Bohr’s Atomic Model

Neil Bohr in 1913 AD formulated an atomic model based on Planck’s quantum theory of radiation and some classical concept of physics. The atomic model has following postulates or assumption:

Ø  Electron revolves around the nucleus in a selected circular orbital path called orbit.

Ø  Electron doesn’t lose or gain energy when revolves around the nucleus such a state of electron is called stationary state. Stationary energy of electron is constant but its motion change with time. This postulate justify about stability of atom.

Ø  The centrifugal force of electron is balanced by electrostatic force of attraction between nucleus and electron i.e.

          where  m = mass of electron

            r = radius of orbit

              Z = atomic number

              v = velocity of electron

              E₀ = permitivity of medim

Ø  Electron can revolve only in those orbits in which angular momentum of revolvingelectron is an integral multiple of h/2π i.e.

                 where, h = Planck’s constant = 6.62 x 10^-34 JS
                               n = an integer called principle quantum number = 1, 2, 3, ………

Ø  The absorption or emission of energy can occur on by transition of electron from lower to higher energy level or vice-versa. Energy is absorbed when an electron jump from lower state to higher state and energy is emit when an electron jump from higher to lower energy state. The difference of energy is ΔE and is equal to one quanta of energy i.e.

                                                        E_higer – E_lower = ΔE = hf

.

Drawback of Bohr’s Model

ü  Bohr’s model fail to explain spectrum of multi-electron system

ü  It doesn’t explain the splitting of spectral lines under electric field (Stark effect) and magnetic field (Zeeman effect)

ü  It fails to explain line spectrum of hydrogen

ü  This theory is not accordance with Heisenberg’s uncertainty principle

 

Rutherford’s Atomic Model

 

Ø    Rutherford (1911) did an experiment in which bombardment of thin gold coated with  ZnS with high speed positively charged α – particles emitted from radioactive substance. This experiment leads to discovery of nucleus. 

   In this experiment, a piece of radioactive substance (Radium) is placed in a lead block.Radium emitting a beam of alpha particle in all directions. The block is constructed in such a way with slits that only a narrow beam of α – particle could escape. Thin stream of α – particles comes out of holes and remaining absorbed by lead plate. This beam of α – particle then passes through thin gold foil. In order to detect α – particle after scattering, a movable circular screen coated with Zinc Sulphide is placed around the gold foil. When α – particles hit the screen, they produce flash of light which could be counted. 

                                             Figure: Rutherford’s α-rays scattering experiment

Ø Result of this experiment 

·        Most of α – particle (99%) passed through foil without undergoing any deflection

·        Few α – particles underwent deflection through small angel

·        Very very few (only one of 10000) were deflected back

Explanation

 

To deflect an α – particle right back to its path, somethings of its own mass and charge is needed. The electron are too small as compared tp α – particle ( an α – particle is 7000 times heavier than an electron) to deflect α – particle out of their course.

·        Since some α – particle were deflected back and α – particles are heavy paericle, these would be deflected back only when they strike some heavier body(nucleus) inside the atom most of α – particle passed through the foil means that remaining part of atom is hollow. So, Rutherford conclude that nucleus of atom contains most of atomic mass.

·        Since few α – particle were deflected through small angle and α – particle were positively charged particle, these could be deflected only by some positively body present within the atom (nucleus) i.e. nucleus of atom is positively charged.

·        Since most of α – particle passed through the foil without undergoing any deflection, there must be sufficient empty space within the atom i.e. atom consist of mostly empty space.

Postulates:

·        Atom has a tiny dense central core or nucleus which contains the entire mass of atom.

·        Atom consists of mostly empty space.

·        The size nucleus is extremely small as compared to size of atom.

·        Nucleus of atom is positively charged.

·        As the atom on the whole is neutral, there is one electron for each positive charge on nucleus.

·        The atom consists of central nucleus surrounded by electron which is revolving around the nucleus like planet revolving round the sun.

