern over a period.

 

3. Blocks

Explicit groups of the periodic table can be alluded to as blocks in acknowledgment of the grouping in which the electron shells of the elements are filled. Each block is named by the subshell in which the “last” electron notionally resides. The s-block includes the initial two groups (soluble base metals and basic earth metals) and also includes hydrogen and helium. The p-block includes the last six groups, which are groups 13 to 18 in IUPAC numbering (3A to 8A in American group numbering), and contains, among different elements, the majority of the metalloids. The d-block includes groups 3 to 12 (or 3B to 2B in American group numbering) and contains the majority of the transition metals. The f-block, frequently counterbalanced beneath whatever is left of the periodic table, has no group numbers and involves lanthanides and actinides.

4. Metals, Metalloids, and Nonmetals

As per their common physical and chemical properties, the elements can be ordered into the real classes of metals, metalloids, and nonmetals. Metals are commonly lustrous, extremely conducting solids that structure amalgams with each other and salt-like ionic mixes with non-metals (other than noble gasses). A major chunk of non-metals are colorless insulating gasses; non-metals that form compounds with different non
-metals display a feature called covalent bonding. In the middle of metals and non-metals are metalloids, which have transitional or blended properties.

Metal and non-metals can be additionally grouped into subcategories that demonstrate a degree from metallic to non-metallic properties while going left to right in the lines. The metals might be subdivided into the very responsive soluble alkali metals, through the less receptive antacid earth metals, lanthanides, and actinides, utilizing the prototype transition metals, and closure in the physically and artificially frail post-transition metals. Non-metals might be just subdivided into the polyatomic nonmetals, being closer to the metalloids and demonstrating some beginning metallic character; the non-metallic diatomic nonmetals, non-metallic, and the inert, monatomic noble gasses. Particular groupings, for example, recalcitrant metals and respectable metals, are instances of subsets of transition metals, additionally known and every so often denoted.

Classifying elements and subcategories that are solely dependent on shared properties are not correct. There is an extensive uniqueness of properties inside every class with eminent covers at the limits, similar to the case with most arrangement schemes. Beryllium, for instance, is named a basic earth metal even though its amphoteric science and inclination to usually create covalent bonds are the two qualities of a chemically feeble or post-transition metal. Radon is named a non-metallic noble gas and yet has some cationic science that is normal for metals. Other arrangement plans are conceivable, for example, the division of the elements into mineralogical event classifications, or crystalline structures.

Periodic Trends and Patterns

1. Electronic Configuration

The electron setup or organization of electrons circling neutral particles demonstrates a common example of periodicity. The electrons involve a progression of electron shells (numbered 1, 2, etc.). Each shell comprises at least one subshell (named s, p, d, f, and g). 

As atomic number expands, electrons dynamically fill these shells and subshells pretty much as indicated by the Madelung principle or energy requesting rule, which has appeared in the chart. The electron pattern for neon, for instance, is 1s2 2s2 2p6. With an atomic number of ten, neon has two electrons in the main shell, and eight electrons in the second shell; there are two electrons in the s subshell and six in the p subshell.

2. Atomic Radii

Atomic radii differ in an anticipated and logical way over the periodic table. For example, the compounds, for the most part, decline along every period of the table, from the alkali metals to the noble gasses; and increase down each group. The span rises strongly between the noble gas toward the finish of every period and the alkali metal toward the start of the following time frame. These patterns of the atomic radii (and of different other compounds and physical properties of the elements) can be clarified by the electron shell hypothesis of the atom.

3. Ionization Theory

The very first ionization energy is the energy it takes to expel one electron from an atom, the second ionization energy is the energy it takes to expel a second electron from the atom, etc. For a given particle, progressive ionization energies increase with the level of ionization. Magnesium, for instance, the primary ionization energy is 738 kJ/mol and the second is 1450 kJ/mol. Electrons in the closer orbitals experience the more prominent force of electrostatic nature; in this manner, their expulsion requires progressively more energy. Ionization energy ends up being maximum to the right side of the periodic table.

