Class 11 chemistry ch 2

CLASS 11 chemistry chapter 2

STRUCTURE OF ATOM 

Class 11 Chemistry CBSE

Atoms:

Atom is the smallest indivisible particle of the matter. Atom is made of electron, proton and neutrons.

PARTICLE

ELECTRON

PROTON

NEUTRON

Discovery

Sir. J. J. Thomson

(1869)

Goldstein (1886)

Chadwick (1932)

Nature of charge

Negative

Positive

Neutral

Amount of charge

1.6 x 10-19Coloumb

1.6 x 10-19Coloumb

0

Mass

9.11 x 10-31kg

1.672614 x 10-27kg

1.67492 x10-27kg

  Electrons were discovered using cathode ray discharge tube experiment.

Nucleus was discovered by Rutherford in 1911.

Cathode ray discharge tube experiment: A cathode ray discharge tube madeof glass is taken with two electrodes. At very low pressure and high voltage,current starts flowing through a stream of particles moving in the tube fromcathode to anode. These rays were called cathode rays. When a perforatedanode was taken, the cathode rays struck the other end of the glass tube atthe fluorescent coating and a bright spot on the coating was developed

Results of Rutherford experiments:

a. Cathode rays consist of negatively charged electrons.

b. Cathode rays themselves are not visible but their behavior can be observed with help of fluorescent or phosphorescent materials.

c. In absence of electrical or magnetic field cathode rays travel in straight linesd. In presence of electrical or magnetic field, behaviour of cathode rays is similar to  that shown by electrons

e. The characteristics of the cathode rays do not depend upon the material of the electrodes and the nature of the gas present in the cathode ray tube.

  Charge to mass ratio of an electron was determined by Thomson. The chargeto mass ratio of an electron as 1.758820 x 1011. C kg-1

  Charge on an electron was determined by R A Millikan by using an oil dropexperiment. The value of the charge on an electron is -1.6 x 10-19C.

  The mass on an electron was determined by combining the results ofThomson’s experiment and Millikan’s oil drop experiment. The mass of anelectron was determined to be 9.1094 x 10-31kg.

Discovery of protons and canal rays:

Modified cathode ray tube experimentwas carried out which led to the discovery of protons.

  Characteristics of positively charged particles:

a. Charge to mass ratio of particles depends on gas from which these originateb. The positively charged particles depend upon the nature of gas present in the cathode ray discharge tube

c. Some of the positively charged particles carry a multiple of fundamental of electrical charge.d. Behaviour of positively charged particles in electrical or magnetic field is opposite to that observed for cathode rays

  Neutrons were discovered by James Chadwick by bombarding a thin sheet of beryllium by α- particles. They are electrically neutral particles having a mass slightly greater than that of the protons.

  Atomic number (Z) : the number of protons present in the nucleus(Moseley1913).              

 Mass Number (A) :Sum of the number of protons and neutrons present in thenucleus.

Thomson model of an atom: 

This model proposed that atom is considered asa uniform positively charged sphere and electrons are embedded in it.An important feature of Thomson model of an atom was that mass of atom isconsidered to be evenly spread over the atom.Thomson model of atom is also called as Plum pudding, raisin pudding orwatermelon model Thomson model of atom was iscarded because it could not explain certainexperimental results like the scattering of α- particles by thin metal foils.

Observations from α- particles scattering experiment by Rutherford:

a. Most of the α- particles passed through gold foil un deflected 

b. A small fraction of α- particles got deflected through small angles 

c. Very few α- particles did not pass through foil but suffered large deflection nearly180o 

Conclusions Rutherford drew from α- particles scattering experiment:

a.  Since most of the α-particles passed through foil undeflected, it means most of the  space in atom is empty

b.  Since some of the α-particles are deflected to certain angles, it means that there is positively mass present in atom

c.  Since only some of the α-particles suffered large deflections, the positively charged mass must be occupying very small space

d.  Strong deflections or even bouncing back of α-particles from metal foil were due to  direct collision with positively charged mass in atom Rutherford's atomic model.

 This model made it clear that the atom consisted of a nucleus concentrated in a very small size.  The nucleus contains protons and neutrons.  Electrons revolve around the nucleus with stabilizers.  Electrons and nuclei are held together by electrostatic forces.

 Disadvantages of the Rutherford Atom model.

 a.  According to Rutherford, the atom model, the electrons, is negative

 The charged particles revolve around the nucleus in fixed orbits.  And therefore

 B.  Phones are accelerating.  According to Maxwell's electromagnetic theory, the charged particle that is subject to the acceleration of electromagnetic radiation must be emitted.  Thus, the electron must be emitted into orbit.  So the orbit must be narrowed.  But this does not happen.  The model does not provide information about how electrons are distributed around the nucleus and what is the energy of those electrons.

  Isotopes.  These are atoms of the same element and have the same atomic number but different mass numbers.  1H1,1H2,1H3 g

  Isobars.  Isobars are different element atoms with the same mass but different atomic numbers.  18AR40 and 20Ca40

  Concurrent types.  These are the types that have the same number of electrons.

