MES Indian School Doha-Qatar Chemistry Notes 2024-25 PDF

MES INDIAN SCHOOL, DOHA-QATAR NOTES 2024-25 Section : Boys’/Girls’ Date: 30.04.2024 Class & Div. :XI (All divisions) Subject: Chemistry Lesson / Topic: Chapte...

MES INDIAN SCHOOL, DOHA-QATAR NOTES 2024-25 Section : Boys’/Girls’ Date: 30.04.2024 Class & Div. :XI (All divisions) Subject: Chemistry Lesson / Topic: Chapter 2 – STRUCTURE OF ATOM XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Atom :  It is the smallest particle of matter that takes part in a chemical reaction.  Most of the elements are monatomic, oxygen, hydrogen, nitrogen and halogens are diatomic. Phosphorous is tetra atomic and sulphur octa atomic. Sub atomic particles : Electron , Proton and Neutron.  An electron : Discovered by J.J Thomson electron name given by Stony.  Electron is the fundamental particle which carries 1 unit negative charge (1.6 x 10 -19C) and has a mass nearly equal to 1/1837 th of that hydrogen atom(9.11x10-31 kg).  Proton : Discovered by Goldstein  Proton is the fundamental particle which carries 1 unit Positive charge (1.6 x 10 -19 C) and has a mass nearly equal to of that hydrogen atom(1.672× 10–27kg).  Neutron : Discovered by James Chadwick  Neutron is the fundamental particle which carries neutral charge and has a mass nearly equal to that of hydrogen atom(1.672× 10–27kg) Representation of atom : ZXA Where : A is Mass number, Z is Atomic number, X Symbol of atom.  Atomic Number : It is represented by Z. The number of protons present in the nucleus of an atom is called atomic number of an element. It is also known as nuclear charge. For neutral atom : Number of proton = Number of electron For charged atom : Number of electron = Z + (charge on atom}  Mass Number : It is represented by capital A. The sum of number of neutrons and protons is called the mass number of the element. It is also known as number of nucleons because neutron & proton are present in nucleus. A = number of protons + number of neutrons Isotopes : Given by Soddy  They are the atoms of a same element which have the same atomic number (Z) but different mass number(A).   They have same Nuclear charge (Z) but different number of Neutrons (A–Z).  Isotopes have same chemical property but different physical property.  12 13 14 6C 6C 6C F 061, Rev 01, dtd 10th March 2020 Page 1 of 13   e=6 e=6 e=6  p=6 p=6 p=6  n=6 n=7 n=8  Isobars : Given by Aston  They are the atoms of different element which have the same mass number (A) but different atomic number (Z).  They have different number of Electron, Protons & Neutrons , but the sum of number of neutrons & Protons (number of nucleons) remains same. For Eg. 19 K40 20 Ca40 THOMSON'S MODEL OF ATOM :- 'Plum-Pudding model'.  Thomson proposed that an atom consists of a uniform sphere of positive charge in which the electrons are present at some places. RUTHERFORD's MODEL OF ATOM  The positively charged heavy mass, which occupies only a small volume in an atom, is called nucleus. It is supposed to be present at the centre of the atom.  Electrons revolve round the nucleus in closed orbits with high speeds. This model was similar to the solar system, the nucleus representing the sun and revolving electrons as planets. Drawbacks of Rutherford model :  This theory could not explain the stability of an atom. According to Maxwell electron loses it's energy continuously in the form of electromagnetic radiations. As a result of this, the electron should loss energy  at every turn and move closer and closer to the nucleus following a spiral path. The ultimate result will be that it will fall into the nucleus, thereby making the atom unstable.  If the electrons loss energy continuously, the observed spectrum should be continuous but the actual observed spectrum consists of well-defined lines of definite frequencies (discontinuous). Hence, the loss of energy by electron is not continuous in an atom. Electromagnetic waves (EM waves) or Radiant Energy/Electromagnetic radiation It is the energy transmitted from one body to another in the form of waves and these waves travel in the space with the same speed as light ( 3 × 108 m/s) and these waves are known as Electromagnetic waves or radiant energy. Electromagnetic spectrum or EM spectrum : The arrangement of arranging various types of EM waves in order of their increasing frequency or decreasing wave length is called as EM SPECTRUM. Characteristics of Electromagnetic Radiations: F 061, Rev 01, dtd 10th March 2020 Page 2 of 13   All electromagnetic radiations travel with the velocity of light.  These consist of electric and magnetic fields components that oscillate in direction perpendicular to each other and perpendicular to the direction in which the wave is travelling.  