4. Electronegativity

Electronegativity is the propensity of a molecule to pull in a mutual pair of electrons. An atom’s electronegativity is influenced by its atomic number and the separation between the valence electrons and the core. The higher its electronegativity, the more an element pulls in electrons and this was first projected in 1932 by Linus Pauling. Generally, electronegativity rises on going from left to right along a period and decreases on dropping a group. 

5. Electron Affinity

The electron affinity of an atom is the measure of energy discharged when an electron is added to an impartial atom to form a negative particle. Even though electron affinity changes incredibly, a few examples come up. For the most part, non-metals have more positive electron affinity values than metals. Chlorine most emphatically draws in an additional electron. The electron affinities of the noble gasses have not been estimated convincingly. 

6. Metallic Character

The lower the value of ionization energy, electronegativity, and electron affinity, the more metallic character the element has. On the other hand, the non-metallic character increases with higher estimations of these properties. Given the periodic patterns of these three properties, the metallic character will, in general, reduce while going along a period and will in general increase going down a group (or segment or family). 

7. Linking or Bridging Groups

From left to right over the four blocks of the long form of the periodic table are a progression of connecting or crossing over groups of elements, found roughly between each block. These groups, similar to the metalloids, show properties in the middle of, or that are a blend of, groups to either side. These elements are therefore known as linking or bridging groups.

Overview of Periodic Table of Elements

The periodic table of elements is the arrangement of all the chemical elements in a systematic way. We can see that the elements are arranged from left to right and top to bottom in order of increasing atomic number which coincides with increasing atomic mass.

The rows are known as the periods and the number of an element signifies the highest energy level of an electron in that element. The number of electrons in a period increases as one moves down the periodic table. Elements that occupy the same column on the periodic table have the same valence electron configurations and consequently behave similarly chemically.  

Furthermore this can also be defined as the tabular display of the chemical elements. It is very much used in chemistry, physics, and other sciences. It is a graphic formulation of the periodic law, which states that the properties of the chemical elements exhibit a periodic dependence on their atomic numbers.

Trends and Pattern of Periodic Table

Periodic tables are the patterns of the properties of chemical elements that are in the periodic table of elements.

Mainly it includes electronegativity, ionization energy, electron affinity, atomic radii, ionic radius, metallic character, and chemical reactivity.

These arise from the changes in the atomic structure of the chemical elements within their respective periods, that is rows and columns in the periodic table.

The laws help the chemical elements to be organized in the periodic table according to the atomic structures and properties.

Some of the exceptions are the ionization energy trend of group 3, the electron affinity trend of group 17, the density trend of group 1 elements (alkali metals), and so on.

Atomic Radius

This is the distance from the atomic nucleus to the outermost stable electron orbitals in an atom. It decreases across
a period from left to right because the increasing effective nuclear force on the electrons causes the atom to shrink. 

The atomic radius usually increases while going down a group due to the addition of a new energy level. However, atomic radii tend to increase diagonally, since the number of electrons has a larger effect than the sizable nucleus. 

Ionization Energy

The ionization potential is the minimum amount of energy which is required to remove one electron from each atom in a mole of an isolated, neutral, and gaseous atom. The first ionization energy is the energy required to remove the first electron, and generally, the nth ionization energy is the energy required to remove the atom’s nth electron, after the (n−1) electrons before it has been removed. 

Ionization energy tends to increase while one progresses across a period because the greater number of protons attracts the orbiting electrons more strongly, thereby increasing the energy required to remove one of the electrons.

Ionization energy and ionization potentials are not the same. The potential is an intensive property and it is measured by “volt”; whereas the energy is an extensive property expressed by “eV” or “kJ/mol”.

Electron Affinity

The electron affinity of an atom is  the energy released by an atom when an electron is added to it or  the energy required to detach an electron from a singly charged anion. 

The sign of the electron affinity can be a bit  confusing, as atoms that become more stable with the addition of an electron and show a decrease in potential energy that is the  energy gained by the atom appears to be negative.