·        Electron and nucleus are held together by coulombic force of attraction.
Note:
Radius of atom is 10^-8cm which is 100000 time greater than the radius of nucleus (radius of nucleus = 10^-13cm)

Drawback of Rutherford’s Atomic Model

·        When an electron revolves around the nucleus, it will radiate out energy, resulting in the loss of energy. This loss of energy will make the electron to move slowly and consequently it will be moving in a spiral path and ultimately falls on the nucleus. Thus, such an atomic model and atom are unstable. Fortunately, the atom is stable.

·        Atomic spectra of the elements should be continuous band spectra but atoms are characterized by line spectra (discontinuous)

Types of Atomic Species

 

1. Isotopes: (Iso = same, topos = place)

Ø  Atom of the same element having same atomic number but different mass number.

Ø  They have same chemical properties and different physical properties

Ø  They contain equal number of electron and same electron configuration for e.g. a.₁H¹, ₁H², ₁H³, b. ₁₇C¹³⁵, ₁₇c¹³⁷

Ø  Physical properties likes density, rate of diffusion etc. of isotopes are different because they depend upon the mass number

2. Isobars

Ø  Atoms of different element having same mass number but different atomic number

Ø  They have different chemical properties for e.g.
a. ₆c¹⁴, ₇N¹⁴
b. ₁₈Ar⁴⁰₁₉K⁴⁰, ₂₀Ca⁴⁰, etc.

3. Isotones

Ø  Atoms of different elements having the same number of neutrons e.g.
a. ₆C¹³, ₇N¹⁴
b. ₁H³, ₂He⁴, etc

4. Isosters

Ø  Species having same number of atoms and electron e.g.
a. HCl & F₂
b. N₂& CO
c. N₂O₄CO₂­, etc.

5. Isodiapheres

Ø  These are the atoms of same difference in number of protons and neutrons e.g.
a. ₉₂U²³⁵, ₉₀Th²³¹
b. ₂₉Cu⁶⁵, ₂₄Cr⁵⁴ etc.

6. Isomorphs

Ø  Identical crystal structure, similar constituent and chemical formulae for e.g. K₂SO₄, K₂CrO₄, (valance of S, Cr is 6)

7. Isoelectronic

Ø  Atoms or compounds having same no. of electron and electronic configuration for e.g.
a. N₂O, CO₂
b. H^-, He, Li⁺
c. N₂O, CO₂, etc.

Polymer

Polymer is the big molecules having high molecular mass which are obtained by the combination of large number of small molecule called monomer. The term ‘polymer’ derived from Greek word and has meaning many parts. Polymers are materials made of long, repeating chains of molecules.

A polymer can be a three dimensional organization (think about the rehashing units connected together left and right, front and back, here and there) or two-dimensional organization (think about the rehashing units connected together left, right, up, and down in a sheet) or a one-dimensional organization (think about the rehashing units connected left and right in a chain). Each rehashing unit is the "- mer" or essential unit with "poly-mer" which means many rehashing units. Rehashing units are frequently made of carbon and hydrogen and in some cases oxygen, nitrogen, sulfur, chlorine, fluorine, phosphorous, and silicon. To make the chain, numerous connections or "- mers" are artificially snared or polymerized together. Connecting innumerable portions of development paper together to make paper laurels or snaring together several paper clasps to shape chains, or hanging dabs envisions polymers.

Polymers are both man-made and normally happening. Elastic, for instance, is a characteristic polymeric material that has been utilized for a great many years. It has superb flexible characteristics, the consequence of a sub-atomic polymer chain made by earth. Another characteristic polymer is shellac, a gum created by the lac bug in India and Thailand, which is utilized as a paint preliminary, sealant, and stain. From the strand of our DNA which is a normally happening biopolymer to polypropylene which is utilized all through the world as plastic.

Polymers are not limited to monomers of a similar substance arrangement or sub-atomic weight and structure. Some characteristic polymers are made out of one sort of monomer. Generally characteristic and engineered polymers, be that as it may, are comprised of at least two unique kinds of monomers; such polymers are known as copolymers.