The radiant Energy do not need any medium for propagation    A wave is characterized by following six characteristics.  Wavelength (Lambda) : It is defined as the distance between two nearest crest or nearest trough. It is measured in terms of a A° (Angstrom), pm (Picometre), nm (nanometer), cm(centimetre), m (metre) 1Å = 10–10 m, 1 Pm = 10–12 m, 1nm = 10–9 m, 1cm = 10–2m  Frequency (nu ) Frequency of a wave is defined as the number of waves which pass through a point in 1 sec. It is measured in terms of Hertz (Hz ), sec–1 , or cycle per second (cps) 1 Hertz = 1 sec–1 = 1 cps..  Velocity (c) Velocity of a wave is defined as distance covered by a wave in 1 sec.  Wave number ( nu ar) It is the reciprocal of the wave length that is number of wavespresent Demerits of Electromagnetic Radiation ( wave nature) It fails to explain phenomena like black body radiation, photoelectric effect and atomic line spectra. Particle nature of electromagnetic radiation: Black Body Radiation:  An ideal body, which emits and absorbs radiations of all frequencies uniformly, is called a black body and the radiation emitted by such a body is called black body radiation.  An ideal black body is a perfect absorber and perfect emitter of radiation. Planck's Quantum Theory According to Planck's quantum theory :  The radiant energy emitted or absorbed by a body not continuously but discontinuously in the form of small discrete packets of energy and these packets are called quantum.  In case of light, the smallest packet of energy is called as 'photon' but in general case the smallest packet of energy called as quantum.  The energy of each quantum is directly proportional to frequency of the radiation i.e F 061, Rev 01, dtd 10th March 2020 Page 3 of 13   Total amount of energy transmitted from one body to another will be some integral multiple of energy of a quantum. Where n is an integer. Photoelectric Effect:  The phenomenon of ejection of electrons from the surface of metals like K, Rb, Cs etc when a light of suitable frequency strikes on it is called photoelectric effect and emitted electrons are called photoelectrons.  The minimum frequency of the radiation required for photoelectric effect to take place is called threshold frequency  The minimum energy of the radiation required for photoelectric effect to take place is called work function Wo. Conclusions from Photoelectric Effect:  The electrons are ejected from the metal surface as soon as the beam of light strikes the surface.  The number of electrons ejected is proportional to the intensity or brightness of light.  The kinetic energies of the ejected electrons increase with the increase of frequency of the light used. Expression for Photoelectric effect: Kinetic Energy = me is the mass of the electron , v is the velocity associated with the ejected electron, is the frequency , is the threshold frequency and h is the Planck’s constant. Spectrum  A spectrum is a series of coloured bands obtained by the dispersion of light.  A spectrum of white light is a continuous spectrum because the seven colours appear without any gap or one colour merges into another. Cause of Spectrum: When electromagnetic radiation interacts with matter, atoms and molecules may absorb energy and reach to a higher energy state. With higher energy, these are in an unstable state. For returning to their normal (more stable, lower energy states) energy state, the atoms and molecules emit radiations in various regions of the electromagnetic spectrum. Emission and Absorption Spectrum  The spectrum of radiation emitted by a substance that has absorbed energy is called an emission spectrum. I appears as white lines in dark continuous band.  An absorption spectrum is like the photographic negative of an emission spectrum. A continuum of radiation is passed through a sample which absorbs radiation of certain wavelengths. The missing wavelength which corresponds to the radiation absorbed by the matter, leave dark spaces in the bright continuous spectrum. Atomic or Line Spectra: The emission spectra of atoms in the gas phase called line spectra or atomic spectra. Line spectra is not a continuous spectrum because the emitted radiation is identified by the appearance of bright lines in the spectrum.The study of emission or absorption spectra is referred to as spectroscopy.  Line spectrum is called the finger print of an atom because every element has a unique line spectrum F 061, Rev 01, dtd 10th March 2020 Page 4 of 13 F 061, Rev 01, dtd 10th March 2020 Page 5 of 13 g) The frequency of radiation absorbed or emitted when transition occurs between two stationary states that differ in energy by Where E1 and E2 are the energies of the lower and higher allowed energy states respectively. This expression is commonly known as Bohr’s frequency rule. Limitations of Bohr’s Model of Atom  Unable to explain the spectrum of multi-electron atoms (For example – helium atom which contains two electrons).  