Category: Chemistry Notes PPT

A drug is any chemical substance that brings about changes in the functioning of living organisms. Pharmacology is the science that studies and deals with drugs in medicines and their mechanism of action, physical and chemical properties, metabolism toxicity and therapeutics. Principles of drug action and different types of drugs are used in the treatment and prevention of diseases in human beings

A branch of medicine and pharmaceutical sciences concerned with drugs or the aftereffect of medicine, where a drug may be defined as any artificial, natural, or endogenous molecule which exerts a physiological or biochemical effect on the cell, tissue, or organ of the body. To be more specific we can say that it is the study of the interactions that occur between a living organism and chemicals that affect biochemical processes. Substances possessing medicinal properties are considered pharmaceuticals.

Types of Pharmacology

Pharmacology has the following Branches:

1. Pharmacokinetics: It describes what our body does to a drug, referring to the movement of the drug in our body, through the body and out of the body. This process usually occurs in 4 phases in pharmacokinetics. 

• Absorption

• Distribution

• Metabolism 

• Excretion 

Sometimes known by the acronym ‘ADME’.

2. Pharmacodynamics: It is just the opposite of what pharmacokinetics is, it describes what a drug does to our body or how our body responds to the drug. 

The study of the physiological, molecular and biochemical effects of drugs on the human body involves the study of post-receptor effects, chemical interactions and receptor bindings. Together pharmacokinetics and pharmacodynamics build a dose-response relationship.

Types of Drugs and Their Uses

Medicinal drugs are chemical drugs divided into different groups or classes based on their uses, chemical structure or mode of action. These classification systems are sometimes confusing as one drug type may be included in more than one class. 

Antimicrobial Drugs: Drugs are used for the prevention or treatment of diseases caused by microbes like bacteria, fungi, protozoa, viruses or helminths. They contain chemical substances which kill or reduce the metabolic products produced by the microorganisms. Antibiotics come under the category of antimicrobial drugs. Example- penicillin.

Immunosuppressants: Immunosuppressants are a group of medicines used to block the immune response and are generally administered to patients who have undergone organ transplantation or are suffering from an autoimmune disease. Some of the common immunosuppressants are drugs that contain polyclonal antibodies, monoclonal antibodies, glucocorticoids, etc.

Drugs that Affect Blood: There are drugs that have to activate or inhibit enzymes that are involved in the regulation of blood clotting within the blood vessels. These drugs are administered in conditions like atherosclerosis or any kind of blockage in arteries occurring in the blood flow. There are various drugs like anticoagulants, antiplatelet drugs and fibrinolytic drugs which are involved in controlling the coagulation process.

Cardiovascular Drugs: These affect the functioning of the heart and blood vessels. They are administered for cardiovascular diseases like hypertension, and atherosclerosis. These drugs also affect the functioning of the heart muscles, frequency and regularity of heartbeat, etc. 

Endocrine Drugs: Drugs that are used to treat endocrine abnormalities. Their functioning includes changes in the regulation of the hormonal axis, effects on hormonal transport, as well as similar changes to counter-regulatory hormone systems. Endocrine drugs are used for the treatment of thyroid, Addison disease, etc.

Reproductive Drugs: These affect the functioning of our reproductive system. These drugs are used for treating reproductive diseases. 

Central nervous system drugs: These affect the functioning of the central nervous system. These drugs are administered in order to produce changes in behaviour, a physical sensation or mental state. Local anaesthetics, on the other hand, induce a loss of sensation in just one area of the body by blocking conduction in nerves at and near the injection site.

Digestive System Drugs:  These groups of drugs act on the digestive system by affecting the actions of the involuntary muscle (motility) and thus altering movement or also by altering the secretion of digestive juices or gastric emptying. Examples of major groups of digestive drugs include antidiarrheal drugs, laxatives, antiemetics, emetics, proton pump inhibitors, and antacids.

Dermatologic Drugs: Topical application of drugs provides a direct, localized effect on a specific area of the skin. When these drugs are applied to the skin, they may be dissolved in a variety of formulations, ranging from simple solutions to greasy ointments. These medications can relieve itching, exert a constricting or astringent action on the pores, or dissolve or remove the epidermal layers. The skin can be affected by other means like photosensitizing drugs, and pigmenting agents (psoralens).

