Different atomic model

Atomic model

To explain the characteristics of atom and structure of atom there have few important model of atom that can give some clear idea about atom. Among these atomic models the most popular and well known atomic model is Rutherford's atomic model and Bohr's atomic model. Though there have some limitations these atomic models opens a new door in chemistry and physics.

Law of conservation

Newtons first law pf motion derived that force on any substance is zero the substance will propagate in same velocity by a straight line. Hence velocity is constant with time. Therefore the momentum will be constant with time. That follows the law of conservation of momentum. But from the definition of momentum we know that momentum is the multiplication of mass and velocity. With the increasing of mass the momentum will be increases. Again with the increasing of velocity the momentum will be increases. The law of conservation of momentum may states as "when the net force on any system is equal to zero then the sum of total momentum will follow the conservative nature".

Laws of motion

In 1687 Sir Isaac Newton established a relationship among mass, motion and force in his famous book named "Naturalasis Philosophia Principia" which is very important in theoretical physics. This law is called Newton's law of motion. These laws are Newton's First Law of motion, Newton's second law of motion and Newton's third law of motion. Theses three laws of motion can explain more complex topics of theoretical physics. Newton's first law of motion explains that without any external force a stationary substance will remain in rest and a moving substance will remain moving. Newton's first law of motion is also called the theory of inertia. In theoretical physics inertia is defined as the restriction against any change. There have a lot of variables in theoretical physics which values and measures are found from the Newtons law of motion. In absence of any external force the acceleration of moving substance will be zero. According to the Newtons second law of motion the rate of the momentum changing is proportional to the force. The direction of the force is as same as the direction of the momentum. Momentum is the multiplication of the mass and velocity.

First law

If external force does not implement then any stationary object will remain stable and any moving object will remain moving. Just think you a train is moving. Theen the engine o the train switched off then it tempts to stable. In this case the attempt of stabilising the movement of the object is gravitation and friction. If gravitation and friction do shall not act on the object, the object will remain moving.

Second law of motion

According to second law of motion, in any time the rate of change of the momentum of any object is proportional to the exerted force on the object. The second law of motion is specially focuses on the momentum of the object. Momentum is the measure of any object that is equal to the mass multiplied by the velocity of the object.

Let us consider a good example of second law of motion. If velocity of two objects ofotion is same and it hit on another object, how force the second object will feel is dependent on the mass of the objects. In this case more massive object will create more force. And less massive object will create less force.

From the second law of motion another very important equation can derive. That is force is equal to the mass multiplied by the acceleration.

F = ma

Where F is denoted for force, m is denoted for mass of the objects and a is demoted for the acceleration of the objects.

Third law of motion

Third law of motion says that every action have its equal and opposite reaction. Just think you putted a fruit on a table. The table is making force on the fruit. As same as the fruit is also making force on the table. Two forces are acting upon each other belongs to opposite direction.

Another, very common example may given. You jumped to land from boat. Very wonder you Will feel that you became forwarder and the boat became backward. This phenomenon happened for the cause that you made a force on the boat and as same the boat also made force on you. The two of the exerted force are equal and opposite direction.

Let any substance putting on a surface. What is happening between these two objects. Both two of the objects are exerting force on each another in opposite direction

Limitation of motion law

Motion law is not limitation free. With the emergence of modern physics Newton's motion law facing some of the limitations. Though, it never be ignore that once the maximum theory of the physics was established on the basis of motion law of Newton. Basically Newton's motion law is the basis of classical mechanics. But in the modern era of physics classical mechanics is out dated in terms of explaining microscopic particles motion. Hence, motion law is only applicable in explaining the behaviour of massive objects motion. It can never explain the speed of light and electron like particles.

In the third law of motion there explained that if external force does not exerts then stationary body will remain stable and moving body will remain moving. But in modern physics considering the cosmological view, the conception of stable bodies are ignored by few scientists. Because, in our universe everything is considered as the moving objects.

