2. New Way Chemistry for Hong Kong A-Level Book 11 Chapter 4 The Electronic Structure of Atoms

3. New Way Chemistry for Hong Kong A-Level Book 12 Line Spectrum of hydrogen 4.1 The Electromagnetic Spectrum (SB p.93) Fig.4-5(b) continue spectrum

4. New Way Chemistry for Hong Kong A-Level Book 13 The Emission Spectrum of Atomic Hydrogen UVVisible IR 4.1 The Electromagnetic Spectrum (SB p.93)

5. New Way Chemistry for Hong Kong A-Level Book 14 Characteristics of emission spectrum of hydrogen 4.1 The Electromagnetic Spectrum (SB p.83) 1.Discrete lines (discontinuous). Certain frequencies (light) are missing. 2.Intensity and distance between lines decrease as frequency increases. 3.A continuum. 4.More than one series of discrete lines.

6. New Way Chemistry for Hong Kong A-Level Book 15 Bohr’s explanation – the electronic structure 1. An electron in an atom can only exist in certain orbits characterized by definite (quantized) energy levels. 2. An orbit with higher energy is further away from the nucleus. 3.When an electron absorbs energy, it jumps from a lower orbit (of energy E 2 ) to a higher orbit (of energy E 1 ). 4.When this excited electron drop back to lower orbit, the energy emitted as light. Its energy is related to the frequency of light recorded in the emission spectrum by:  E = E 1 - E 2 = h 4.1 The Electromagnetic Spectrum (SB p.85)

7. New Way Chemistry for Hong Kong A-Level Book 16 Bohr’s explanation – Discrete lines 1. As the energy differences between higher and lower energy levels are fixed (quantized), thus discrete lines of fixed frequencies are found in the spectrum. 4.1 The Electromagnetic Spectrum (SB p.85) 2.Energy differences between energy levels get smaller and smaller as moving from lower energy level to higher one.  convergence 3.Intensity of lines decreases Transitions between higher energy levels and lower energy levels are less probable than transition between lower energy levels.

8. New Way Chemistry for Hong Kong A-Level Book 17 Bohr’s explanation – more than one series (not mentioned in textbook) 1.It depends on the lower energy levels that an excited electron can return to. Lyman series: n = x  n = 1 (x = 2, 3, 4, 5 ……..) Balmer series:n = y  n = 2 (y = 3, 4, 5, 6………) 4.1 The Electromagnetic Spectrum (SB p.85)

9. New Way Chemistry for Hong Kong A-Level Book 18 Bohr’s explanation – continuum 4.1 The Electromagnetic Spectrum (SB p.87) Starting line of continuum --- Convergence limit

10. New Way Chemistry for Hong Kong A-Level Book 19 Convergence Limits and Ionization A continuum means energy released by the electron is not restricted to fixed amount anymore. This means the electron is no longer lies on the electron shells of an atom.  convergence limit is the minimum amount of energy required to remove an electron from atom.  ionization  Q.1 b(ii) p. 130 This means the electron is no longer lies on the electron shells of an atom.  convergence limit is the minimum amount of energy required to remove an electron from atom.  ionization  Q.1 b(ii) p. 130 4.1 The Electromagnetic Spectrum (SB p.87)

11. New Way Chemistry for Hong Kong A-Level Book 110 The Uniqueness of Atomic Emission Spectra 4.1 The Electromagnetic Spectrum (SB p.90) Different gases produce different colour: Flame test is based on the emission spectrum of metals.

12. New Way Chemistry for Hong Kong A-Level Book 111 The END