Polymers might be normally found in plants and creatures (characteristic polymers) or might be man-made (manufactured polymers). Various polymers have various one of a kind physical and substance properties because of which they discover use in regular daily existence. Contingent upon the ideal use, polymers can be calibrated to use certain worthwhile properties. These include:

• Reflectivity: Some polymers are used to produce reflective film, which is used in a variety of light-related technologies.
• Impact Resistance: Sturdy plastics that can withstand rough handling are perfect for luggage, protective cases, car bumpers, and more.
• Brittleness: Some forms of polystyrene are hard and brittle and easy to deform using heat.
• Translucence: See-through polymers, including polymer clay, are often used in arts and crafts.
• Ductility: Unlike brittle polymers, ductile polymers can be deformed without falling apart. Metals such as gold, aluminum, and steel are known for their ductility. Ductile polymers, while not as strong as other polymers, are useful for many purposes.
• Elasticity: Natural and synthetic rubbers have elastic properties that make them ideal for car tires and similar products.

Organic polymers play a crucial role in living things, providing basic structural materials and participating in vital life processes. For example, the solid parts of all plants are made up of polymers. These include cellulose, lignin, and various resins. Cellulose is a polysaccharide, a polymer that is composed of sugar molecules. Lignin consists of a complicated three-dimensional network of polymers. Wood resins are polymers of a simple hydrocarbon, isoprene. Another familiar isoprene polymer is rubber.

Other important natural polymers include the proteins, which are polymers of amino acids, and the nucleic acids, which are polymers of nucleotides—complex molecules composed of nitrogen-containing bases, sugars, and phosphoric acid. The nucleic acids carry genetic information in the cell. Starches, important sources of food energy derived from plants, are natural polymers composed of glucose.

Many inorganic polymers also are found in nature, including diamond and graphite. Both are composed of carbon. In diamond, carbon atoms are linked in a three-dimensional network that gives the material its hardness. In graphite, used as a lubricant and in pencil “leads,” the carbon atoms link in planes that can slide across one another.

Synthetic polymers are produced in different types of reactions. Many simple hydrocarbons, such as ethylene and propylene, can be transformed into polymers by adding one monomer after another to the growing chain. Polyethylene, composed of repeating ethylene monomers, is an addition polymer. It may have as many as 10,000 monomers joined in long coiled chains. Polyethylene is crystalline, translucent, and thermoplastic—i.e., it softens when heated. It is used for coatings, packaging, molded parts, and the manufacture of bottles and containers. Polypropylene is also crystalline and thermoplastic but is harder than polyethylene. Its molecules may consist of from 50,000 to 200,000 monomers. This compound is used in the textile industry and to make molded objects.

Other addition polymers include polybutadiene, polyisoprene, and polychloroprene, which are all important in the manufacture of synthetic rubbers. Some polymers, such as polystyrene, are glassy and transparent at room temperature, as well as being thermoplastic. Polystyrene can be coloured any shade and is used in the manufacture of toys and other plastic objects.

If one hydrogen atom in ethylene is replaced by a chlorine atom, vinyl chloride is produced. This polymerizes to polyvinyl chloride (PVC), a colourless, hard, tough, thermoplastic material that can be manufactured in a number of forms, including foams, films, and fibres. Vinyl acetate, produced by the reaction of ethylene and acetic acid, polymerizes to amorphous, soft resins used as coatings and adhesives. It copolymerizes with vinyl chloride to produce a large family of thermoplastic materials.

COVID-19

Corona virus disease (COVID-19) is an infectious disease caused by a newly discovered corona virus. Corona viruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the common cold (which is also caused by other viruses, predominantly rhinoviruses), while more lethal varieties can cause SARS, MERS, and COVID-19. In cows and pigs they cause diarrhea, while in mice they cause hepatitis and encephalomyelitis. There are as yet no vaccines or antiviral drugs to prevent or treat human corona virus infections.

