Structure Of Atom Notes
Atom :-
John Dalton propose that atom is the smallest particle of matter. It contains three subatomic particles name the electron proton and neutron.
Electron :-
electron was discovered as a result of study of the cathode ray by JJ Thomson it name by
Stoney
1. Cathode Ray cause mechanical motion of the small pin-wheel placed in their path. Thus, they possess kinetic energy. Hence they are material particle.
2. the produce from the cathode of a discharge tube and which move away from it at a right angle towards a node in a straight line are called as cathode ray.
3. These produce X-rays when strike with metal and are deflected by electric and magnetic field.
Proton :-
Rutherford discovered proton on the basis of the Anode Ray experiment.
Atomic Number :-
Atomic Number is defined as the number of protons present in the nucleus of an atom of a particular element.
1. Atomic number is represented by Z
2. An atom is electrically neutral. hence the number of protons equal to number of electrons. In other words, atomic number of atom is equal to number of electrons.
Atomic Mass Number :-
The sum of total number of proton and neutron present in the nucleus of an atom is called atomic mass number of that atom.
Neutron :-
Neutron arm neutral particles. It was discovered by Chadwick (1932).
Some uncommon subatomic particles :-
1. Positron - Positive electron discovered by Dirac (1930) and Anderson (1932).
2. Meson - Discovered by you Yukawa (1935) and Kemmer. They are unstable particle and include pi ions.
3. Anti-proton - It is a negative proton produced by Segre and Weilandland (1955).
Isotopes :-
Isotopes are defined as the atom of an element having the same number of proton but different number of neutrons in the nuclei.
Isobars :-
Isobars define as the atom of different element having the same mass number but different atomic number.
Isotones :-
Isotone are defined as the atom of different element having same number of neutrons in the nuclei.
Thomson's Atomic Model
Atom is a positive spear with a number of electron distributed with the spear. It is also known as plum pudding model. It explain neutrality of an atom.
This model could not explain the result of the Rutherford scattering experiment.
Rutherford's Nuclear Model Of Atom
It is based upon alpha scattering particles Rutherford presented that
1. Most part of the atom is empty.
2. Atom possesses a highly dense positively charged centre called nucleus.
3. Entire mass of the atom is concentrated inside the nucleus.
4. Electron revolve around the nucleus in circular orbits.
5. Electron and Nucleus are held together by electrostatic force of attraction.
Drawback of Rutherford Atomic Model
1. According to the electromagnetic theory, when a charged particle are accelerated, the electromagnetic radiation, which comes by electronic motion and orbit continue to shrink, so atom unstable. It does not explain the stability of atom.
2. It does not say anything about the electronic distribution of electrons around nucleus.
Electromagnetic Spectrum :-
The arrangement of different types of electromagnetic radiation in order of increasing wavelength is called as electromagnetic spectrum.
Bohr's Model for Hydrogen Atom
Postulates of Bohr's theory of hydrogen atom
1. electron in hydrogen atom can move on in the nucleus in one of the many possible circular paths of the fix radius and energy. These parts are orbit, stationary state or allowed energy States. These are orbits arranged concentrically around the nucleus in an increasing order of energy.
2. The energy of an electron in the orbit does not change with time. However, electron will move from the lower stationary state to a higher stationary state if and when required amount of energy is absorbed by the electron. The energy change does not take place in a continuous.
Limitation of Bohr's Theory
1. It is unable to explain the spectrum of an atom other than hydrogen like doublets or multielectron atom.
2. It could not explain the ability of an atom to form molecules by chemical bond. Hence it could not predict the shape of the molecule.
3. Bohr's atomic model could not explain the splitting of spectral lines in the presence of magnetic field or electric field.
4. Bohr's atomic model fail to account for final details of the atomic spectrum of hydrogen and observed in sophisticated spectroscopic experiment.
Heisenberg Uncertainty Principle :-
According to the principal it is impossible to specify at any given instant both the momentum and the position of subatomic particle electron.
Quantum number :-
1. Principal Quantum Number :-
It is denoted by n. It tells us about the main share in which a electronic resides. It also gives us an idea about the energy of chef and average distance of the electron from the nucleus.
2. Azimuthal Quantum Number :-
It is denoted by l. It tell about the number of subshells in any main shell. It also represent the angular momentum of an electron and shape of subshell.
3. Magnetic Quantum Number :-
It is denoted by m. Detail about the number of orientation of each subshell.
4. Spin Quantum Number :-
Denoted by s. It indicate the direction of spinning of electron i.e clockwise or anticlockwise.
Electronic Configuration :-
Arrangement of electrons in the space around nucleus in an atom is known as electronic configuration.
Aufbau Principal :-
According to this principle in the ground state of an atom, the electronic occupy the lowest energy orbitals are available to them i.e the orbital are filled in order of increasing value of n + l. For the orbitals having the same value of n+l, the orbital having lower value of n is filled up first.
Pauli Exclusion Principle
It state, no two electron in an atom can have identical set of four Quantum numbers.
Hund's Rule Of Maximum Multiplicity
1. In an atom no electronic repairing takes place in p, f orbital until each orbital of the given subshell contains one electron.
2. The unpaired electrons present in the warriors aur battle of the same session should have to parallel spin.
Method of writing electronic configuration
1. Orbitals method :-
In this, the electron present in the respective orbital are denoted.
2. Shell method :-
In this, the number of electron in each shell is continuously written.
3. Box method :-
In in this method, each orbital is donated by a box and electronic represented by half headed or full headed arrows. An orbital can a maximum of two electrons.
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