The chemical drugs list can be endless. There are numerous drugs for various diseases. These drugs are of vital importance to humankind. The knowledge of pharmacology and drugs is also indispensable to medical science. It helps create wonders in the human body and soothe numerous ailments. 

Did You Know?

Drugs are often abused by people. Adolescence is a period when a lot of people indulge in drug abuse and dependency. This can be due to experimentation, curiosity or even depression. This can cause serious issues which lead to severe consequences and even death. Drugs abused are opioids, cannabinoids, coca alkaloids, etc. These when taken in overdose can cause life-threatening damages.

We are completely aware that an organic compound is made up of carbons and hydrogen atoms. But unsaturated carbons state that adjacent carbon atoms have formed either a double or triple bond with each other. To make them saturated, we need to add more hydrogen atoms to them.

These unsaturated ones can be in the form of straight-chain or branched chains or aromatic compounds. The ones which have at least one double bond between carbon atoms are known as alkenes. But if there is at least one triple bond between carbons in an organic compound, they are alkynes. Below you will understand different types, examples, and the uses of Unsaturated Hydrocarbons in detail.

What are Hydrocarbons? Give Examples.

An organic compound is a hydrocarbon when it contains carbon and hydrogen atoms in it. These can be either saturated or unsaturated. Saturated ones are those having a single bond between two carbon atoms or with a hydrogen atom. Unsaturated ones are those which have either a double or triple bond with two adjacent carbon atoms.

Some basic saturated hydrocarbon examples are methane and ethane. Unsaturated Hydrocarbon examples are Ethene and Ethyne.

What are Different Types of Unsaturated Carbon Compounds?

According to the basic unsaturated hydrocarbon definition, there are three different types. These are:

The classification is based upon the type of carbon-carbon bond in the compound. Also, it is defined by its basic structure.

• If there is at least one double bond between two adjacent carbon atoms in a hydrocarbon, those are alkenes or olefins. Ethene is an example of such a type given by [C_{2}H_{4}]. These will have only one double bond with no functional groups. The basic formula is given by [C_{2}H_{2n}].

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• In Alkynes, there is at least one triple bond between two adjacent carbon atoms. An example of such a kind is acetylene given by [C_{2}H_{2}]. The basic unsaturated hydrocarbon formula for alkynes is given by [C_{2}H_{2n – 2}].

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If you want to check if a particular hydrocarbon is unsaturated, you can add bromine water to it. In case water turns decolourised, it is unsaturated. If it forms a precipitate, then it is phenol. Also, benzene is the one that will not decolorize bromine water. 

What are the Different Uses of Unsaturated Carbon Compounds?

Uses of compounds listed among unsaturated category are:

• It is the usual case of ripening fruits with the help of alkenes.

• In chemistry, we include unsaturated carbons to synthesize various compounds. They are usually used as monomers in such areas.

• Mustard gas is prepared with the help of alkenes which is often required for chemical warfare. It is poisonous.

• Acetylene is the fuel used inside a torch that we generally use in a home project.

• Unsaturated compounds are generally used in the manufacturing of plastics.

• Alkenes are used in industries for synthesizing fuel, detergent, plastic, and alcohol.

• The use of Polystyrene is generally for disposable cups, egg cartons, and other convenient products.

Physical Properties of Unsaturated Carbon

• As talked about above, unsaturated compounds have either one double or triple bond. These are generally given by the formula [C_{2}H_{2n}] and [C_{2}H_{2n – 2}].

• To make unsaturated as saturated compounds, we need to add hydrogen atoms to them. This will form more carbon and hydrogen bonds.

• The carbon-carbon bond formed in a double bond of carbons will form 120 degree angles.

• The carbon-carbon bond formed in the triple bond of carbons will form 180 degree angles.

• Unsaturated compounds get through different reactions, including combustion reactions, addition reactions, oxidation reactions performed by alkenes, polymerization of alkenes.

• Combustion reactions include the formation of carbon dioxide and water.

