Structure Of Atoms|Atomic Structure
Saturday 19 August 2017
Atom:-
An Atom is smallest indivisible constituent of matter.It means an atom cannot be divided into sub parts .Atom have sizes around 100 picometres.Every atom has a nucleus where all its mass get concentrated i.e almost 99.9% mass of an atom present in nucleus ,nucleus conation proton and neutron and electron revolves around nucleus which is binded by electro magnetic force between proton and electron an neutron have no charge.
Rutherford Experiment:
Rutherford gold foil experiment is a famous experiment in which he has fired alpha particles(helium nuclei) into a thin gold foil and observed below:-
Most of the particles pass through the foil without any deviation
Most pass with some deflection and some pass with heavy deflection like 90 degrees.
So he concluded that every atom consist of a central part in which all its mass is concentrated due to which such heavy deflection occured.
Thomson Model of an Atom:-
Thomson atomic model also know as plum pudding model raisin pudding watermelon model it was dicovered by Thomson in 1898.In this model thomson considered that an atom has spherical shape and in it postive charge is uniformly distributed and - ve charge embedded in such a manner to give electrostatic stability to the atom.The radius of atim is approzimateley 10-10
metre and mass is uniformly distributed in it.
Discharge Tube Experiment or cathode ray experiment:-
Cathode ray i.e electrons always travel from cathode towards anode and in the absense of any force which can be electric or magnetic field it travels in straight lines and in presence of these fields it shows behavious like negative particles which proves cathode rays are negativeley charged particles.
Their behaviour can be observed easily with the help of fluorescent or phosphorus sent material.In this experiment it is also bserved that cathode rays does not depend upon material of electrode and nature of gas present in dischrge tube so it is considered basic constituent particle electron which is negativeley charged.
Charge and mass of electron:-
R. A. Millikan has done oil drop experiment to determine charge of electron which came out to be -1.6× 10-19 C or -1.6022× 10-19 C
Mass of electron = 9.1094 ´ 10-31 kg
Electromagnetic Radiation:-
electromagnetic radiation refers to wave of electromagnetic field which is travelling in space and carrying electromagnetic radiant energy it includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-, and gamma radiation.
generally electromagnetic radiations are radiant energy which consist of continuous oscillation of electric and magnetic field ,they travel in the vacuum with the speed of light and their oscillation is perpendicular to each other and also perpendicular to the direction of wave propagation and energy
The position of electromagnetic waves at any time can be pointed in electromagnetic spectrum by its frequency or wavelength at any time.In general electromagnetic spectrum has increasing frequency and decreasing wavelength with distance.
Characterstics of wave:-
i. Wavelength : The distance between neighbouring
crests or troughs is known as wavelength. It is denoted by λ.
ii. Frequency: The number of times a wave passes through a given points per second is known as
frequency. It is denoted by v.
iii. Amplitude: It is the maximum height of crest or depth of trough of a wave. It is denoted by A.
iv. Velocity: The distance travelled by a wave in one second is called its velocity. All electromagnetic radiations travel with same velocity. It is denoted by c.
It is equal to3×10^8 m/sec.
v. Wave number : It is reciprocal of wavelength. It is denoted by v ̅=1/λ.
Wavelength and frequency:-
c=v λ.
C= Velocity of light,v= frequency and λ= wavelength
Planck's Quantum Theory:-
Photoelectric Effect:-
According to Planck when an photon hits a metallic surface a part of its energy called binding energy used for the the ejection of electron and rest is given to the ejected electron in the form of kinetic energy.
Showing it in equation:
E=Be+KE
Where, E= energy of incident photon
BE = binding energy
KE = kinetic energy of the ejected electron
Or hv = kinetic energy of the ejected electron
Bohr's Model:-
Heisenberg's Uncertainity Principle:-
It states that it is impossible to determine simultaneously, the exact position and exact momentum (or velocity) of an electron.The product of their uncertainties is always equal to or greater than h/4π.
Schrodinger's Equation:-
Schrodinger's Equation used in describing quantum mechanical behavior and it predicts analytically and precisely the probability of events or outcome.