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VSEPR theorem

The expanded form of VSEPR is Valence Shell Electron Pair Repulsion. In 1970 scientist R.G Gillespie proposed Valence Shell Electron Pair Repulsion theorem that is simply expressed as VSEPR theorem. VSEPR theorem is established on the basis of Lewis structure of molecules. According to the Lewis structure of molecule, the central atoms valence shell contains electrons as pairs and more electron pairs may exists in valence shell. In a molecule the electron pairs tends to place them as far as possible from each others to minimise the repulsion between the pairs of electrons. Hence, different molecules are found in different shapes. Just for example the carbon di oxide is linear in structure. On the other hand the structure of water is just like English alphabet V. The every structure of molecules are the result of the electron pair repulsion of valence shell of the central atom. From different arrangement of the electron pair of valence shell of the central atom of the molecule, the angle of paired electron, atom and paired electron bond angle 180 degree ensures minimum repulsion between the electron pairs. 180 degree angle also ensures the maximum distance of the electron pairs. 180 degree of angle also ensures the shapes of molecule as linear and straight line structure.

Molecular orbital theorem

Valence Bond Theorem explains the formation of covalent bond within compound molecule. To form a covalent bond there may have different way of overlapping the electron clouds. What is the better way of forming covalent bond?  Molecular orbital theorem explains the better way of covalent bond formation. According to molecular orbital theory of formation of covalent bond, all of the atomic orbital forms a molecular orbital by combining and mixing. This new orbital structure is different from the atomic orbital structure. To form new molecular orbital all of the atomic orbitals distributed in a systematic pattern. The number of new formed molecular orbital is equal to the number of atomic orbital. The molecular orbital theorem constitutes with some basic features. Molecules are different from the its constituent atoms.
 Molecular orbital forms by combining of the atomic orbital of the atoms. The shapes of the molecular orbital is related on the shape of atomic orbitals. Molecular orbitals process definite energy levels. In molecular orbital theorem electrons are considered as the moving nature with the impacts of nuclei.

Valence Bond Theory

Valence bond theory explains the formation of covalent bond.  According to Heitler and London the covalent Bond forms by overlapping of electron cloud of the atoms. Only the condition of forming covalent bond between two atoms is the overlapping of electron clouds of two atom with each others. Methane is a compound with carbon and hydrogen. The bond between carbon and hydrogen is covalent bond. This bonds forms by overlapping of electron cloud of carbon with the electron cloud of hydrogen. How strong will be the covalent bond? It depends on the nature of overlapping. Maximum overlapping of electron cloud ensures maximum strength of bond. The principle discussion of valence bond theory is the overlapping of electron clouds. Overlapping also follows some conditions. These are as follows. The orbital that will participate in overlapping to form bond must have only one electron. Orbital containing a pair of electron can not do this. To make an effective overlapping atoms with valence electron must have to sufficiently closer to each other. Though Valence Bond Theory explains the causes of covalent bond, but yet it have some limitation. The limitation of valence bond theory is explained here.Presence of other nuclei changed the electronic arrangement of molecules.  Valence bond theory can not explain the paramagnetic character of oxygen. In the study of chemistry there may found some electron deficient compound in nature. Valence Bond Theory can not explains the bonding of these compounds. Valence Bond Theory can not explains the all properties of the compounds with resonating structure.

Internal energy of a system

If we consider a thermodynamic system, it must contain some matter and energy. There may have different energy concerning. These energy is the sum of kinetic energy of the molecules, rotational energy, vibrational energies and other concerned energy. Exactly to say internal energy of a system is the total energy of the system. Internal energy of a system can be expressed as the state function. The reason of calling internal energy as the state function is that it is determined by the state of a system. But it is independent of the paths of obtaining. For example, temperature, volume and pressure these are internal energy. These energy is determined by the state of the system, but not with the path. Let you are heating 0 degree Celsius of water. Once the temperature of water reaches to 1000 degree Celsius. The changed energy is calculated. It is 1.8 Kcal. In every experiment you will find same result. If you do experiment by electrically or physically heating or in any other way.

