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- 1. STRUCTURE OF ATOM Chapter 4 Presented by: Freya Cardozo
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- 3. DISCOVERY OF SUBATOMIC PARTICLES • There are three subatomic particles i.e electron, proton and neutron • Proton and neutron are present in the atomic nucleus and together are called nucleons • Electrons are present in the extranuclear part of an atom Presented by: Freya Cardozo
- 4. DISCOVERY OF ELECTRON • By J.J Thompson • Used the cathode ray tube • Discovered the cathode rays • Very small negatively charged particles • 1837 times lighter than the hydrogen atoms • Present in all Presented by: Freya Cardozo
- 5. CATHODE RAY TUBE Presented by: Freya Cardozo
- 6. RUTHERFORD EXPERIMENT Presented by: Freya Cardozo
- 7. RESULTS Presented by: Freya Cardozo
- 8. DISCOVERY OF PROTON • From Rutherford’s scattering exp the subatomic particle i.e proton was discovered • Ernest Rutherford found in the experiment of scattering of α-particles by thin gold foil that a few α-particles bounce back. • From this he inferred the presence of massive and positively charged nucleus inside the atom Presented by: Freya Cardozo
- 9. • when the alpha particle bombarded the nitrogen atom a hydrogen atom was produced • Similar dismutation produced H atoms the hydrogen nucleus must be contained inside nuclei of all the elements. Hence, the hydrogen nucleus was renamed as proton. Presented by: Freya Cardozo
- 10. DISCOVERY OF NEUTRON • Ernest Rutherford 1920 to account for the disparity in atomic number and atomic mass of an element. • In the year 1932, James Chadwick measured velocity of protons knocked out from paraffin by an unidentified radiation from beryllium • From that he determined the mass of the particles of the unidentified neutral radiation which came out to be almost the same as that of a proton. He named this particle as ‘neutron’ Presented by: Freya Cardozo
- 11. ATOMIC NUMBER & MASS NO. • The number of protons in the nucleus is chemical identity of an element. This number is called as atomic number (Z) • Atomic number (Z) = Number of protons=Number of electron • The total number of protons and neutrons, that is nucleons, in an atom is called its atomic mass number (A). • Mass number (A) = Number of protons (Z)+ Number of Neutrons (N) • Therefore A = Z + N N = A - Z Presented by: Freya Cardozo
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- 13. BATAO BATAO! Presented by: Freya Cardozo
- 14. • In case of the nuclide 18 40 Ar • A = 40 and Z = 18 • Number of protons = number of electrons = Z = 18 and number of • neutrons N = A – Z = 40 - 18 = 22 Presented by: Freya Cardozo
- 15. ISOTOPES • All the isotopes of an element have the same number of protons but different number of neutrons in their nuclei • Same – atomic number • Different- mass number • Isotopes are of same element • Elements can have one isotope or many • Eg. 18 9 F Presented by: Freya Cardozo
- 16. ISOBARS • The atoms of different elements having the same mass number but different atomic numbers are called isobars. • Same mass number • different atomic number • Isobars are different elements Presented by: Freya Cardozo
- 17. SOLVE • Three elements Q, R and T have mass number 40. Their atoms contain 22, 21 and 20 neutrons, respectively. Represent their atomic composition with appropriate symbol. Presented by: Freya Cardozo
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- 19. ISOTONES • The atoms of different elements having same number of neutrons in their nuclei are called isotones • Same number of neutrons Presented by: Freya Cardozo
- 20. DRAWBACKS OF RUTHERFORD’S ATOMIC MODEL • Rutherford the negatively charged e-s revolve around the nucleus. This is an accelerated motion + continuous change in velocity because of changing direction • According to the electromagnetic theory of Maxwell charged particles emit electromagnetic radiations • The orbit will gradually shrink • Thus, an electron orbiting about the nucleus would follow a spiral path to the nucleus. • Fall into the nucleus Unstable atom Presented by: Freya Cardozo
- 21. DRAWBACK • Does not describe the distribution of electrons around the nucleus and their energies. Presented by: Freya Cardozo
- 22. BOHR’S ATOMIC MODEL • Bohr utilized results obtained from studies to give model • The results were:- 1. Wave particle duality of electromagnetic radiation Light or electromagnetic radiation behave as both particles and as waves During, Propogation waves interaction with Matter Particles(photons) Presented by: Freya Cardozo
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- 24. PARAMETERS Wavelength (λ) : The distance between two consecutive crests or troughs is called wavelength. • It is represented by the symbol λ which is a greek letter (lambda). • The SI unit for wavelngth is metre (m). Frequency (ν) : The number of waves that pass a given point in one second is called frequency. • It is represented by the greek letter nu, (ν). • The SI unit of frequency is Hertz (Hz or s-1). Presented by: Freya Cardozo
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- 26. Wavenumber (ν) : Wavenumber is the number of wavelengths per unit length. • Wavenumber is represented by the symbol (nu bar) (ν) . • The commonly used unit for wavenumber is reciprocal centimeter (cm-1),while the SI unit is m-1. • Wavenumber is related to the wavelength by an expression ν =1/λ Amplitude (A): Amplitude of a wave is the height of the crest. • Square of the amplitude denotes the intensity of the radiation. Presented by: Freya Cardozo