Here the atom’s electron affinity is positive. For atoms which are less stable upon gaining an electron, potential energy increases which can be further included that  the atom gains energy. In such a case, the atom’s electron affinity is negative. However  where electron affinity is defined as the energy required to detach an electron from an anion, the energy value obtained will be of the same magnitude but have the opposite sign. This is because those atoms with a high electron affinity are less inclined to give up an electron, and so take more energy to remove the electron from the atom. In this case, the atom with the more positive energy value has a higher electron affinity. As one progresses from left to right across a period, the electron affinity will increase.

Valence Electrons

Valence electrons are the electrons in the outermost electron shell of an isolated atom of an element. In a period, the number of valence electrons increases as we move from left to right. However, in a group this periodic trend is constant, that is the number of valence electrons remains the same. 

 

Valency

Valency first increases and then decreases in the periodic table. There is no change going down a group. However, this periodic trend is  followed for heavier elements especially  for lanthanide and actinide series.

Phenolphthalein is a slightly acidic compound, hence considered a weak acid. Phenolphthalein has the chemical formula of C20H14O4and is a large organic molecule. In crystalline form, phenolphthalein appears to be white to yellow in colour. In short, it can be written as “HIn” or “php”.

 

Phenolphthalein Solution

It is readily soluble in alcohol and mildly soluble in water. So, it is dissolved in alcohol to be used in experiments. Phenolphthalein acts as an indicator in acid-base titrations.

 

Phenolphthalein Structure

There are three hexagonal structures and one pentagonal structure, two alcoholic groups, and one ketone group in the structure of Phenolphthalein. Also, the carbon, Hydrogen and Oxygen chains form the Phenolphthalein structure.

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Properties of Phenolphthalein

 

Synthesis of Phenolphthalein

Phenolphthalein can be synthesized by phthalic anhydride condensation with two phenol equivalents under acidic conditions. Adolf von Baeyer discovered it in 1871.

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Phenolphthalein Uses

1. In acid-base titrations, the popular use of phenolphthalein is as an indicator (phenolphthalein titration).

• To determine the concentration, titration is an experiment where a volume of a solution of known concentration is applied to a volume of another solution. Most titrations are acid-base neutralization reactions.

• Non-ionized forms of phenolphthalein are colourless. The protonated form of phenolphthalein in acidic solution is orange in colour. The deprotonated form of phenolphthalein in the basic solution is pink in colour.

• Phenolphthalein, although its ion is pink, is a weak acid and is colourless in solution. The equilibrium would shift if hydrogen ions (H⁺, as found in an acid) were applied to the pink solution, and the solution would be colourless. The phenolphthalein will be converted into its ion by adding hydroxide ions (OH^–, as found in bases) and the solution will turn pink.

• As a result of pH modifications, Phenolphthalein adopts at least four distinct stages in an aqueous solution. It occurs in the protonated form (HIn⁺) under highly acidic conditions, producing an orange colouration. The lactone type (HIn) is colourless in both highly acidic and slightly simple conditions. The familiar pink colour is given by the doubly deprotonated (In^2–) phenolate form (the anion form of phenol). Phenolphthalein is converted to its In(OH)₃ form in highly simple solutions, and its pink colour undergoes a very slow fading reaction and becomes completely colourless above 13.0 pH.

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Note: It also serves, along with methyl red, bromothymol blue, and thymol blue, as a part of the universal indicator.

 

2. Cement Carbonation: Cement naturally has a high pH as it forms calcium hydroxide when it reacts with water. In the atmosphere, concrete reacts with carbon dioxide and its pH is reduced to 8.5-9 pH. If phenolphthalein is applied to the cement undergoing carbonation, it remains colourless. Phenolphthalein turns pink when it’s applied to normal cement.

3. Phenolphthalein has been used as a laxative before.

4. Medical Uses:

Kastle–Meyer Test

In a test to classify substances believed to contain blood, widely known as the Kastle-Meyer test, a reduced form of phenolphthalein, phenolphthalein, which is colourless, is used. Through a swab or filter paper, a dry sample is obtained. A few drops of alcohol are dripped onto the sample, then a few drops of phenolphthalein, and finally a few drops of hydrogen peroxide. If the sample contains haemoglobin, and phenolphthalein is applied, it will turn pink immediately upon the peroxide addition.