• The addition reaction is either symmetrical or unsymmetrical.

• Oxidation Reactions include either addition of oxygen in a molecule or the removal of hydrogen from a molecule.

• If reactions are conducted under pressure at a particular temperature with the help of a catalyst, these are polymerization reactions. The molecules produced are polymers.

• The most common example of aromatic compounds universally considered is benzene. It forms 120 degrees between constituent carbon atoms.

Saturated Vs Unsaturated Hydrocarbons:

Both the compounds are organic compounds i.e, made up of hydrogen and carbon atoms. The major difference between both is the type of bonds they form. Saturated hydrocarbons have one covalent carbon bond, for example, methane, propane, and butane are some of the saturated hydrocarbons as they have a single carbon covalent bond and unsaturated hydrocarbons on the other hand have either a double covalent carbon bond or a triple covalent carbon bond. 

Unsaturated hydrocarbons are further divided into alkenes and alkynes based on the number of covalent bonds that the carbon atoms form. The hydrogenation reaction is the test used to figure out whether a compound is a saturated hydrocarbon or an unsaturated hydrocarbon. Hydrogenation is a type of reduction reaction where a hydrogen atom is added to a particular compound to know whether it is saturated or unsaturated. When the hydrogen atom is added to a compound it gets saturated and it tells us the previous stage of the compound. 

The above article has discussed different properties, types, and uses of unsaturated hydrocarbons. Surely, this will help you understand and clarify your concepts on the topic.

Science is a beautiful subject that studies the Universe with experimentation and trial and error. This deals in every area of the universe. For students, this subject deals with three main categories. This includes physics, Chemistry and Biology streams of Science. In this article, Students will learn a topic from the Chemistry stream, that is, Amines.

Chemistry is the branch of Science that deals with substances, their chemical properties and reactions. Apart from the educational importance of this subject, Chemistry also actively participates in the everyday life of human beings. This includes examples of branches like health, energy, drugs, metals, textiles, paper, cosmetics, cleaners etc.

What are Amines?

Amines are one of the most prolific members of the nitrogen-based organic compounds which also constitutes the indirect source of ammonia. Amines are derived by replacing one or more Hydrogen molecules from ammonia with one or the other alkyl.  As a derivative of ammonia, amines serve several practical purposes across different industries. Be it the agrochemicals industries or the pharmaceuticals markets, amines are integral to the core as well as the by-products of these industries. There are many uses of amines in our everyday lives. But, before we delve into the uses of amines, let’s understand what amines are and familiarise ourselves with their structural properties. 

 

Amines Structure

An organic compound, belonging to the functional group comprising a basic nitrogen atom with a lone pair, are called amines. Amines compounds mainly form hydrogen bonds as a consequence of which they are highly soluble in water and have high boiling points. Amines are compounds of the nitrogen group which are attached to a carbonyl within the structure. As such, Amines have the following structure:

 

 R-CO-NR’R”

 

This salient structure of amines is to a large extent responsible for the multifaceted uses of amines. Some groups of amines also form an aromatic structure which in turn reduces their alkalinity. In general, the compounds of the amine groups are less reactive than the other organic compounds by virtue of their electron donating attribute. Fundamentally, the structure of amines comprise trivalent nitrogen atoms with an unshared pair of electrons. Depending on their bonding environments, amines can further be categorised in three ways. When one of the three hydrogen atoms are replaced by an alkyl or an aromatic element, the amines are called primary amines. When two of the hydrogen atoms are substituted and one hydrogen atom bonded with a nitrogen atom, such amines are called secondary amines. Finally, tertiary amines are those whose hydrogen atoms have been replaced by an organic substitute. Secondary and tertiary amines can further be divided into cyclic amines when the compound forms a ring structure. If the substituent alkyls belong to the same group, then such amines are called simple and if it is constituent of more than one group, then they are called mixed amines. The structure and propensity to replace an electron make it appropriate for a wide range of uses of amines. 