System

System is the spheres where chemical and physical process happens and this part is under thermodynamic study that is separated from the surroundings. The example of a system is oxygen in a cylinder. The outside of the cylinder is the surroundings. On the basis of phase, system are homogeneous and heterogeneous. The system consists of one phase is called homogeneous. The system consist with more phase is called heterogeneous system. The examples of thermodynamic homogeneous system is single solid, gas, true solution, mixture of gasses. Examples of heterogeneous system is ice on water. On the basis of the boundary, thermodynamic system are in three class. These are isolated system, closed system and open system. Isolated can not transfer matter and energy both. Closed system cannot transfer matter but can transfer energy in form of heat. The open system can transfers both heat and matter.

Lattice energy

When an atom donates electron it forms positive ion. When any atom gains electron it forms negative ion. In order to form a new compound these oppositely charged ion must have to combine together. When positively charged ion and negatively charged ion combine together and forms new compound some energy releases. The released energy to form one mole of compound by combining the anion and cation is termed as lattice energy. Lattice energy determines the nature of the bond. How strength the bond will be that depends on lattice energy. Greater the lattice energy greater the ionic bonds strength. The strength of the ionic bond and lattice energy relationship can express graphically. If we plot lattice energy vs strength of the ionic bond, there found that increasing of ionic bond with increasing of lattice energy. Some factors can influence on lattice energy. These factors are size of the ion and charges on ion.

Valence electron

To define valence electron of an atom first let us give definition of valence. Valence of an atom in a molecule is the number of bond concerned with this atom in molecule. Just for example, in methane carbon atom is bonded with 4 hydrogens. Each hydrogen is connected with carbon by single bond. Four hydrogen atom bonded with one carbon by 4 single bond. Hence, the number of bond concerned with carbon is 4. Hence, the valence of carbon atom in methane molecule is four. The valence electron is the number of electron available in outer shell of atom that can participate in the forming of bond. In an atom there may have a large number of electron surrounding the nucleus.But all of the electrons do not participate in bond formation and are not available ifor bond formation. In methane though carbon have number six electrons, only 4 electrons involved in formation of bond. These electrons available for bond forming in outer shell of atom is called valence electron. In carbon the valance electron is four. In a molecule each valence electron of an atom may not involved in bond forming. For example, the outer shell of hydrogen atom contains only one electron and the outer shell of chlorine contains 7 electrons. Hence, the valence electron of hydrogen is 1 and chlorine is 7. But in HCl molecule number one valence electron of chlorine atom is involved in bond formation. The valence electron that forms bond is called bonding electron. The rest of the electrons that do not take place in bond formation, but available for bond formation is called non bonding electron.

Isotopes

Two or more atoms these neutron number is not same but proton number is same are isotopes of each other. Another definition of isotopes are atoms with same atomic number but different mass number. Mass number of an atom is the sum of proton number and neutron number. Proton number is the atomic number of an atom. If proton number is same in two different atom it is possible to find different mass number if the neutron number is different. If two or more atoms are found with same proton number but different mass number they are isotopes of each others. The most common example of isotope is carbon-12 and carbon-14. In both atom the proton number is 6 but mass number is different. Hence the neutron number is also different. Hence, carbon-12 and carbon-14 is isotope of each other. In carbon-12 isotope the neutron number is six but in carbon-14 isotope the neutron number is eight.The another important isotopes of hydrogen atom is hydrogen, deuterium and tritium. Oxygen also have isotopes. The isotopes of oxygen are found where the the mass number is respectively 16, 17 and 18. Chlorine-35 and chlorine-37 are the two isotopes of chlorine where the atomic number or proton number is same but mass number or neutron number is different.

Electronegativity

From the word electronegativity it can imagine or guess about the meanings of electronegativity. Simply it means the capability of any atom to becoming negatively charged by attracting electron closer to it. In an covalent bond two or more atoms bonded with each other by sharing of electron. An electron cloud exists between two atoms. Each electron will not equally show an attraction with electron cloud. The atom that have higher attraction with electron, the electron cloud will get more closer to it. Hence, it will be partially negatively charged and rest will be partiality positively charged. Hence, Electronegativity can be defined as the attraction of an atom towards the electron in electron pair bond that enables electron cloud to become more dense surrounding this atom. For more density of the electron cloud near the high electronegative atom, it shows partially negatively charged.In chemistry there have a wide range of importance of electronegativity of atom. Electronegativity helps to predict the polarity, ionic character of covalent bond, inductive effects, determining the shapes of molecule.