 

A positive test means that the sample contains haemoglobin and is thus likely to contain blood. The presence of substances with catalytic activity similar to haemoglobin will result in a false positive. This test is not harmful to the specimen; it can be preserved and used in further experiments. Every species whose blood contains haemoglobin, including almost all vertebrates, has the same reaction to blood in this test; further research will be appropriate to determine if it came from a human being.

 

Harmful Effects of Phenolphthalein

Phenolphthalein is believed to be carcinogenic in nature. Facing concerns about its carcinogenicity, it is doubtful that the use of phenolphthalein as a laxative would induce ovarian cancer via SOCE (Calcium release-activated channel and  Structure), it has been found to inhibit human cellular calcium influx. This is accomplished by inhibiting thrombin and thapsigargin, two SOCE activators that increase free calcium intracellularly.

Phosphorylation is a chemical process in which a phosphoryl group (PO₃^2-) is added to an organic compound. In other words, phosphorylation meaning in chemistry is depicted as an organic process that involves the addition of a phosphorous group with an organic compound. For example, when phosphate is added to glucose, it becomes glucose monophosphate. In a similar manner, when phosphate is added to adenosine diphosphate it results in adenosine triphosphate. 

Phosphorylation plays a very important role in regulating protein function and transmitting various signals throughout the human body cell. Though it is predominantly observed in bacterial protein, it is considered more prevalent in eukaryotic cells. It has been observed at some point in time, one-third of the protein present in the human proteome are substrates of phosphorylation. Therefore, phosphoproteomics has evolved as a part of proteomics that focuses only on identifying and characterizing phosphorylated proteins. 

Other than this, phosphorylation helps in conserving much of the energy in food by the process of oxidation and makes it available to the cell. Even green plants use a process called photophosphorylation for converting the light energy it absorbs into chemical energy. This process is commonly known as photosynthesis.

Phosphorylation Reaction and Mechanism

Proteins often undergo a huge post-translational modification most of the times. Out of all the post-translational modification of proteins that happen, phosphorylation is the most important and is found almost everywhere. Of all the proteins that are available in the cell cytosol, 10% of them undergo phosphorylation. 

Phosphorylation reaction is one of the most widespread reactions that happen in human cells to phosphorylate the proteins that are present in the human proteome. The phosphorylation reaction that takes place in the cell is reversible in nature where catalysts such as kinases are used for the addition of the phosphoryl group and phosphatases catalyzes the removal of the phosphoryl group. 

In this reaction, ATP has the main function as it works as a phosphoryl donor or the phosphorylation reaction and acts as a reagent for hydrolysis of phosphoryl group in the dephosphorylation reaction. The entire reaction can be depicted as the hydrolysis reaction of ATP as the ΔG value is -12kcal / mol under cellular conditions and therefore, considered to be favourable for energy.

E + ATP → E―P + ADP, this is phosphorylation reaction 

E – P + H₂O →  P_i + E, this is dephosphorylation reaction

ATP + H₂O  →  P_i + ADP, this is the net result of above two reactions

From the above reactions, it is evident that phosphorylation is predominant in the post-translational modification that regulates protein functions in the body. Phosphorylation occurs at the end chain of three amino acids, tyrosine and threonine. The phosphate group (y-PO₃^2-) which is present at the terminal of universal phosphoryl group donor ATP, is attacked by a nucleophilic hydroxyl group (-OH) present in amino acid. This results in the transfer of the phosphate group to the amino side chain, and the entire reaction is facilitated by (Mg²⁺) ions. In order for the phosphoryl group to transfer easily to the nucleophilic hydroxyl group, magnesium ions bring down the threshold of phosphoryl transfer by chelating with γ- and 𝛽- phosphate. A large amount of free energy is released when the phosphate-phosphate bond in ATP is broken in order to form adenosine diphosphate ADP.

