1. UNIT 3 ELECTRON CONFIGURATIONS Part B Bohr’s Model of Hydrogen

2. WHAT HAVE WE LEARNED SO FAR? Discharging Tubes The Flame Test The light coming out of the excited atomic entities is very specific to particular element! Results are quite reproducible.

3. ELECTROMAGNETIC RADIATIONS (LIGHTS) COMING OUT OR BEING ABSORBED BY ATOMS INDICATE THAT THERE ARE VERY SPECIFIC ENERGY CHANGES WITHIN THE ATOMIC ENTITIES (ATOMS AND IONS). NO NUCLEAR CHANGES HAVE EVER BEEN OBSERVED INDICATE THAT THE ENERGY CHANGES HAVE TO COME FROM ELECTRONS SURROUNDING THE NUCLEUS.

4. How Come? Classic Model: Electron anywhere it ‘wants’ to be Problems with classic model: E moving through electric field will emit light & from the classic model, emitted light should have differing wavelengths

5. NIELS BOHR (1885 – 1962) Increasing energy with greater distance from nucleus

6. BOHR’S MODEL OF HYDROGEN ATOM Increasing energy Nucleus First-ground Second Third Fourth Fifth-excited } Further away from the nucleus means more energy. There is no “in between” energy Energy Levels

7. quantum – quantity of energy gained or lost by an atom when electrons are excited photon – a quantum of light ground state – lowest energy level of an atom excited state – a heightened state of energy in an atom Electrons of hydrogen circle the nucleus in orbits 1. orbits have a fixed amount of energy in the ground state. 2. orbits are a fixed distance from the nucleus. 3. orbits furthest from the nucleus have the greatest energy. BOHR’S MODEL OF HYDROGEN ATOM

11. Bohr’s Model of Hydrogen Atom Orbits Transitions of e between those orbits involve change in energy Change in energy (E(n2 –n1) has to be accounted for By photons Successful in accounting for most of the H-1 emission/absorption spectral lines BUT only works for H-1