 

Physical Properties of Amines

The uses of anime majorly stem from the structure as well as the properties of amines. To gauge the extent of the uses of amines, let us first assess the physical properties of amines. Being hydrogen-based compounds, amines have elevated boiling points and a substantial degree of solubility in water. However, if there are more carbon atoms present in an amine compound, then the solubility in water will decrease. Amine compounds can exist in different forms depending on the number of carbon atoms present. Amines with a lesser number of carbon atoms are typically gases and have a fishy odour while amines with upto three carbon atoms are in liquid form. If an amine compound has more than three carbon atoms, it will be available in the solid-state. Mostly, amines are colourless but might obtain some colour when subject to atmospheric oxidation. 

 

Chemical Properties of Amines

The most prominent chemical properties of amines include their basic nature. The basicity of the amines increases with the increase of the alkyl groups. Amines also undergo several chemical reactions through processes like alkylation, acylation, carbylamine reactions, electrophilic substitution among others. As a source of ammonia, amines also react with nitrous acid and aryl sulfonyl chloride, the end product is mostly a yellowish oil-like substance. 

 

Electrophilic Substitution

 

Now that we know the structure of amines, the physical properties of amines as well as the chemical reactions it enters into, let us delve into certain examples of amines and their uses. 

 

Uses of Amines in Daily Life

Some Uses are:

• One of the most common uses of amines is in gas treatment, where amines are used to remove CO2 from combustion gases. 

• Amines are a key ingredient in the preparation of material dyes. 

• In the textile and garments industry, amines are commonly used in the preparation of azo dyes which in turn are critical for treatment of materials like leather and nylon. 

• It is also a rich source for solubilizing herbicides and used as emulsifiers. 

• In the chemical processing industries, amines are used as inhibitors of corrosion in boilers and lubricating oils. 

• Another unique use of amines is as developing agents of photographs. 

 

Uses of Amines in Pharmacy

Some Pharmaceutical Uses are: 

• Amines are frequently used in morphine and Demerol which are popular pain killers. 

• Amines are also used as solvents for antihistamine diphenhydramine which are used in Benadryl syrups. 

• Novocaine is one drug used as an anaesthetic which is hugely dependent on amines. 

• Amines are important sources of amino acids which regulate the vitamin levels in our bodies.

• Amines are useful stimulants for neurotransmitters like serotonin for our bodies.

Glycerol is a naturally occurring chemical and is used as a medicine in the treatment of burns and wounds. It is a clear colourless, odourless, sweet-tasting liquid that is viscous in nature and belongs to the alcohol family of organic compounds. It is generally obtained from plant and animal sources where it occurs in triglycerides. 

Glycerol is present in a small amount in human tissues in the form of trivalent alcohol. It is a volatile liquid and if it is left outside in contact with the environment it will vaporize even at room temperature. Glycerol is biodegradable and when exposed to the environment it will distribute itself in air, soil, or sediment. 

Along with these advantages, there are some disadvantages of glycerol, It can cause headaches, dizziness, nausea when taken directly. It can also cause a skin rash, redness, or burns to the skin if applied directly. It can cause serious damage to RBCs if injected. Therefore, the use of glycerol should be done under medical supervision only.

Glycerol Structure

The molecular formula of Glycerol is: C3H8O3

It is a trifunctional compound i.e. three alcohol groups are present on three carbon atoms and its IUPAC name is 1,2,3− propane triol.

Density: 1.26 g/cm³

Molar mass: 92.09382 g/mol

Boiling point: 290 °C

Glycerol Uses

Medical Uses:

• Glycerol is commonly used to relieve occasional constipation, improving hydration and performance in athletes, and improving skin conditions. 

• It can be used for the treatment of wounds and types of burns.  it is to be remembered that glycerol cannot be used for the treatment of third-degree burns. 

• Another important application of glycerol is in blood banks, where the compound is employed for the preservation of RBC before they are frozen for storage.

• Using a hair lotion containing glycerol 3 times per week can reduce dandruff by a small amount and moisturize the scalp. It is mostly used in glycerine soap.

• It is also used in shaving creams and eye drops for a similar purpose.

• Applying a product that contains glycerol to the skin can reduce the thickness of scales and itching in people with xerosis.

Other Uses of Glycerol:

• In the food industry, glycerol is used in order to retain moisture.