 

Glucose and Glycolysis

Glycolysis is a very important process in which the glucose is broken down into two molecules of pyruvate in many steps with the help of various enzymes initiating the reaction at several stages. Precisely the process of glycolysis is carried out in ten steps and phosphorylation plays a major part in attaining the main end product. Phosphorylation initiates the first step of the preparatory stage, that is, half glycolysis and the last step of the payoff phase, that is, second glycolysis. As glucose is a very small molecule, thus, it has the ability to diffuse out through the membrane of the cell. Now when the phosphorylation of glucose happens in the first stage of glycolysis, glucose gets converted into glucose-6-phosphate which is relatively a bigger molecule than glucose. Therefore, it is trapped inside the membrane which then becomes negatively charged. This entire reaction is initiated by an enzyme called hexokinase. In the third phase of glycolysis, phosphorylation takes place and it converts fructose-6-phosphate into fructose-6- bisphosphate. This reaction is catalysed by phosphofructokinase. While the phosphorylation in the first step is initiated by ATP, phosphorylation in the payoff stage is maintained by inorganic phosphate.

Protein Phosphorylation

Protein phosphorylation is one of the most abundant and widespread post-translational modifications that occur in eukaryotes. Phosphorylation primarily occurs in the side chains of serine, threonine and tyrosine through phosphoester bond formation. Its occurrence is also evident in histidine, lysine and arginine through phosphoramidate bonds and in aspartic acid and glutamic acid through mixed anhydride linkage. Phosphorylation widely happens on human proteins at multiple non-canonical amino acids that include motifs that comprisethe histidine, aspartate, glutamate, arginine and lysine. Histidine phosphorylation takes place in both 1,3- N atoms of the imidazole ring. Being one of the most important PMT’s, protein phosphorylation plays a very important role in regulating cardiovascular, gastrointestinal, immunity, behavioural as well as actions of neurological irregularities. In addition to this, protein phosphorylation can contribute to one of the most critical pathological conditions, cancer. Studies found that the proteins in the human body guarded by the human genome are capable of undergoing protein phosphorylation.

Methods of Detection

Since phosphorylation has a huge impact on the human biological system and genomes and has the capability to fight against many diseases, a lot of methods have been developed to analyze the phosphorylation of the protein. One of the most common methods used to analyze the dynamics of phosphorylation of the entire protein family is the phosphoproteomic process. Though the small scale protein phosphorylation is generally performed to study small proteins, many modern methods are developed to analyse the dynamics of protein phosphorylation. Those methods are immunodetection, mass spectroscopy, phosphoprotein or phosphopeptide enrichment and kinase activity assays.

Every home, every industry makes use of some of the other forms of the separation method. The separation method in simple terms is the process of segregation, where unwanted particles are separated from the essential parts. In this particular article, we shall be learning in detail about various physical separation methods. By the end of the discussion, students would be able to identify different methods and their significance.

 

Table of Content 

1. Filtration

2. Centrifugation

3. Magnetism

4. Evaporation

5. Distillation

What is a Mixture?

A mixture is a substance made by combining two or more different substances (elements or compounds), not necessarily in a definite ratio. In a mixture, the constituents do not combine chemically (no chemical reaction occurs). Since there is no chemical reaction involved, the constituents retain their original properties. In the formation of a mixture, there is no loss or gain of energy. We can easily separate the components of a mixture using physical methods.

Separation of the Constituents of a Mixture

A mixture is formed as a result of a physical change. Therefore, in order to separate the constituents of a mixture, certain physical methods or techniques can be employed by which a mixture can be separated back into its original components. These techniques are based on physical properties of the components such as densities, weight, size, etc.

For example: Let us take a mixture of sand and water. Sand and water have different physical properties due to which we can separate sand and water by separation methods. When sand is added to water, it settles down at the bottom of the container because sand is heavier than water and insoluble in water(heterogeneous mixture). So, we can separate the sand from the mixture by filtration. A filter paper will allow the water to pass through as filtrate. We will discuss some physical separation methods here.

1. Filtration

This is a very common separation technique, which is used for separating an insoluble solid from a liquid. In this process, the mixture is passed through a filter paper. The liquid which has passed through the filter is called filtrate and the solid which remains on the filter paper is called the residue.

For example: In our daily life, the filtration method is used, while preparing tea.  We use a sieve at home to separate tea leaves from the water. Tea is obtained as the filtrate through the sieve pores.