Unable to explain splitting of spectral lines in electric field (Stark effect) or in magnetic field (Zeeman effect).  Unable to explain the fine spectral lines in H atom.  It could not explain the ability of atoms to form molecules by chemical bonds NOTE: 1. Wave number 2. Energy difference 3. Frequency 4. Energy of an Orbit 5. Radius of an orbit ni is the initial orbit, n2 is the final orbit, Z is the atomic number. Quantum Mechanical Model of the atom In view of the shortcoming of the Bohr’s model, attempts were made to develop a more suitable F 061, Rev 01, dtd 10th March 2020 Page 6 of 13  and general model for atoms. Two important developments which contributed significantly in the formulation of such a model were : 1. Dual behaviour of matter, 2. Heisenberg uncertainty principle The Dual Nature of Matter (The Wave Nature of Electron)  In 1924. a French physicist, Louis De Broglie suggested that if the nature of light is both that of a particle and of a wave, then this dual behavior should be true for the matter also.  According to de Broglie, every object in motion has a wave character and a particle character.  According to De Broglie, the wavelength of an electron is inversely proportional to its momentum. Give the relationship between wavelength (λ) and momentum (p) of a material particle? where m is the mass of the particle, v its velocity and p its momentum. Significance :  Wavelengths of objects having large masses are so short that their wave properties cannot be detected.  Wavelengths of particles having very small masses (electron and other subatomic particles) can be detected experimentally. Q). Why don’t we observe the wave properties of large objects like cricket ball? Because of their large mass, wavelength is small, hence cannot be detected. Heisenberg Uncertainty Principle In 1927, Werner Heisenberg presented a principle known as Heisenberg uncertainty principle which states as : "It is impossible to measure simultaneously the exact position and exact momentum of a body as small as an electron." Significance of Heisenberg’s uncertainty principle  Heisenberg’s uncertainty principle rules out the existence of definite paths or trajectories of electrons and other similar particles.  It is significant only in the case of microscopic particles. F 061, Rev 01, dtd 10th March 2020 Page 7 of 13  Reasons for Failure of Bohr’s model:  It ignores the dual behavior of matter.  It contradicts Heisenberg’s uncertainty principle. Quantum Mechanics The branch of science that takes into account the dual behaviour of matter is called quantum mechanics. Difference between orbit and orbital. Orbit Orbital 1 It is the circular path around the It is the region in space around the nucleus nucleus where electron revolves. where the probability of finding an electron is maximum. 2 It can accomadate a maximum of 2n2 It can accomadate a maximum of two electrons electrons. 3 It is circular in shape Have different shapes. 4 Non-directional Directional 5 Two dimensional Three dimensional 6 Against Heisenberg’s uncertainity In accordance with Heisenberg’s uncertainity principle. principle. QUANTUM NUMBERS :  In an atom, a large no of orbitals are permissible.  These orbitals are designated by a set of 3 numbers known as QUANTUM NUMBERS (principle, azimuthal, magnetic).  These quantum numbers describe energies of electron in an atom, information about shapes and orientation of orbitals.  In order to designate the electron an additional quantum number called as SPINQUANTUM NUMBER is needed to specify spin of the electron. Principal quantum number (n) :  It describes the size of the electron (distance from the nucleolus) and the total energy of the electron.  It represents the main energy level or shell.  It has integral values 1,2,3,4......., etc, and is denoted by K,L,M,N ,etc.  The maximum number of electrons, which can be present in a principal energy shell, is equal to 2n2 Value of n 1 2 3 4 Designation K L M N F 061, Rev 01, dtd 10th March 2020 Page 8 of 13  Azimuthal quantum number (l):  It indicates sub shell –shape and energy  Number of sub shells in a shell = value of n  For a given value of n , l can have values from 0 to (n – 1).  The subshell can be designated as Value of l 0 1 2 3 Designation s p d f lDesignation shape 0 s Spherical 1 p Collection of dumbbell 2 d Collection of double dumb-bells 3 f Complex 4 g Complex n Possible l values Designation 1 o 1s 2 0,1 2s,2p 3 0,1,2 3s,3p,3d 4 0,1,2,3 4s, 4p ,4d, 4f Magnetic quantum number (ml) :  It describes the orientations of the sub shells. Each orientation is called orbital.  