Most people infected with the COVID-19 virus will experience mild to moderate respiratory illness and recover without requiring special treatment.  Older people and those with underlying medical problems like cardiovascular disease, diabetes, chronic respiratory disease, and cancer are more likely to develop serious illness.

The best way to prevent and slow down transmission is to be well informed about the COVID-19 virus, the disease it causes and how it spreads. Protect yourself and others from infection by washing your hands or using an alcohol based rub frequently and not touching your face. 

The COVID-19 virus spreads primarily through droplets of saliva or discharge from the nose when an infected person coughs or sneezes, so it’s important that you also practice respiratory etiquette (for example, by coughing into a flexed elbow).

COVID-19 affects different people in different ways. Most infected people will develop mild to moderate illness and recover without hospitalization.

 

·         Most common symptoms:

·         fever

·         dry cough

·         tiredness

·         Less common symptoms:

·         aches and pains

·         sore throat

·         diarrhoea

·         conjunctivitis

·         headache

·         loss of taste or smell

·         a rash on skin, or discolouration of fingers or toes

·         Serious symptoms:

·         difficulty breathing or shortness of breath

·         chest pain or pressure

·         loss of speech or movement

Seek immediate medical attention if you have serious symptoms. Always call before visiting your doctor or health facility.

People with mild symptoms who are otherwise healthy should manage their symptoms at home.

On average it takes 5–6 days from when someone is infected with the virus for symptoms to show, however it can take up to 14 days. To date, there are no specific vaccines or medicines for COVID-19. Treatments are under investigation, and will be tested through clinical trials. 

If you feel sick you should rest, drink plenty of fluid, and eat nutritious food. Stay in a separate room from other family members, and use a dedicated bathroom if possible. Clean and disinfect frequently touched surfaces.

Everyone should keep a healthy lifestyle at home. Maintain a healthy diet, sleep, stay active, and make social contact with loved ones through the phone or internet. Children need extra love and attention from adults during difficult times. Keep to regular routines and schedules as much as possible.

It is normal to feel sad, stressed, or confused during a crisis. Talking to people you trust, such as friends and family can help. If you feel overwhelmed, talk to a health worker or counselor.

Since 31 December 2019 and as of 17 November 2020, 55 154 651 cases of COVID-19 (in accordance with the applied case definitions and testing strategies in the affected countries) have been reported, including 1 328 537 deaths.

Since 31 December 2019 and as of 17 November 2020, 211, 475 cases of COVID-19 have been reported, including 1275 deaths.

 

 

chelate

CHELATES

       The ligands containing two or more bonding sites are the polydentate ligands. Any class of co-ordinate or complex compounds in which the polydentate ligands are attached through the two or more doner atoms to the same central ion forming the one or more rings or cyclic structure are called chelates.

       The polydentate ligands having two or more doner atom and are able to form many chelates are called as chelating agent or chelating ligands or chelating groups. Some chelating ligands are EN, EDTA, oxalate ion etc.

      The process by which the formation of such ring structure takes place with the chelating agent is called as chelation.

      The enhanced stability of complexes with chelated ligands( polydentate ) for a metal ion compared to the similar non-chelating ligands ( monodentate ) for the same metal during the complex formation is called as chelate effect. For example: [Ni(en)3]2+ is about 10  ^10 times stable than [Ni(NH3)6]2+.

      The increase in stability of chelate complexes is due to following reasons:

1.       Due to increase in the linkage sites.

2.       Due to formation of one or more rings.

3.       The entropy and enthalpy change for the chelate complexes are greater than non-chelated complexes.

                

                   chelate with one                          chelate with two                            chelate with three

            ethylenediamine ligands                    ethylenediamine ligands                    ethylenediamine ligand

In the two structures on the left, the bonding capacity of the Ni²⁺ ion is completed by water molecules. Each water molecule forms only one bond to Ni²⁺, so water is not a chelating agent. Because the chelating agent is attached to the metal ion by several bonds, chelates tend to be more stable than complexes formed with monodentate ligands such as water.