2. Centrifugation

Sometimes, the solid particles in a liquid are minute enough to pass through a filter paper. In such cases,  filtration cannot be used for separation. Such mixtures are separated by centrifugation. So, centrifugation is the process in which insoluble substances are separated from a liquid, in situations where filtration does not yield the desired result. Centrifugation depends on the shape, size, and density of particles, viscosity (thickness) of the liquid medium, and speed at which the centrifuge is rotated. This method of separation is used when very tiny solid particles are suspended in a liquid medium. The principle on which a centrifuge works is that the denser particles remain at the bottom while the lighter particles collect at the top due to centrifugal force. 

3. Magnetism

In this technique of separation, a  magnet is used to separate the magnetic components from a mixture. This method can only be used when the given mixture contains a magnetic component like iron, nickel, cobalt, etc. This process is widely used in waste management where the magnet is used to separate metal from discarded waste.              

4. Evaporation

This separation method is used to separate a soluble solid from a liquid. In this process, a mixture is heated until the solvent evaporates. The mixture should contain only one liquid component.

For example: In many parts of the world, salt is obtained from seawater by evaporation. Water evaporates due to the heat coming from the Sun. 

5. Distillation

This is an effective method of separation of two or more liquids. This process is based upon the difference in boiling points of the different components in the mixture that are being separated. In this process, the mixture is heated and boiled until it reaches its boiling point. Then the temperature is maintained until the significant liquid completely vaporizes. The most volatile component vaporizes at the lowest temperature. The vapor passes through a cooled tube(condenser). This condensed liquid is collected in a container. Simply, distillation is a process in which a mixture is heated. The component with the lowest boiling point evaporates first, then it is condensed and isolated.

For example, Alcohol is a liquid that is soluble in water. So, if we want to separate alcohol and water from a mixture, we will have to use the process of distillation. The mixture is kept in a distillation flask. As the heat is supplied, alcohol has a lower boiling point and will start forming vapors at 78°C. As these vapours will rise and enter the condenser, a supply of cold water cools the vapours to form alcohol droplets, which can then be collected in a container. The liquid left behind in the distillation flask will be water.

However, the method of distillation can also be used if we want to separate a soluble solid from a liquid and want to obtain both the liquid and the solid components. This is different from the case of evaporation because, in evaporation, we are able to obtain only the solid while the liquid component forms vapors and cannot be collected.

Key Learnings from the Chapter:

• When two or more substances combine together they take the form of a mixture. 

• To separate the constituents of a mixture some form of physical methods of separation are to be used

• There are five major separation methods

• In the filtration method, the mixture is passed through a filter paper, the liquid gets strained to leave behind suspended particles

• The centrifugation method is used to strain the tiny suspended particles which could not be captured by the filtration method

• The evaporation method is used to separate the solid particle from the liquid by heating

• Distillation also make use of heat to separate the particles

The chemical compounds that are held together by polar covalent bonds are known as polar compounds. The word ‘polar compound’ can be defined as a chemical species consisting of two or more atoms that are kept together due to the unequal sharing of electrons by covalent bonds that are polar in nature. The differences in the electronegativities of the bonded atoms may cause the bond pair of electrons to move closer to the more electronegative atom when two atoms are bound together by a covalent bond.

Overview of Polar Compounds

It is important to remember that polar compounds are different from ionic compounds. Ionic compounds are held together by ionic bonds that occur between ions due to electrostatic forces. In such situations, to form a cation, one of the atoms loses an electron and another atom receives an electron to form an anion. In polar compounds, there are two chemical species sharing the electron pair. However, due to the variations in electronegativity of the two chemically bound species, the electron pair is exchanged in an unequal way.

No compound is a hundred percent ionic nor covalent. Even when the two hydrogen atoms combine by covalent bond, they possess some ionic character.

Heteronuclear molecules are said to be polar compounds because the electron pair sift towards the more electronegative atom resulting in the polarity of bonds. Due to this polarity, the molecule possesses the dipole moment. The dipole moment is defined as the product of the magnitude of charge and distance of separation of charges. It is denoted by ‘d.’ The dipole moment is expressed in Debye.