- 27. SPEED OF LIGHT • In vacuum, the speed of all the types of electromagnetic radiation is the same, which is • C= 3.0 × 108 m s-1 Presented by: Freya Cardozo
- 28. RELATION BETWEEN Λ, Ν, C • wavelength ( λ ),frequency (ν ) and the speed of light (c) c = ν λ Presented by: Freya Cardozo
- 29. KARO CHALO • Visible light has wavelengths ranging from 400 nm violet) to 750 nm (red). Express these wavelengths in terms of frequency (Hz).(1 nm = 10-9 m) Presented by: Freya Cardozo
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- 31. PARTICLE NATURE • Plank gave the name ‘quantum’ to the smallest quantity of energy that can be emitted or absorbed in the form of electromagnetic radiation. • The energy (E) of one quantum of radiation is proportional to its frequency (ν) and given by E = hν • The proportionality constant ‘h’ is called Plank’s Constant. Later its value was found out to be 6.626 × 10-34 J s. Presented by: Freya Cardozo
- 32. SOLVE • Parameters of blue and red light are 400 nm and 750 nm respectively. Which of the two is of higher energy ? • E=hv c = ν λ • Energy is inversely proportional to wavelength Presented by: Freya Cardozo
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- 34. LINE EMISSION SPECTRUM OF HYDROGEN • When substance is irradiated absorb radiation excited gives energy in the form of radiation. • The recorded spectrum of this radiation is called as emission spectrum Presented by: Freya Cardozo
- 35. • When electric discharge is passed through gaseous hydrogen, it emits radiation • the hydrogen emission spectra was recorded in different regions of electromagnetic radiation. • The spectra were not continuous and comprised of a series of lines coressponding to different frequencies Presented by: Freya Cardozo
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- 38. • Balmer gave this formula • 109677 is a constant called as Rydberg’s constant • Here n is the number of orbital Presented by: Freya Cardozo
- 39. BOHR’S POSTULATES 1. The electron in the hydrogen atom can move around the nucleus in one of the many possible circular paths of fixed radius and energy. These paths are called orbits, stationary states or allowed energy states. These orbits are arranged concentrically around the nucleus in an increasing order of energy. Presented by: Freya Cardozo
- 40. 2. The energy of an electron in the orbit does not change with time. However, the electron will move from a lower stationary state to a higher stationary state if and when the required amount of energy is absorbed by the electron.Energy is emitted when electron moves from a higher stationary state to a lower one. The energy change does not take place in a continuous manner. Presented by: Freya Cardozo Absorb energy: e- move to L to H Emission: e- moves from H to L
- 41. 3. The frequency of radiation absorbed or emitted when transition occurs between two stationary states that differ in energy by ΔE is given by the following expression Where, E1- energies of the lower state E2 - energies of higher state. h - Planck’s constant This expression is commonly known as Bohr’s frequency rule. Presented by: Freya Cardozo
- 42. 4. The angular momentum (L) of an electron in a given stationary state can be expressed as m= mass of particle, v= velocity of particle, r= radius of atom n= number of shell/ orbit from the nucleus Thus, an electron can move only in those orbits for which its angular momentum is integral multiple of h/2π. Thus only certain fixed orbits are allowed here Presented by: Freya Cardozo
- 43. BOLO? Presented by: Freya Cardozo
- 44. RESULTS OF BOHR’S MODEL Principle quantum number- The stationary states for electrons. A.k.a orbitals n=1,2,3… Radii of the stationary states For H n=1 and a0=52.9 pm. Thus radius for stationary orbital for hydrogen is 52.9 pm. This is called BOHR’S radius Energy of stationary orbital, RH = Rydberg’s constant= 2.18 × 10-18 J Presented by: Freya Cardozo
- 45. Why –ve sign in the formula?? The negative sign means that the energy of the electron in the atom is lower than the energy of a free electron at rest. Presented by: Freya Cardozo
- 46. For atoms other than hydrogen the energy of the orbital and radius can be calculate using , Presented by: Freya Cardozo
- 47. Velocities of electrons can also be calculated from the Bohr theory. Qualitatively it is found that the magnitude of velocity of an electron increases with increase of Z and decreases with increase in the principal quantum number n. Presented by: Freya Cardozo
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- 50. LIMITATIONS/DEMERITS OF BOHR’S MODEL Bohr’s atomic model failed to account for finer details of the hydrogen atom spectrum observed in sophisticated spectroscopy experiments. Bohr model was unable to explain the spectrum of atoms other than hydrogen Presented by: Freya Cardozo
- 51. Bohr theory could not explain the splitting of spectral lines in the presence of a magnetic field (Zeeman effect) or electric field (Stark effect). Presented by: Freya Cardozo
- 52. Bohr theory failed to explain the ability of atoms to form molecules by chemical bonds. Presented by: Freya Cardozo
- 53. Presented by: Freya Cardozo An atom of an element contains 29 electrons and 35 neutrons. Deduce a.the number of protons b. the electronic configuration of that element CAN YOU DO IT?