• A mixture of water and glycerol can be used to preserve the leaves of certain plants. 

• Athletes use glycerol to keep themselves away from becoming dehydrated.

• It is widely used as a raw material in the production of nitroglycerin.

• It is used as softening agents in baked goods, plasticizers in shortening, and stabilizers in ice cream.

• Glycerol is also used commonly in the film industry during the filming where water is involved mostly. In those situations, glycerol helps stop the areas from rapidly drying out.

• It is used in making many modern protective coatings like automotive enamels and exterior house paints.

Did You Know?

Glycerol and glycerin are two different solutions that have the same chemical compound but their nomenclature is different.

Glycerin is the commercial name of glycerol that contains 95% of glycerol. Glycerin cannot be used interchangeably with glycerol. Glycerin is a less pure form of glycerol. Glycerin is widely used in cosmetics, other than fragrances it is the most used product in the cosmetic industry. There are numerous products that include glycerin in them, especially in moisturizers and lotions. The pure form of glycerin is readily available in the market and people purchase it for use directly.

Petroleum i.e. crude oil is a naturally occurring liquid that is refined to prepare products like gasoline i.e. petrol, diesel fuel, jet fuel, home heating oil, lubricating oil, wax, asphalt, and many other useful products. The word petroleum originates from Latin, where “petra” means rock and “oleum” means oil. Petroleum also includes natural gas which has similar chemistry to crude oil. Transportation and power generation are the two major uses of petroleum. Chemicals obtained from the refining of crude oil and the processing of natural gas are used by the petrochemical industry to produce petrochemicals like synthetic rubber, fertilizers, plastic, latex paints, drugs, synthetic fibres, and explosives.

 

Properties of Petroleum

Crude oil can appear very fluid, volatile liquids and also viscous, semisolid materials. It is usually black or black with a greenish tinge in colour. Sometimes it can be reddish, greenish-yellow, light yellow, or transparent. Natural gas is a colourless and odourless gas.

Petroleum majorly contains alkanes and also cyclohexanes, aromatic hydrocarbons and more complex hydrocarbons such as asphaltenes. Carbon and hydrogen are the two basic constituent elements of petroleum. Crude oils vary greatly in their chemical composition due to the combination of the above elements in various complex ways. 

The properties of petroleum, such as viscosity, density, boiling point, and colour may vary extensively.  Heavier fractions like asphaltene contain greater metal concentration than saturated and aromatic fractions. Nitrogen and sulfur can be present in traces in light petroleum with an increase for heavier or extra-heavy crude oil.

 

The Basic Composition of Petroleum

 

What is Petroleum Used For?

Transportation: To date, petroleum is the basic source of energy used in transportation. Petroleum accounts for two-thirds of the total transportation fuel globally. Gasoline/petrol, diesel, liquefied petroleum gas (LPG), jet fuel, and marine fuel are the major transportation fuels obtained from petroleum. Cars, motorcycles, light trucks, buses, trains, boats and ships use gasoline or diesel. Jet aeroplanes and some types of helicopters often use kerosene.

Power Generation: A thermal power plant uses petroleum for electricity generation. Although coal is the major source of electricity generation, petroleum also accounts for significant power generation that eventually results in serious environmental pollution. 

Apart from these two uses of petroleum, the fuel has other industrial applications too. 

These are:

Lubricants: Almost all industries use lubricants for the proper functioning of machinery. Lubricants reduce friction in vehicles and industrial machines. However, they are even used in cooking, bio-applications on humans, ultrasound and medical examinations. 

Pharmaceuticals: Certain by-products like mineral oil and petrolatum are used in the manufacture of topical medicines. The complex organic molecules used in pharmaceuticals are linked to simple organic molecules of petroleum byproducts.

Agriculture: Ammonia, which is a source of nitrogen in agricultural fertilizers, is manufactured from petroleum using Haber’s process. Moreover, a lot of pesticides are produced from petroleum. Machinery for ploughing etc also works on petroleum. 

Chemical Industry: The raw materials of many chemical companies are by-products of a petroleum refinery. Chemical fertilizers, synthetic fibres, insecticides, synthetic rubber, nylon, plastics, pesticides, perfumes, dyes, paints etc are the significant products produced using the major by-products like naphtha, grease, petroleum jelly, wax, butadiene etc.