μ = q x d

Examples of Polar Molecule

Here are some examples of polar compounds-

Water

Water is a polar compound since the water molecule’s covalent bonds between hydrogen and oxygen are polar in nature. Owing to the variations in the electronegativity of hydrogen and oxygen, the bond polarity of the hydrogen-oxygen bond occurs. It draws the bond pair of electrons closer to itself, as oxygen is more electronegative than hydrogen. This allows a partial negative charge to be produced by the oxygen atom and a partial positive charge to be developed by the hydrogen atom.

Hydrogen Fluoride

As the covalent bond between hydrogen and fluorine in this compound has a polar nature, hydrogen fluoride is a polar compound. Since fluorine is much more electronegative than hydrogen, it draws the electron bond pair closer to itself and, in the process produces a partial negative charge. The hydrogen atom, on the other hand, produces a partial positive charge (since the bond pair of electrons is placed quite far away from the nucleus of the hydrogen atom).

Ethanol

A polar covalent bond between the terminal carbon and the hydroxyl group occurs in the ethanol molecule. As oxygen is more electronegative than carbon, this carbon-oxygen bond is polar in nature, allowing it to move the bond pair of electrons closer to itself and gain a partial negative charge in the process. Since the electron pair is located relatively far away from its nucleus, the carbon atom gains a partial positive charge.

Differentiation of Polar Compounds from the Non-Polar compounds

Let us look at the differentiation of the polar compounds from the non-polar ones.

Polar compounds have atoms with differing electronegativity, which is usually quite large. As a result, the atom that is more electronegative than the other tends to draw the linked electron (in a covalent bond) toward itself. This results in a loss on more electronegative ones and addition on less electronegative ones with less charges.

The electronegativity of an atom is related to its diameter. Because the nucleus is further away from the outer valence electron shell or bonded electrons, the larger the diameter, the less electronegative it gets. This also explains why group 7 tends to undergo more ionic reactions than covalent reactions (larger diameter loss easily than holding on).

Because the atoms in non-polar are of relatively identical size/diameter, their electronegativity is more or less equal, bound electrons sit between them (equal distance apart).

Non-polar chemicals are soluble in non-polar compounds, such as butane in octane/gasoline, and polar compounds are soluble in polar compounds, such as ethanol in water. 

Did You Know?

There are two important factors to determine the polarity of bonds-

To determine the polarity of bonds, check the electronegativity of an atom. If the difference between electronegativities is less than or equal to  0.4 then the compound is said to be non-polar and if the difference between electronegativities lies between 0.5 to 1.7 the compound is said to be polar.

Molecules with bent and trigonal pyramidal shapes are always polar.

Polymorphism definition in chemistry states that polymorphism is the condition in which a solid chemical substance exists in more than one crystalline form. When given a set of building blocks, you can make the various structures with the same blocks. Now, think of the blocks as molecules and the structures as crystals. A crystal of a solid is formed when the molecules are arranged symmetrically in a repeating pattern. However, for a combination of drugs, there can be more than one repeating pattern in which they can arrange themselves. This leads to the condition called polymorphism in chemistry, where the same chemical compound exists in different crystalline forms.  

 

Polymorphism: An Overview

In materials science, polymorphism refers to the existence of solid material in several forms or crystal structures. Isomerism is a type of polymorphism. Polymorphism is a phenomenon that can occur in any crystalline substance. Polymorphism in chemical elements is defined by allotropy. Agrochemicals, dyestuffs, medicines, foods, pigments, and explosives all benefit from polymorphism.

A polymorphic transition is a reversible transition, according to the International Union of Pure and Applied Chemistry. It’s a reversible transition from one solid crystalline phase to another with the same chemical makeup but a different crystal structure at a specific temperature and pressure. Dimorphic materials have two polymorphs, trimorphic materials have three polymorphs, and so on.

Which Properties can Differ Due to Polymorphism? 

The various polymorphs of a compound possess distinct physical and sometimes chemical properties, although the solutions and vapours appear identical. Various polymorphs of a substance may exhibit substantial differences in physical properties such as melting point, colour, hardness, density, electrical conductivity, hygroscopicity, latent heat of fusion, solubility, and dissolution rate, as well as variance in chemical reactivity. 