It can have values from –l to +l including zero, total (2l + 1) values for each sub shell.  Each value corresponds to an orbital.  The total number of orbitals present in a main energy level is 'n2'. Subshell Its l Number of ml value orientation s 0 2x0+1=1 0 Non directional p 1 2x1+1=3 -1 0, +1 px, py and pz d 2 2X2+1=5 -2-1,0, +1,+2 dxy, dyz, dzx, dx2 – y2, dz2  f 3 2x3+1=7 -3, -2,-1, 0, +1, +2, +3  Sub-shell notation s p d f Number of orbitals 1 3 5 7 Max. electrons 2 6 10 14 Spin quantum number (ms) :  It describes the spin of the electron.  It has values +1/2 and –1/2. (+) signifies clockwise spinning and (–) signifies anticlockwise spinning.,  It indicates each orbital can have two electrons. F 061, Rev 01, dtd 10th March 2020 Page 9 of 13  Boundary Surface Diagrams S subshell P subshell d-subshell Radial node: are nodes present along the axis Node- Radial and Angular Node  The region where the probability of finding the electron is zero is called nodal surface or node.  Radial nodes are present along the axis.  The probability of finding an electron is zero at the plane passing through the nucleus (origin).( Plane bisecting the lobes). This is called angular node.  Total node = n-1; Radial node = n-l-1 ; Angular node = Value of l  For 2P (n=2 l =1) Total nodes = n-1, 2-1=1 ; Angular nodes = l =1 ; Radial nodes = n-l-1, 2-1-1=0 Energy of orbital :  The shielding of outer electrons from the nucleus by the inner electrons is called shielding or screening effect.  The net positive charge experienced by the outer electrons from the nucleus in a multielectron atom is F 061, Rev 01, dtd 10th March 2020 Page 10 of 13  called effective nuclear charge. n +l rule ( Bohr-Bury rule ) :.  Lower the value of (n + l) for an orbital, lower is its energy.  When two orbitals have the same value of (n + l), the orbital with lower value of n will have lowerenergy and it will be filled first. RULES FOR FILLING OF ORBITALS: Aufbau Principle :  Aufbau is a German word and its meaning 'Building up'.  Aufbau principle states that “In the ground state of the atoms, the orbitals are filled in order of their increasing energies”.  Aufbau principle gives a sequence in which various subshell are filled up depending on the relative order of the energies of various subshell.  The sequence in which various subshell are filled is the following Pauli's Exclusion principle :  It states that” No two electrons in an atom can have same values of all four quantum numbers.”  “Only two electrons may exist in the same orbital and these electrons must have opposite spin.” Hund’s Rule of Maximum Multiplicity It States that pairing of electrons in the orbitals belonging to the same subshell (p, d or f) does not take place until each orbital belonging to that subshell has got one electron each i.e., it is singly occupied. Electronic Configuration of Atoms  The distribution of electrons into orbitals of an atom is called its electronic configuration.  The electronic configuration of different atoms can be represented in two ways. F 061, Rev 01, dtd 10th March 2020 Page 11 of 13 Q). Write the electronic configuration of elements from atomic number 1 to 30. Stability of Completely Filled and Half Filled Subshells The half filled ( Cr ) and Completely (Cu) filled orbitals are more stable due to highexchange energy and symmetrical distribution of electrons. QUESTIONS - NUMERICALS F 061, Rev 01, dtd 10th March 2020 Page 12 of 13 QUESTIONS 1. Define the following terms: 1. Electromagnetic radiation 2. Electromagnetic Spectrum 3. Black Body radiation 4. Photoelectric Effect 5. Shielding Effect 6. Effective nuclear charge 7. Atomic spectrum 8. Threshold frequency 2. Write the difference between the following: 1. Absorption and emission spectrum 2. Zeeman and stark effect 3. Orbit and orbital 4. Radial and angular node 3. State the following Principles: 1. Heisenberg’s Uncertainty principle 2. Aufbau Principle 3. Pauli’s Exclusion principle 4. Hund’s rule of maximum multiplicity. 5. Bohr- Bury’s rule. 6. Bohr Frequency rule 4. Account for the following. 1. Atomic spectrum is known as the finger print of an atom. 2. Wave property of large objects like cricket ball cannot be detected. 3. Electronic configuration of chromium and copper shows extra stability. 5. Explain Planck’s quantum theory. 6. Explain de-Broglie relation. 7. Write the expected and actual configuration od Cr and Cu? 8. What is the the significance of de-broglie relation and Heisenberg’s uncertainty principle? 9. What are the limitations of Bohr model of an atom.? 10.What is balmer series? In which spectral region it lies? ************************************************** F 061, Rev 01, dtd 10th March 2020 Page 13 of 13