Domestic uses: Household products like detergents, vaseline, wax etc are by-products derived from petroleum. Kerosene is used in many countries for cooking, lighting and other domestic purposes.  

 

Different Types of Petroleum Products and their Applications

Let us look into the examples of petroleum products obtained from petroleum:-

Fuels

• Gasoline

• Kerosene

• Liquefied natural gas

• Liquefied petroleum gas

• Butane

• Diesel fuel

• Fuel oil

• Propane

Other Products

• Paraffin wax

• Petroleum jelly

• Petroleum wax

• Microcrystalline wax

• Napalm

• Naphtha

• Naphthalene

• Refined asphalt

• Refined bitumen

Fractional distillation column of Crude oil

 

Some Petroleum Products and their Uses

Gases

Gaseous products obtained from the refinery are hydrogen, fuel gas,ethane, propane, and butane. Propane and butane are collectively known as liquefied petroleum gas (LPG), which is a portable and suitable fuel for light industrial use and domestic heating (cooking).

Gasoline

Gasoline uses include application in internal combustion engines, commonly used in private and commercial vehicles.

Diesel

It is commonly used in trucks, buses and public transport, locomotives, farm and heavy equipment. Diesel has greater energy and power density than gasoline.

Kerosene

It is used extensively globally in cooking and space heating. It is also the basic fuel for modern jet engines. 

Fuel oil

It can be used as a power source of lamps, heaters, stoves, engines and lanterns typically at home in furnaces and boilers. The machinery of farming, mining or quarrying machinery or even bunkering ships uses fuel oil.

Other Petroleum Products

• Naphtha is used to manufacture solvents for paints, cosmetics, commercial dry cleaning etc. Paper manufacture and foodstuffs use wax.

• Asphaltic bitumen is employed in the construction of roads and airfields and the manufacture of roofing felts, waterproof papers, pipeline coatings, and electrical insulation. 

• Decomposing liquid hydrocarbon fractions make carbon black which is compounded with rubber in tire manufacture and used in printing inks and lacquers.

 

Did you Know?

One of the ancient civilizations, the Sumerians, discovered petroleum on the banks of the River Euphrates and used it for various purposes like road-building and waterproofing.

Petroleum is a naturally occurring, dark brown to a black mixture of hydrocarbons that can be refined into various types of fuels. The word petroleum comes from Latin and means “rock oil.” Petroleum has many uses including providing light in kerosene lamps, lubricating machinery with motor oil, powering cars with gasoline or diesel fuel, and heating homes with home heating oil. It is also used as the raw material for many chemical products such as solvents (e.g., paint thinner), brake fluid, asphalt pavement sealer, and roofing tar among others.

Petroleum is an Important Resource and Applied in Various Fields

• It is a valuable source of energy

• Petroleum is used to produce about 40% of the world’s electricity.

• It is also used as fuel for transportation. About two-thirds of the oil that is consumed in the United States is used for transportation, including cars, trucks, trains, planes, and boats.

• Petroleum can be turned into many different types of products such as plastics, fertilizers, and pharmaceuticals.

• It can also be burned to create heat or steam which can be used to generate electricity.

• Petroleum is also used to make many types of products including paints, dyes, detergents, and cosmetics.

• Petroleum is nonrenewable, which means that it cannot be replaced once it is used.

• Petroleum is a fossil fuel, which means that it comes from the remains of plants and animals that lived long ago.

Here are Some Tips to Study Petroleum

• Know the Composition– There are many kinds of petroleum such as crude oil, natural gas, and bitumen. It is important to know the different types and their compositions. So, it would be easy for you to study and research petroleum.

• Try and Understand the Steps Involved– When studying petroleum, try and understand the steps involved. This way, it will be easier for you to memorize facts about this topic.

• Know how it is Formed– You should also try to know how petroleum is formed. This way, you would be able to study this topic easily and in an organized manner.

• Create your own Study Guide– Petroleum can be a difficult topic to study. However, if you create your own study guide, it will make the process much easier for you. This guide should include all of the important topics that you need to know about petroleum.