- 54. REASONS FOR FAILURE OF BOHR’S ATOMIC MODEL • Wave nature – De-Broglie’s hypothesis • Heisenberg’s uncertainty principle Presented by: Freya Cardozo
- 55. DE-BROGLIE’S HYPOTHESIS • In Bohr model – e- is shown as a charged particle moving in well defined circular orbits about the nucleus. • In contrast to this de Broglie proposed that matter should exhibit a dual behaviour, that is,both particle and wave like properties. • This means that electron should have momentum, p, a property of particle as well as wavelength, λ, a property of wave. • He gave the following relation between λ and p of a material particle Presented by: Freya Cardozo
- 56. HEISENBERG UNCERTAINTY PRINCIPLE Presented by: Freya Cardozo • It is impossible to determine simultaneously, the exact position and exact momentum (or velocity) of an electron • Δx is the uncertainty in position and Δpx (or Δvx) is the uncertainty in momentum
- 57. SOLVE If an element ‘X’ has mass number 11 and it has 6 neutrons, then write its representation. Name the element that shows simplest emission spectrum. Presented by: Freya Cardozo
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- 61. SCHORDINGER EQUATION Presented by: Freya Cardozo Schordinger equation or wave equation is written Here, H is a mathematical operator called Hamiltonian, ψ (psi) is the wave function and E the total energy of the system
- 62. QUANTUM NUMBER • Solving this equation, a set of three quantum numbers characteristic of the quantized energy levels and the corresponding wave functions are obtained. • These are : 1. Principal quantum number n 2. Azimuthal quantum number l 3. Magnetic quantum number ml • George Uhlenbeck and Samuel Goudsmit (1925) who proposed the presence of the fourth quantum number called 4. Electron spin quantum number ms Presented by: Freya Cardozo
- 63. PRINCIPLE QUANTUM NUMBER • n the values can be 1,2,3.. • The value of n increases as we go from the nucleus to outermost orbits • Atomic orbitals having same value of n belong to same shell • With increase of n the number of allowed orbitals is given by n² Presented by: Freya Cardozo
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- 65. AZIMUTHAL QUANTUM NUMBER • Also called subsidiary quantum number • represented by l • Same value of n, different l Indicate the subshell • The number of subshells equal to the number of shells • Values for l range from 0 to (n-1) (n-1) 0 s 1 p 2 d 3 f Presented by: Freya Cardozo
- 66. MAGNETIC QUANTUM NUMBER • Represented by m • Gives the relative spatial orientation of the orbitals in a given subhell • Values of m= (2l+1) • Orientation -l to +l • For s, l=0, m=1 only one possible orientation spherical • For p,l=1,m=3 there rare three possible orientation Px,Py,Pz • For d, • For f, Presented by: Freya Cardozo
- 67. ELECTRON SPIN Q.N • Representation ms • Gives the spin if electron in an orbital • There are two possibilities 1. +1/2 clockwise arrow pointing upward 2. -1/2 Anticlockwise arrow pointing downward • An orbital can accommodate maximum two electrons and they must have opposite spins Presented by: Freya Cardozo
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- 69. SHAPES Presented by: Freya Cardozo
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- 74. SOLVE How many orbitals make the N shell? What is the subshell wise distribution of orbitals in N shell? Presented by: Freya Cardozo
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- 77. An atom has 2 electrons in its 4s orbital. Write the values of the 4 quantum numbers for each of them Presented by: Freya Cardozo
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- 79. PAULI’S EXCLUSION PRINCIPLE • “No two electrons in an atom can have the same set of four quantum numbers.” • Another way to state this Pauli exclusion principle is: “Only two electrons can occpy the same orbital and they must have opposite spins.” There are • only two values that ‘ms’ can which are +1/2 and -1/2. An orbital thus can accommodate only two electrons with opposite spins, so that the fourth quantum number is different for two occupying electrons. • These two electrons with opposite spins occupying the same orbital are called an electron pair. Presented by: Freya Cardozo