 Electromagnetic radiation.

 The rays associated with the electromagnetic and magnetic fields are called electromagnetic radiation.  When an charged particle electrically moves under acceleration, alternating electrical and magnetic fields are produced and transported.  These fields travel in the form of waves.  These waves are called electromagnetic waves or electromagnetic radiation.

 Electromagnetic radiation properties.

 a.  Oscillating electric and magnetic fields oscillate by oscillating charged particles.  These fields are orthogonal to each other, both of which are propagating for wave.

 B.  They do not need a way to travel.  This means that they can even travel in an opaque manner.

 Electromagnetic radiation properties.

 a.  Wavelength: It can be defined as the distance between two adjacent lines or a wavy path, as shown.  It is mentioned in to.

 B.  Frequency (n).  It can be defined as the number of waves that pass through a certain point per second.

 C.  Speed ​​(v).  It is defined as the distance accompanied by the wave.  In a vacuum, all types of electromagnetic radiation travel at the speed of the thesis.  Its value is 3 x 10 8 mS -1.  Marked by

 Dr..  Wave number.  The wavelength is defined as the number of wavelengths per unit of length.

 Speed ​​= frequency x wavelength c = νλ

 Quantum Planck theory

 The emitted energy is emitted or absorbed not continuously but continuously in the form of separate small bundles of "quantitative" energy.  In the case of light, the amount of energy is called the photon.

 o The energy of each km is directly proportional to the radiation frequency, ie E α α or E = h, where h = Planck constant = 6.626 x 10-27 JS.

 o Energy is emitted or always absorbed as an integral part of this urartak.  E = nhυ where n = 1,2,3,4, .....

 His body.  The ideal body that emits and absorbs all frequencies is called the black body.  The radiation from this body is called radiation from the body.

 Photoelectric effect.

 The process of emitting electrons from an accurate section of the metal when the appropriate frequency stroke light is called a photoelectric effect.  Emitted electrons are called light electrons.

 Experimental results were observed in the photoelectric effect experiment

 When a beam of light falls on a metal, the electrons are pushed off immediately.

 The number of electrons emitted is proportional to the light intensity or brightness

 o Threshold frequency (vo).  There is a maximum characteristic frequency for each metal, as no photoelectric effect is observed.  This is called the threshold frequency.

 o If the light frequency is less than the threshold frequency, there is no leakage of electrons, regardless of 

Photoelectric work function (Wo): The minimum energy required to ejectelectrons is called photoelectric work function.Wo= hvo

Energy of the ejected electrons : 

Dual behavior of electromagnetic radiation

The light possesses both particle and wave like properties, i.e., light has dual behavior . whenever radiation interacts with matter, it displays particle like properties.(Black body radiation and photoelectric effect) Wave like properties are exhibited when it propagates(interference an diffraction)

Spectrm :-

When a white light is passed through a prism, it splits into a series ofcoloured bands known as spectrum.

Spectrum is of two types:

(a) Continuous and line spectrum  The spectrum which consists of all the wavelengths is called continuous

spectrum.

(b) line spectrum A spectrum in which only specific wavelengths are present is known as a line spectrum. It has bright lines with dark spaces between them.

  Electromagnetic spectrum is a continuous spectrum. It consists of a range ofelectromagnetic radiations arranged in the order of increasing wavelengths ordecreasing frequencies. It extends from radio waves to gamma rays.

  Spectrum is also classified as emission and line spectrum.

o  Emission spectrum: The spectrum of radiationemitted by a substance that has absorbed energy is called an emissionspectrum.

o Absorption spectrum is the spectrum obtained when radiation is passedthrough a sample of material. The sample absorbs radiation of  certainwavelengths. The wavelengths which are absorbed are missing and comeas dark lines.

   The study of emission or absorption spectra is referred as spectroscopy.

Spectral Lines for atomic hydrogen:

Rydberg equation

R = Rydberg’s constant = 109677 cm-1 

Bohr’s model for hydrogen atom: 

a. An electron in the hydrogen atom can move around the nucleus in a circular path of fixed radius and energy. These paths are called orbits orenergy levels. These orbits are arranged concentrically around thenucleus

b.  As long as an electron remains in a particular orbit, it does not lose or gain energy and its energy remains constant.

c.  When transition occurs between two stationary states that differ inenergy, the frequency of the radiation absorbed or emitted can be calculated

 d.  An electron can move only in those orbits for which its angularmomentum is an integral multiple of h/2π

  The radius of the nth orbit is given byrn =52.9 pm xn2/Z            

  energy of electron in nth orbit is :

Limitations of Bohr’s model of atom: 

a.  Bohr’s model failed to account for the finer details of the hydrogen spectrum.

b.  Bohr’s model was also unable to explain spectrum of atoms containing more than one electron.

Dual behavior of matter:

 de Broglie proposed that matter exhibits dualbehavior i.e. matter shows both particle and wave nature. de Broglie’s relation is

   

Heisenberg’s uncertainty 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.