Electron affinity

Definition of electron affinity

 

Electron affinity can be termed as the energy released to ad an electron with an atom.

 Explanation of Electron affinity

Electron affinity is the opposite term of ionisation energy. Where ionisation energy
 or ionisation potential means the requirement of energy to release electron from nutral atom or ion there electron affinity means the release of energy to ad an electron with atom or ion. Let a positive ion or a neutral atom are going to convert into a negatively charged ion by addition of an electron from outside. To do this there need some electron to release. This released electron is called electron affinity. Electron affinity may be classified into different class. First electron affinity and second electron affinity, etc. First electron affinity is the energy releasing for adding first electron with atom in gaseous state. On the other hand the released energy to adding the second electron with atom is called second electron affinity.

 Examples of electron affinity

Chlorine is an element of halogen group and chlorine is considered as nutral atom with zero charge to which an electron will add.

An electron added with neutral chlorine and chlorine converted into chloride ion. In course of converting some energy will release. This energy is termed as electron affinity.

Ionization energy

Ionization energy is the energy needed to remove electron from an atom in gaseous state. An atom is neutral in charge. If an atom required to transform into positive ion there need one or more electron remove. We know each of the electron orbits surrounding the nucleus with maintaining an attraction force between nucleus and atom. To remove an electron from an atomic shell there needs to overcome the attraction force between nucleus and electron.  This energy is termed as ionization energy. Unit of ionization energy is eV per atom or kilojoules per mole. One eV is equal to 96.84 kilojoul per mole. Ionization energy is also called ionization potential. Ionization energy may classified into different class. Such as first ionization energy and second ionization energy. First ionization is the required energy in order to remove first electron from the atom. After removing one electron from atom, if there required another electron to remove from atom there need additional amount of energy to remove the second electron. This required energy is called second ionization energy. For sufficient of ionization energy the electron removes from the neutral atom and finally atom is convert into ion.

Colloids and classification of colloids

Colloid is the states and conditions of a mixture when the dispersed substance in the solvent media lies between 10 Amstrong to 2000 Amstrong in diameter. The particles or substance of such sizes is also called colloidal state. On the basis of the size of the dispersed media colloid is to define as the middle state between true solution and suspension. In a true solution the diameter of the dispersed substance is between 1 Amstrong to 10 Amstrong. But in suspension the diameter of the dispersed substance is more than 2000 Amstrong. First Thomas Graham studied the behaviour of diffusable substance. He found that some substance are diffusible in the solvent through permeable membrane and other are not. He called first as crystalloid and others are colloid. On the basis of dispersed particle and dispersion media there found eight types of colloid.  The particles that distributed in a colloidal solution is called dispersed phase and where the particles are dispersed is called disperaion media. If the dispersed phase is solid and the dispersion media is liquid then it is called sol. If the dispersed phase dispersed into water then the colloid is Call d Hydrosol. If liquid is dispersed into liquuid then colloid is called emulsion. The liquid if dispersed onto gas, the colloid is called aerosol.

Heisenberg's uncertainty principle

Heisenberg's uncertainty principle is the the principle that describes he dual nature of matter. The conjugate properties of matter if we try to measure, there will an uncertainty happen to measuring both properties simultaneously. Conjugate properties are these properties these are independent. For an electron the conjugate properries are position and momentum. According to principle of uncertainty the two conjugate properties cannot measure simaltaneously. Hence, according to uncertainty it is imposible to measure position and momentum of the electron simultaneously. If one of the property can measures certainly then other property will become uncertain in measurement and determinition. Let, position of the electron can accurately measure then the momentum will be uncertain. The product of the uncertainty of position and the uncertainty of the momentum is equal and greater than the value planks constant, h devided by the double of 3.14. The Heisenberg uncertainty equation shows that the increasing the uncertainty of measuring position decreases the uncertainty of measuring momentum. As same as if the uncertainty of measuring momentum is very high then the uncertainty of measuring position will be very small. For larger matter the uncertainty will be negligible. The uncertainty of an  electron may be noticeable, but the uncertainty of a one kg stone is negligible. This for the cause of mass. Momentum is the product of mass and velocity. If mass is very big the uncertainty will be verry small and negligible. Why it is impossible to measure momentum and position of electron is quite impossible simaltaneously? Just consider you are trying to measure the position of an electron. A supermicroscope is taken to do this. Only the condition of seeing any object is photon must fall into it and a light must have to reflect from the surface of this object. In electron when in any moment if photon strike electron, at that moment electron changes its momentum