Quantum Numbers :-
Their are four quantum numbers :-
1)Principal quantum number
2)Azimuthal quantum number
3)Magnetic quantum number
4)Electron spin
Quantum number specifies the size,shape and orientation of an orbital ,three quantum numbers needed to specify an orbital and to specify an electron all four quantum numbers needed.
Nodal surfaces or Nodes :-
The region where this probability density function reduces to zero is called nodal surfaces or simply nodes.
Sheilding effect or screening effect:-
The outer electron experiences less attraction of positive charge of nucleus due to inner electrons ,this effect is called screening effect it increase with increase in Azimuthal quantum numbers.
Aufbau Principle:-
In the ground state of atom the orbital are filled in order of their increaseing energies and the order is as follows:-
Below is the order in which orbitals are filled:-
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s..
Pauli Exclusion Principle :-
No two electron have the same set of four quantum numbers and only two electron may exist in the same orbital and they must have opposite spin
Hund's rule of maximum multiplicity :-
Pairing of electron will not take place in an orbital until the pairing subshell is singly occupied.
Electronic configuration of atoms:-
Arrangement of electrons in different orbitals of an atom.It is represente in two ways given below:-
Orbital diagram:, Each orbital of the subshell is represented by a box and the electron is represented by an arrow (↑) a positive spin or an arrow (↓) a negative spin and sapbdc...etc notation.
Stability of completely filled and half filled subshells :-
Symmetrical distribution of electrons- .completely filled or half filled sub-shells have symmetrical distribution of electrons in them and are more stable
Exchange energy-The two or more electrons with the same spin present in the degenerate orbitals of a sub-shell can exchange their position and the energy released due to this exchange is called exchange energy.The number of exchanges is maximum when the subshell is either half filled or completely filled. As a result the exchange energy is maximum and so is the stability.
An Atom is smallest indivisible constituent of matter.It means an atom cannot be divided into sub parts .Atom have sizes around 100 picometres.Every atom has a nucleus where all its mass get concentrated i.e almost 99.9% mass of an atom present in nucleus ,nucleus conation proton and neutron and electron revolves around nucleus which is binded by electro magnetic force between proton and electron an neutron have no charge.
In the nucleus proton and neutron is binded by nuclear force which is greater then the repulsive electro magnetic force between two proton in the nucleus.An atom mostly consist of same number of electron and proton .
If in any case an atom has fewer number of electron or more number of electron then protons then it is called an ion as it contains either positive or negative charge.
The number of proton represents to which chemical element certain atom belongs.so by knowing number of protons in an atom we can decide which element it is.
The neutron decides number of isotopes and the electron shows the magnetic properties of that atom
If in any case an atom has fewer number of electron or more number of electron then protons then it is called an ion as it contains either positive or negative charge.
The number of proton represents to which chemical element certain atom belongs.so by knowing number of protons in an atom we can decide which element it is.
The neutron decides number of isotopes and the electron shows the magnetic properties of that atom
Rutherford Experiment:
Rutherford gold foil experiment is a famous experiment in which he has fired alpha particles(helium nuclei) into a thin gold foil and observed below:-
Most of the particles pass through the foil without any deviation
Most pass with some deflection and some pass with heavy deflection like 90 degrees.
So he concluded that every atom consist of a central part in which all its mass is concentrated due to which such heavy deflection occured.
Thomson Model of an Atom:-
Thomson atomic model also know as plum pudding model raisin pudding watermelon model it was dicovered by Thomson in 1898.In this model thomson considered that an atom has spherical shape and in it postive charge is uniformly distributed and - ve charge embedded in such a manner to give electrostatic stability to the atom.The radius of atim is approzimateley 10-10
metre and mass is uniformly distributed in it.
Discharge Tube Experiment or cathode ray experiment:-
Cathode ray i.e electrons always travel from cathode towards anode and in the absense of any force which can be electric or magnetic field it travels in straight lines and in presence of these fields it shows behavious like negative particles which proves cathode rays are negativeley charged particles.
Their behaviour can be observed easily with the help of fluorescent or phosphorus sent material.In this experiment it is also bserved that cathode rays does not depend upon material of electrode and nature of gas present in dischrge tube so it is considered basic constituent particle electron which is negativeley charged.