- 80. Presented by: Freya Cardozo For He (Z=2) write the 4 quantum numbers for all the electrons
- 81. • There are two methods of representing electronic configuration: Presented by: Freya Cardozo
- 82. ORBITAL NOTATION • In the orbital notation method, a shells is represented by the principal quantum number followed by respective symbol of a subshell and number of electrons occupying that subshell being written as super script on right side of the symbol Presented by: Freya Cardozo
- 83. ORBITAL DIAGRAM • In the orbital diagram method each orbital in a subshell is represented by a box and the electron represented by an arrow (↑ for up spin and ↓ )for low spin) placed in the respective boxes. Presented by: Freya Cardozo
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- 85. AUFBAU’S PRINCIPLE • Aufbau’ is a German word meaning ‘building up’. • The building up of orbital means filling up of orbitals with electrons in the ground state of an atom • Explains the order in which electrons are to be filled in the orbitals Presented by: Freya Cardozo
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- 87. DEGENARTE ORBITS • Those orbits that have the same energy are said to be degenerate • Eg. The 3 sub orbitals px, py and pz have same energy thus are said to be degenrate Presented by: Freya Cardozo
- 88. (N+L) RULE Why according to Aufuab’s rule at some place the 4s is filled first and then 3d? 3rd shell comes before the 4th, then why is this order followed to fill electrons? This is explainedby n+l rule • The lower the sum (n+ l) for an orbital, the lower is its energy. Thus, it will be filled first • If two orbitals have the same (n + l) values then orbital with the lower value of n is of lower energy. This is called the (n + l) rule. Presented by: Freya Cardozo
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- 90. DO IT YOURSELF 1. N (Z=7) 2. Ne(Z=10) 3. Al(Z=13) 4. Ca(Z=20) 5. Kr(Z=36) 6. Zn(Z=30) 7. V(Z=23) 8. S(Z=16) 9. Ge(Z=32) 10. Ag(Z=47) Presented by: Freya Cardozo
- 91. PRACTISE • An atom of an element contains 29 electrons and 35 neutrons. Deduce • the number of protons • the electronic configuration of that element Presented by: Freya Cardozo
- 92. WRITE THE E.C FOR • Chromium Cr (Z=24) • Copper Cu (Z=29) Presented by: Freya Cardozo
- 93. BUT IT BEHAVES ANOMALOUSLY ELEMENT EXPECTED E.C OBSERVED E.C CHROMIUM (Z=24) 1s2 2s2 2p6 3s2 3p6 4s2 3d4 1s2 2s2 2p6 3s2 3p6 4s1 3d5 COPPER (Z=29) 1s2 2s2 2p6 3s2 3p6 4s2 3d9 1s2 2s2 2p6 3s2 3p6 4s1 3d10 Presented by: Freya Cardozo WHY SO???
- 94. HUND’S RULE Hund’s rule of maximum multiplicity • “Pairing of electrons in the orbitals belonging to the same subshell does not occur unless each orbital belonging to that subshell has got one electron each.” Presented by: Freya Cardozo
- 95. Hund’s rule regarding stability • Half-filled and fully filled set of degenerate orbitals has extra stability Presented by: Freya Cardozo
- 96. BATAO KU! • The electronic configuration of oxygen is written as 1s2 2s2 2px 2 2py 1 2pz 1 and not as 1s2 2s2 2px 2, 2py 2 2pz 0, Explain. Presented by: Freya Cardozo
- 97. CONDENSED ELECTRONIC FORMULA Presented by: Freya Cardozo • Use the noble gases to shorten the formula • ‘K (Z = 19) is , 1s2 2s2 2p6 3s2 3p6 4s1 • Ar (Z = 18) is 1s2 2s2 2p6 3s2 3p6 • Condensed formula for ‘K: [Ar] 4s1.
- 98. HOMEWORK • Write condensed orbital notation of electonic configuration of the following elements: • a. Lithium (Z=3) • b. Carbon (Z=6) • c. Oxygen (Z=8) • d. Silicon (Z=14) • e. Chlorine (Z=17) • f. Calcium (Z=20) Presented by: Freya Cardozo
- 99. ISOELECTRONIC SPECIES • Atoms and ions having the same number of electrons are isoelectronic. The electronic configuration of the isoelectronic species is the same Presented by: Freya Cardozo
- 100. QUESTION • Identify from the following the isoelectronic species: • Ne, O2-, Na+ • OR • Ar, Cl2-, K⊕ Presented by: Freya Cardozo