The Bohr Theory

The Bohr Theory

1. ·

   • Bohr thought that any model of the atom must explain: A. Why the emission line spectra of the elements are characteristic to that element. and B. Why the emission spectra are line rather than continuous.

2. Electrons orbit the nucleus in fixed paths called energy levels.

3. The energy in a particular energy level is quantised.

   • Atoms in one particular energy level cannot gain or lose energy.
     • The ground state is one in which the electrons in the atom of that element occupy the lowest available energy levels.
       • Atoms normally exist in the ground state.

4. The excited state of an atom is one in which the electrons of that atom occupy higher energy levels than those available in the ground state.

   • When an an atom is provided with heat or electricity.
     • When electrons drop from the higher energy levels to lower they emit a photon of light.
       • The frequency of the light emitted is : E2-E1=hf
         • h= plancks constant and f = the frequency of light.
           • The set of electron transitions that produce a line spectrum that we can see with the naked eye is called the Balmer Series.
             • Orbits are denoted by n=1,etc.
             • An energy level is the fixed amount of energy an atom in an electron may have.
         • The energy absorbed = E2-E1
         • The energy difference is proportional to the light emitted.

5. Some atoms of the same element react differently to others and have different electron transitions.

   • move to second level/third level

6. NB: Each element has a unique line spectrum because each element has a different number and arrangement of electrons