  

  Heisenberg’s uncertainty principle rules out the existence of definite pathsor trajectories of electrons and other similar particles

Failure of Bohr’s model: 

a. It ignores the dual behavior of matter.

b. It contradicts Heisenberg’s uncertainty principle.

Classical mechanics : is based on Newton’s laws of motion. It successfullydescribes the motion of macroscopic particles but fails in the case ofmicroscopic particles.Reason: Classical mechanics ignores the concept of dual behaviour of matter especially for sub-atomic particles and the Heisenberg’s uncertainty principle.

Quantum mechanics is a theoretical science that deals with the study of themotions of the microscopic objects that have both observable wave like andparticle like properties.

Quantum mechanics is based on a fundamental equation which is calledSchrodinger equation.

Schr .dinger's equation.

 For a system (such as an atom or a molecule whose energy does not change over time), Schrödinger's equation is written as follows:

 When the Schrödinger equation for the hydrogen atom is solved, the solution gives the possible energy levels that the electron can occupy և The corresponding wavelength (s) of the electron is the function (s) associated with each energy level.

 Possible values, only certain solutions are allowed.  Each permissible solution is very important because it corresponds to a certain action.  Therefore, we can say that energy is quantitative.

 Probability density.  Տալիս gives the wavelength.  Ψ Value does not matter.  g2 gives us the area where the electron is most likely to be found.  It's called probability density.

 Orbit.  The space around the nucleus, where the maximum probability of an electron is called an orbit.

 Quantity number:

 There are a number of four quantum numbers that determine energy, size, direction, and orbit.  Only three quantum numbers are required to determine the direction of the electron, all four quantitative numbers are required.

 Basic Quantum Number (n).  Determines the subsoil, determines the size and energy of the orbits

  Azimuth number (l) is the azimuth number.  "L" is also known as orbital angular momentum or subquantum.  to It defines the subcategory, determines the shape of the orbits and the energy of the orbits in multi-block atoms, as well as the basic quantum number եծ the orbital angle

  At the moment, that is, the number of orbits in the subroutine = 2 l + 1. For a given value of n, it can have n values ​​from 0 to n-1.  The total number of submetals in this envelope is equal to the value of n.

 Subclass

 Icons:

 s

 s

 Dr.

 F:

 C.

 "L" value

 0:

 1:

 2

 3:

 4:

 No.

 Run

 1:

 3:

 5:

 7:

 9:

 Magnetic Quantum Number or Orbital Magnetic Quantum Number (ml).  It provides information on the orbital spatial direction of a coordinated standard set of coordinate axes.  It is possible for l, ml = - l, - (l -1), - (l - 2) ... 0,1 ... (l - 2), (l - 1), l for each value

 The rotating number of the electron (ms).  Indicates the direction of rotation of the electron.  It can contain two values: +1/2: -1/2.  +1 / 2 determines the clock և -1 / 2 determines the illegal shift.

  Nodal surfaces or nodes simply.

 The region where the probability density of this probability falls to zero is called node surfaces or just nodes.

  Ial Stellar Ganglia.  Radial ganglion occurs when the intensity of the electron wave's function is zero on a spherical surface of a certain radius.  Rad number of radial nodes = n - l - 1:

  Angular nodes.  Angular nodes occur when the electron probability density wave function is zero in the directions indicated by a given rectangle.  Number of corner nodes = l

  Total number of nodes = n - 1:

 Destructive orbits.  Orbits with the same energy are called orbital layers.  The direction of the orbits is p և d

 Protective effect or display effect.

 Because the electrons are in the inner shell, the electron in the outer shell will not be affected by the entire charge on the nucleus.  Therefore, due to the impact of the examination, the purely positive charge that the electron passes through the nucleus is reduced and is known as the active nuclear charge.  Effective nuclear charge of orbital failure with an increase in the number of azimuths (liters).

 The Obao principle.

 In the terrestrial state of the atoms, the orbits are filled with increasing energies

  n + l Rules-orbitals that have a lower value (n + l) have less energy.  If two orbits have the same value (n + l), an orbit with a lower value of nwill will have less energy.

  The procedure for completing the orbits is as follows:

 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s ...

 Pauli's exclusion principle.

 Two electrons in an atom cannot have the same number of four quantum numbers.  There can only be two electrons may exist in the same orbitaland these electrons must have opposite spin.

Hund’s rule of maximum multiplicity:

Pairing of electrons in the orbitalsbelonging to the same subshell (p, d or f) does not take place until eachorbital belonging to that subshell has got one electron each i.e., it is singlyoccupied.

Electronic configuration of atoms:

Arrangement of electrons in different orbitals of an atom. The electronic configuration of differentatoms can be represented in two ways. a. sapbdc...... notation.

b. 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.

Stability of completely filled and half filled subshells:

a.  Symmetrical distribution of electrons- the completely filled or half filled sub-shells have symmetrical distribution of electrons in them and are more stable.

b.  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.