1. The Bohr Model: Orbits and Line Spectra

2. Understand the historical development of the Quantum Mechanical Model of the atom. Describe how a produced line spectra relates to the Bohr diagram for a specific element Additional KEY Terms Ground StateAbsorption Spectra Threshold Energy

4. Bohr (1913) – proposed that spectral lines are light from excited electrons. His equations correctly predicted the structured spectral lines of Hydrogen… Created an equation for energy of an electron at each orbit Restricting electrons to fixed orbits (n) of different quantized energy levels ΔE = -2.18 x 10 -18 JZ2nf2Z2nf2 Z2ni2Z2ni2 _

5. 1.Electrons absorb energy and jump from ground state (its resting state) to a higher unstable energy level (excited state). Free Atom e−e− EMR e−e− Ground State e−e− Excited State Ionization Absorption EMR nucleus > Threshold Energy < Threshold Energy 2. Electron fall to ground state – releasing a photon of energy equivalent to the distance moved. “unstable” is the KEY - electrons are attracted to the nucleus and can’t stay away for long

6. ΔE = E higher-energy orbit - E lower-energy orbit = E photon emitted = hf The difference in energy requirements between orbits determines the “colour” of photon released by the electron

7. ΔE = En f - En i = E photon emitted = hf ΔE = -2.18 x 10 -18 JZ2nf2Z2nf2 Z2ni2Z2ni2 _ Change in energy is released as a photon of EMR Predicts the type of EMR released for any transition

8. ΔE = -2.18 x 10 -18 JZ2nf2Z2nf2 Z2ni2Z2ni2 _ What is the energy of the photon released when an electron drops from n=5 to n=2 in a hydrogen atom? ΔE = -2.18 x 10 -18 J122f2122f2 125i2125i2 _ 1414 1 25 _ ΔE = - 4.58 x 10 -19 J

9. What type of light photon is released when an electron drops from n=5 to n=2 in a hydrogen atom? ΔE = - 4.58 x 10 -19 J c = λƒ E = hf λ 6.91 x 10 14 Hz = 3.00 x 10 8 m/s λ = 4.34 x 10 -7 m ƒ 6.626 x 10 -34 J·s = -4.58 x 10 -19 J ƒ = 6.91 x 10 14 Hz λ = 434 nm

10. 3. Levels are discrete (like quanta) – No in-between. 4. Every jump/drop has a specific energy requirement - same transition, same photon.

11. The size of the nucleus will affect electron position around the atom – and the energy requirements Cl: 17 e - Na: 11 p + 11 e - 17 p + Each element has a unique line spectrum as each element has a unique atomic configuration

12. We only “see” those excited electrons that require and release energy in the visible spectrum

13. Absorption spectrum – portion of visible light absorbed by an element – heating up. Emission spectrum – portion of visible light emitted by that element – cooling down. Notice energy absorbed is the same as energy released

14. CAN YOU / HAVE YOU? Understand the historical development of the Quantum Mechanical Model of the atom. Describe how a produced line spectra relates to the Bohr diagram for a specific element Additional KEY Terms Ground StateAbsorption Spectra Threshold Energy