Porphine is a chelating agent similar to ethylenediamine in that it forms bonds to a metal ion through nitrogen atoms. Each of the four nitrogen atoms in the center of the molecule can form a bond to a metal ion. Porphine is the simplest of a group of chelating agents called porphyrins. Porphyrins have a structure derived from porphine by replacing some of the hydrogen atoms around the outside with other groups of atoms. 

       One important porphyrin chelate is heme, the central component of hemoglobin, which carries oxygen through the blood from the lungs to the tissues. Heme contains a porphyrin chelating agent bonded to an iron(II) ion. Iron, like nickel, can form six bonds. Four of these bonds tie it to the porphyrin. One of iron's two remaining bonds holds an oxygen molecule as it is transported through the blood. Chlorophyll is another porphyrin chelate. In chlorophyll, the metal at the center of the chelate is a magnesium ion. Chlorophyll, which is responsible for the green color of plant leaves, absorbs the light energy that is converted to chemical energy in the process of photosynthesis.

Another biologically significant chelate is vitamin B-12. It is the only vitamin that contains a metal, a cobalt(II) ion bonded to a porphyrin-like chelating agent. As far as is known, it is required in the diet of all higher animals. It is not synthesized by either higher plants or animals, but only by certain bacteria and molds. These are the sources of the B-12 found in animal products. Because vitamin B-12 is not found in higher plants, vegetarians must take care to include in their diets foods or supplements that contain the vitamin.

                                    

Hydroxyl apatite

                               

                                   Hydroxyl Apatite

Introduction

                     Hydroxyl apatite, also called hydroxy apatite (HA), is a naturally occuring minerals from calcium apatite with molecular formula [Ca5(PO4)3(OH)], but is usually written as [Ca10(PO4)6(OH)2]. Hydroxyl apatite is a main inorganic crystalline component in animal hard tissue such as bones and teeth. It content in natural animal teeth is 80-98% and in natural bones is over 60%. Upto 50% by volume  and 70% by weight of human bone is a modified from of hydroxyl apatite. It has been proved thet synthetic HA has good properties as bio-compatible, osteoconductive, non-toxic, non-imunogenic, bioceramic.

  Hydroxyl apatite can be synthetically prepared from natural source. Because bone defect arisen from cancer, injury and accident are most common in the clinic, a mass of HA are needed for restoration of bone defect.Therefore, both natural and synthetic kinds of HA are widely used as bioceramic in forms of particle, block and coating for the hard tissue repair. Synthetic HA can be prepared by means the wet and dry-method.

On the other hand, the production of HAp from natural sources is inexpensive and uncomplicated.The thermal calcination method is commonly used for the isolation of natural HAp. Tuna (Thunnusobesus) is a fish species of great commercial importance in the tropical and subtropical waters of the Pacific, Atlantic and Indian oceans. Specifically, Thunnus obesus occupies 12% of the total amount of fish production in Korea (Production Database of Ministry of Maritime Affairs and Fisheries of Korea). It is usually processed as canned food and sliced raw meat in a factory and the by-products of tuna are affluent and collected at once. The waste of Thunnus obesus has recently become a serious issue in coastal areas of Korea; one of the simplest ways to decrease pollution is the selective isolation of HAp from this waste. Ozawa et al., has reported the removal of aqueous chromium by fish bone waste originated HAp. Micro structural HAp has already been obtained from fish bone by thermal treatment , thermal decomposition, alkaline hydrothermal, sub critical water process from bovine bone, teeth and bones of pig, extracted human teeth and cuttle fish . Although much has been learned about HAp isolation from natural sources, the most important parameter, exact isolation temperature, remains poorly understood. In the present study, we have utilized Thunnus obesus bone as a new marine source for isolation of HAp and subjected the bone to various physiochemical properties, in order to find out the optimum conditions for HAp isolation. The derived HAp can be used for various medical and industrial applications and substantially increases the economical value of Thunnus obesus bone.

            

                            figure.  Needle-like hydroxyapatite crystals on stainless steel