With the emergence of particle physics, besides of electron, proton, neutron another elementary particles have been discovered. There have 12 elementary particles in our universe including last discovered elementary particle higgs boson by CERN scientist that was previously predicted by standard model of particle physics.  These elementary particles such as electron, proton, neutron, lepton and quarks shows the uncertainty.

According to Heisenberg uncertainty principle it is quite impossible to determine the position and momentum simultaneously.

The mathematical relationship of Heisenberg's uncertainty principle is as below,

Uncertainty involved in the position × Uncertainty involved in momentum > h÷2π

Or

Uncertainty of podition × Uncertainty of Momentum = h÷2π

In above relationship h is planks constant

From the above relationship it is found that uncertainty of position and uncertainty of momentum is inversely proportional to each other. That means is one uncertainty be very large then uncertainty of others will be very low.

Just condider a particle just like electron that moves approximately with a speed of light. Inthat case this should be possible of gaining ount of momentum in normal scence. In that case the uncertainty of the position of the electron will be very high.

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Rutherford's atomic model

In 1909 Rutherford and Marsden did an experiment that is called Alpha particles scattering experiment. This experiment proves some of the characteristics of nucleus and electron. Based on the Alpha particle scattering experiment Rutherford proposed a model of atom. This is Rutherfords atomic model. According to Rutherford's atomic model, Nucleus is the dense and central particles of an atom that is positively charged and contails the all of mass of atom. The volume of nucleus is negligible with comparing with the volume of the atom. The electron is negatively charged particles that move surrounding the nucleus just like the movement of plannet surrounding the sun. In alpha particle scattering experiment we see that the alpha paticle that is near by the nucleus that is more deflected. Some particles will never cross the atom and reflected from nucleus. We know that alpha particle is positively charged. This deflection of alpha particles happens due to the repulsion of the positively charged nucleus.

Wave nature of electron

Electron have two nature. One is wave nature and another is particle nature. Scientist D Broglie sugested the wave nature of electron. The experiment of Davison and Garmer also prove the wave nature of electron. X-ray is a wave. The electron behaves like X-ray when the beam of electron is passed through crystal. When X-ray is passed through a crystal then X-ray is diffract. As same as a beam of electron if passed through the crystal, electron beam shows diffraction. This behavior of electron to diffraction shows the wave nature of the electron. The discovery of wave nature of electron have made a wide range of scientific research and helped to establish different theories and postulations. Thomson also propose a posibility of producing secondary X-ray The electron that passage through crystal is able to produce secondary crystal. Schrödinger wave equation is established on the base of the conception about electron that electron pocesses wave nature.  The movement of electron around the nucleus is in wave nature.

Wave particle duality conception shows that particle shows two nature. One is particle behaviour and another is wave behaviour. Electron is the most well knoen example of wave particle duality conception.

The evidence of wave particle duality found from different theories of modern pjysics and chemistry.

Now let us consider about a discussion about wave and particle. Once a day the atom was considered as the unique smaller building block of the entire matter of the universe. But with the development of modern physics these conception of atom as a smaller building block of the universe have been became outdated. Number twelve elementary particles have been discovered. These elementary particles are comsidered as the smaller comstituent of atom. At last discovered elementary particle by CERN scientist is called Higgs Boson particle thst was predicted by the standard model of particle physics. Higgs Boson particles are considered as the key particles that ptovide mass to other particles.

Wave is an unique important part of physics. Most of the physics physical phenomenon pocess a property that is called wave. The term wave is concerned with the rhythmical movement of something. Wave shows oscillating properties.