• Start Learning each and every Aspect– When studying petroleum, you should start learning every little aspect of this topic. This way, it would be easier for you to study and memorize everything about this subject.

Valency is the number of atoms of a particular element that is combined with one atom of another element to form a molecule. Valency is also known as molecular weight. Valency is a measure of the combining power of an atom. The valency of an element is determined by the number of electrons in its outermost shell. The valency of an element can be increased either by gaining or losing electrons.

The Valence, or known as valency, in Chemistry, is the characteristics of an element that indicates the number of other atoms with which an atom of a particular element can form a covalent bond. Introduced in 1868, the term is used for the expression of both the possibility of combination of an element in general and the numerical value of the power of combination. Thus valence meaning is the number of electrons as most of the bonds are formed by the exchange of the valence electrons. The valence electrons determine the valency meaning in Chemistry and define what is valences in Chemistry.

Importance of Valency

The valency of an element is important because it determines how strong the bond between the atoms will be. The higher the valency, the stronger the bond. This is why elements with a high valency are often used in chemical reactions – they form strong bonds with other atoms.

Valency is also an important concept in chemistry because it helps us understand how atoms join together to form molecules. By understanding valency, we can better predict how chemicals will react with each other. This makes it easier to create new compounds for use in various industries. Valency is a fundamental concept that helps us understand the world around us.

Valency is an important measure of the combining power of atoms. The valency of an atom is determined by the number of electrons in its outermost shell. The valency of an element can be increased either by gaining or losing electrons. Valency is important because it gives us information about how atoms combine and why certain chemicals react the way they do. Valency also helps us predict the properties of new compounds that we create. Valence is fundamental to chemistry!

A Brief Account of Valence Chemistry

The explanation and the systematization of the concept of valence or valency was one of the major challenges for 19th-century chemists. As there was no satisfactory theory for the cause of valency, most of the efforts were done on making empirical rules for the determination of the valencies of the elements. The characteristic valence of elements was measured in terms of the number of atoms of hydrogen with which an atom of the element can merge or that it can replace in a compound. It later was quite evident, however, that the valencies of many of the elements varied in different compounds. 

 

The first great step in the development of a satisfactory explanation of valence and chemical combination was made by the American chemist G. N. Lewis in 1916 with the identification of the chemical bond present in the organic compounds as a pair of electrons was held jointly by two atoms which were holding them together. In the same year, the nature of the chemical bond between electrically charged atoms, or also known as ions, was discussed by the German physicist W. Kossel. 

 

The valence theory was reformulated and described incorporating electronic structures and interatomic forces after significant development in the field of electronic theory of periodicity of elements. Due to this several new concepts were introduced which included ionic valence, covalence, oxidation number, coordination number and metallic valence which also explain the different modes of atomic interactions. 

Define Valence and Valency

Most of the definitions in Chemistry are defined by IUPAC. Hence, the definitions in valence chemistry are also given by IUPAC. As per the IUPAC valence meaning is defined as the maximum number of single valence atoms that can possibly merge with an atom of the particular element under study, or with a fragment, or for which an atom of this element can be substituted.

 

Another description used to define valence in modern times is – The number of possible hydrogen atoms that can merge with an element in a binary hydride or twice the number of oxygen atoms that combine with an element in its oxide or oxides forms. This definition differs from the IUPAC definition as an element can be said to have more than one valence possible.

 

Another modern valence definition stating the valence meaning is that the valence of a particular atom present in a molecule is the number of electrons that an atom uses in the formation of a bond. This is represented by the formulas for calculating the valence electrons that can also be used to define valence is:

 

Valence = number of electrons in the last/valence shell of a free atom – Number of electrons on an atom in molecules that are not bonded. Hence, valency definition in chemistry can be shown by the formula as

 

Valence or Valency = Number of bonds formed + Formal charge of the atom.