 

Types of Polymorphism

It is quite common for the molecules of a substance to rearrange themselves in different forms, to make polymorphism a common occurrence. Considering the stability of the solid crystals concerning temperature and pressure, we can classify polymorphism into two broad categories. 

 

Polymorphism is a regular occurrence in which the molecules of a substance rearrange themselves into new forms. Polymorphism can be divided into two groups based on the stability of solid crystals at different temperatures and pressures.

1. Mono-tropic Polymorphism: In the mono-tropic system of polymorphism, only one polymorph is stable for all acceptable temperatures. The compound metolazone exhibits this type of polymorphism. 

Only one polymorph is stable at all tolerable temperatures in the mono-tropic system of polymorphism. This polymorphism can be found in the chemical metolazone.

2. Enantiotropic Polymorphism: In the enantiotropic system of polymorphism, there are different polymorphs, and each polymorph is stable under a specific range of temperature. So, one polymorph can be stable at a low-temperature range; one can be stable at a high-temperature range and so on. The compounds carbamazepine and acetazolamide exhibit this type of polymorphism. 

There are multiple polymorphs in the enantiotropic system of polymorphism, and each polymorph is stable across a certain temperature range. As a result, one polymorph may be stable at low temperatures, while another may be stable at high temperatures, and so on. This polymorphism can be seen in the drugs acetazolamide and carbamazepine.

Relationship Between Polymorphs and Solvates

A solvate is an aggregate constituting a solute ion or a molecule along with one or more solvent molecules.

• Thermodynamically, when the most stable anhydrous polymorph ceases to be the most stable, it converts into a solvate in the presence of the right amount of solvent. 

• The thermodynamically most stable solvate is not necessarily the lowest level of a solvate. 

• A particular solvent can have polymorphs, for example, Nedocromil Zinc 

Application of Polymorphism 

Polymorphism is mainly useful in the pharmaceutical field for drug development. The structure of the solid crystal is essential to determine the effectiveness of the drug and the effects it can have on the body. Owing to variations in the solubility of polymorphs, one polymorph can be more therapeutically successful than another polymorph of the same product. In many cases, a particular drug receives regulatory approval for only one of its polymorphs. 

 

Polymorphism is extremely useful in the pharmaceutical industry for drug development. The structure of the solid crystal is critical in determining the drug’s effectiveness and potential side effects. Due to differences in polymorph solubility, one polymorph of the same substance and use can be more therapeutically successful than another. In many circumstances, a drug’s regulatory approval is limited to just one of its polymorphs.

Polymorphism in Pharmacy

• Paracetamol powder has poor compression properties; this poses difficulties in making tablets, so a new, more compressible polymorph of paracetamol has been found. 

• Cortisone acetate is found in at least five separate polymorphs, four of which are soluble in water and transform to a stable shape. 

• Carbamazepine beta-polymorph was produced from solvents with a high dielectric constant ex aliphatic alcohol, while alpha polymorphic solvents such as carbon tetrachloride were crystallized from low dielectric constants. 

The Peculiar Case of Ritonavir

Ritonavir is an antiviral drug. One of its polymorphs was virtually inactive compared to the alternative polymorph. Later, it was discovered that the inactive polymorph transformed the active polymorph into the inactive form upon contact. This was because of its lower energy and greater stability making spontaneous rearrangement energetically desirable. Just a few particles of the lower energy polymorph could convert massive amounts of ritonavir into the clinically worthless inactive polymorph, causing major production problems that were finally solved by administering the medicine through gel caps and tablets instead of the original capsules.

 

Ritonavir is a type of antiviral medication. In comparison to the alternate polymorph, one of the polymorphs was virtually inert. When the active polymorph comes into contact with the inactive polymorph, the active polymorph transforms into the inactive form. It was chosen because of its lower energy and greater stability, making spontaneous rearrangement attractive from an energetic standpoint. Massive amounts of ritonavir could be converted into the therapeutically useless inactive polymorph with just a few particles of the lower energy polymorph. The useless inactive polymorph wreaks havoc on production. These issues were finally resolved by using gel caps and tablets instead of capsules to dispense the medicat
ion.