CHAPTER 2 ATOMIC STRUCTURE 2.1 Bohr's atomic model 2.2 Electronic configuration

Bohr’s Postulates: BOHR ATOMIC MODEL Niels Henrik Bohr ( ). Danish physicist.. Electron move in _fixed amount of energy in an orbital of an atom These orbitals is known as energy levels or quantum levels.  The energy of an electron is quantised:  Electron has fixed amount of energy

The light emitted with a discrete amount of energy is called photon : When electron absorbs energy, it will move from ground state to higher energy level that is called excited stated  The excited state is unstable, then electron will lose energy and fall back to the lower energy levels  These energy will be radiated as light. Bohr’s Postulates:

Each photon of light has a fixed frequency,  The energy of the light emitted or absorbed is the difference in the energy between two electron shells Bohr’s Postulates:

n =1n = 2n = 3n = 4 Electron is excited from lower to higher energy level. A specific amount of energy is absorbed  E = h = E 1 -E 3 (+ve) Electron falls from higher to lower energy level. A photon of energy is released.  E = h = E 3 -E 1 (-ve)

Quantum Staircase Quantum Energy: Energy is not continuous but exists in a packet of energy with a definite value

Energy level diagram for the hydrogen atom Potential energy n = 1 n = 2 n = 3 n = 4 n =  Energy released Energy absorbed

Regions of the Electromagnetic Spectrum

LINE SPECTRUM (atomic spectrum)  A spectrum consists radiation of discrete lines with a specific wavelength or frequency.  produced by excited atoms and ions as the electrons fall back to a lower energy level. composed of only a few wavelengths giving  composed of only a few wavelengths giving a series of discrete line separated by blank a series of discrete line separated by blank areas areas

A sample of gaseous H 2 is dissociated into H atoms and excited by an electric discharged The emitted light passes through a slit and a prism, which the light disperse into individual wavelength The light does not create a continuous spectrum  it creates a line spectrum FORMATION ATOMIC SPECTRA

n = 1 n = 2 n = 3 n = 4 n = 5 n =  Energy Energy absorbed by the atom causes the Electron to move from a lower-energy to a higher-energy state. excited state  very unstable. FORMATION OF LINE SPECTRUM fall back to lower energy  radiate energy (photons) emitted in the form of light

n = 1 n = 2 n = 3 n = 4 n = 5 n =  Lyman Series Emission of photon Line spectrum E Energy FORMATION OF LINE SPECTRUM Fall back to lower energy levels, radiant energies (photons) are emitted in the form of light

FORMATION OF LINE SPECTRUM n = 1 n = 2 n = 3 n = 4 n = 5 n =  Emission of photon Line spectrum Balmer Series E Energy

Seriesnfnf nini Spectrum region Lyman12,3,4,…Ultraviolet Balmer23,4,5,…Visible Paschen34,5,6,…Infrared Brackett45,6,7,...Infrared Pfund56,7,8,…Infrared VARIOUS SERIES IN ATOMIC HDROGEN EMISSION

H(g)  H + (g) + e  E = ? n f = ∞n i = 1 Ionization energy (IE) : IONIZATION ENERGY OF H ATOM Unit: kJ/mol Ionised when electron is removed from : Ionised when electron is removed from : to

1 1 st line Convergent limit FINDING IONISATION ENERGY EXPERIMENTALLY:   Ionisation energy is determined by detecting the wavelength of the convergence point