Charge and mass of electron:-
R. A. Millikan has done oil drop experiment to determine charge of electron which came out to be -1.6× 10-19 C or -1.6022× 10-19 C
Mass of electron = 9.1094 ´ 10-31 kg
Electromagnetic Radiation:-
electromagnetic radiation refers to wave of electromagnetic field which is travelling in space and carrying electromagnetic radiant energy it includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-, and gamma radiation.
generally electromagnetic radiations are radiant energy which consist of continuous oscillation of electric and magnetic field ,they travel in the vacuum with the speed of light and their oscillation is perpendicular to each other and also perpendicular to the direction of wave propagation and energy
The position of electromagnetic waves at any time can be pointed in electromagnetic spectrum by its frequency or wavelength at any time.In general electromagnetic spectrum has increasing frequency and decreasing wavelength with distance.
Characterstics of wave:-
i. Wavelength : The distance between neighbouring
crests or troughs is known as wavelength. It is denoted by λ.
ii. Frequency: The number of times a wave passes through a given points per second is known as
frequency. It is denoted by v.
iii. Amplitude: It is the maximum height of crest or depth of trough of a wave. It is denoted by A.
iv. Velocity: The distance travelled by a wave in one second is called its velocity. All electromagnetic radiations travel with same velocity. It is denoted by c.
It is equal to
v. Wave number : It is reciprocal of wavelength. It is denoted by v ̅=1/λ.
Wavelength and frequency:-
c=v λ.
C= Velocity of light,v= frequency and λ= wavelength
Photoelectric Effect:-
According to Planck when an photon hits a metallic surface a part of its energy called binding energy used for the the ejection of electron and rest is given to the ejected electron in the form of kinetic energy.
Showing it in equation:
E=Be+KE
Where, E= energy of incident photon
BE = binding energy
KE = kinetic energy of the ejected electron
Or hv = kinetic energy of the ejected electron
Bohr's Model:-
Bohr given the theory that an electron revolves around the nucleus of an atom in fixed circular orbit without losing any energy ,an electron loses energy or gains energy only when it goes to other energy levels .
The main success of bohr model was in explaining Rydberg formula for spectral emission of hydrogen atom
Heisenberg's Uncertainity Principle:-
It states that it is impossible to determine simultaneously, the exact position and exact momentum (or velocity) of an electron.The product of their uncertainties is always equal to or greater than h/4π.
Schrodinger's Equation:-
Schrodinger's Equation used in describing quantum mechanical behavior and it predicts analytically and precisely the probability of events or outcome.
Quantum Numbers :-
Their are four quantum numbers :-
1)Principal quantum number
2)Azimuthal quantum number
3)Magnetic quantum number
4)Electron spin
Quantum number specifies the size,shape and orientation of an orbital ,three quantum numbers needed to specify an orbital and to specify an electron all four quantum numbers needed.
Nodal surfaces or Nodes :-
The region where this probability density function reduces to zero is called nodal surfaces or simply nodes.
Sheilding effect or screening effect:-
The outer electron experiences less attraction of positive charge of nucleus due to inner electrons ,this effect is called screening effect it increase with increase in Azimuthal quantum numbers.
Aufbau Principle:-
In the ground state of atom the orbital are filled in order of their increaseing energies and the order is as follows:-
Below is the order in which orbitals are filled:-
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s..
Pauli Exclusion Principle :-
No two electron have the same set of four quantum numbers and only two electron may exist in the same orbital and they must have opposite spin
Hund's rule of maximum multiplicity :-
Pairing of electron will not take place in an orbital until the pairing subshell is singly occupied.
Electronic configuration of atoms:-
Arrangement of electrons in different orbitals of an atom.It is represente in two ways given below:-
Orbital diagram:, Each orbital of the subshell is represented by a box and the electron is represented by an arrow (↑) a positive spin or an arrow (↓) a negative spin and sapbdc...etc notation.
Stability of completely filled and half filled subshells :-
Symmetrical distribution of electrons- .completely filled or half filled sub-shells have symmetrical distribution of electrons in them and are more stable
Exchange energy-The two or more electrons with the same spin present in the degenerate orbitals of a sub-shell can exchange their position and the energy released due to this exchange is called exchange energy.The number of exchanges is maximum when the subshell is either half filled or completely filled. As a result the exchange energy is maximum and so is the stability.
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