The Valency and Number of Electrons

The Rutherford Model of the nucleus of an atom shows that the outside of an atom is filled by electrons, suggesting that the electrons are the ones responsible for the interaction of the atoms and the formation of the chemical bonds. Later, G. N. Lewis explained the valence and chemical bonding in terms of the nature of atoms to acquire a stable octet of eight valence-shell electrons. According to the theory proposed by Lewis, covalent bond formation leads to octet structure by sharing of the electrons, while ionic bonding leads to octet structure by the transfer of electrons from one atom to the other. 

 

Another term related to valence is covalence, which is the number of electron pairs shared by one atom with another atom. Also, by name co- means together, indicating that a covalent bond is that bond in which the atoms share a valence. Hence, it is now more common to say covalent bonds rather than using valence and valence meaning in Chemistry in high-level work done in advancing the theory of chemical bonding although it is widely used in the understanding of the basic concepts which provide an introduction to the topic.

 

Linus Pauling, during the 1930s, proposed the existence of polar covalent bonds which are possible intermediaries in between the covalent and the ionic bond. He also stated that the degree of the ionic character in such a bond was influenced by the electronegativity of the two atoms participating in a bond formation. He also considered the hypervalent molecules. These molecules are the ones in which the main group of elements have valences greater than the maximum of 4 allowed valences by the octet rule. 

 

An example of this case is the sulphur hexafluoride molecule (SF6), where according to Pauling the sulfur forms six two-electron bonds using sp3d2 hybridization of the atomic orbitals, merging one s, three p and two d orbitals. But the recent quantum mechanical calculations on this and similar types of molecules show that the role of the d-orbitals in such bonding is minimal and the SF6 molecule has to be described as having six polar covalent bonds, which are also partly ionic, made from only four of the orbitals on sulfur which is one s and three p following the octet rule, along with six orbitals on the fluorines. Similar calculations on transition-metal molecules also show that the role of p orbitals is min
or, and hence one s and five d orbitals on the metal are sufficient enough to describe the bonding.

Here are Some Examples of Valencies:

The valencies of some common elements are as follows:

Valency is Applied in Various Areas:

1) In Medicine: valency is used to determine the efficacy of a drug. Valency predicts how much drug will be needed in order to treat a patient. Valency also determines how easily a drug can cross biological membranes such as the placenta (for pregnant women), blood-brain barrier (for patients with neurodegenerative diseases like Alzheimer’s or Parkinson’s), and intestinal wall (for patients who need treatment for infections).

2) In Genetics: valency results from the binding of two alleles at a single loci, where each allele may have a different valence depending on its own gene product and that of another allele present at the same locus.

3) In Environmental Sciences: valency indicates the degree to which chemicals will interact with each other and the potential for chemical reaction.

4) In Industrial Chemistry: valency is used to predict the properties of compounds and their suitability for particular applications.

5) In Predicting the Properties of the Compound- valency helps in predicting the physical and chemical properties of the valency.

6) In Synthetic Organic Chemistry: valency is used to plan the construction of molecular structures.

7) In Studying the Structure of Inorganic Materials: valency provides a simple way of classifying complex inorganic materials.

8) In Studying the Bonding in Metals: valency is used to understand why some alloys have better mechanical properties than others.

9) In Solid-State Physics: valency is used to classify solids on the basis of their bonding arrangements.

10) Valency has wide applicability across many scientific disciplines. By understanding valency, we can better predict how chemicals will react with each other and create new compounds for various applications. Valency is a fundamental concept in chemistry.

Here are Some Tips to Study Valency:

1) Know the Basics- It is important to know the valencies of the common elements. This will give you a basic understanding of valency.

2) Practice Identifying Valencies- Try to identify the valency of different elements. This will help you better understand how valency works.

3) Use Valency to Predict Chemical Reactions- By understanding valency, you can better predict how chemicals will react with each other. This can help you create new compounds for various applications.

4) Review Key Concepts Regularly- valency is a complex concept, and it is important to review key concepts regularly. This will help you better understand valency and its applications.

5) Ask Questions- If you don’t understand something, ask your teacher or classmates for help. Nobody knows everything and collaboration can be very effective in valency.

6) Avoid Cramming- while studying valency one should avoid cramming. This will only lead to confusion and frustration. Valency should be studied gradually, and one should allow enough time to fully understand the concept.