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Advanced Higher Chemistry

Advanced Higher Chemistry. Unit 1 The Electromagnetic Spectrum. Electromagnetic Radiation. Radiation such as x-rays, microwaves and radio signals is known as electromagnetic radiation.

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Advanced Higher Chemistry

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  1. Advanced Higher Chemistry Unit 1 The Electromagnetic Spectrum

  2. Electromagnetic Radiation • Radiation such as x-rays, microwaves and radio signals is known as electromagnetic radiation. • Electromagnetic radiation can be considered in terms of waves which have wavelengths of between 104 and 10-14 metres. • These waves travel in a vacuum at a constant speed of 3 x 108ms-1. This value is called the velocity and is given the symbol ‘c’.

  3. The Electromagnetic Spectrum At the low energy end, the waves are further apart than the length of a football pitch. At the high energy end, the waves are so tightly packed that they are closer together than the size of an atom.

  4. Electromagnetic Radiation • Electromagnetic radiation can be specified by its wavelength and its frequency. • Wavelength (λ) is the distance between adjacent crests of a wave. It is usually measured in nanometres (nm). 1nm = 10-9m • Frequency (f or Ʋ) is the number of wavelengths that pass a fixed point in one second. It is measured as 1/t and has the units s-1. • s-1 is now more commonly known as Hertz (Hz).

  5. Wavelength and frequency The wavelength of wave A has double the value of wave B. Since both waves travel at the same velocity (3 x 108ms-1) then twice as many wavelengths of wave B will pass every second than wave A i.e. the frequency of wave B is twice that of wave A.

  6. velocity = wavelength x frequency c l f (m s-1) (m) (s-1)

  7. Wavenumber • The wavenumber (⊽) is the number of waves in unit length i.e. the number of waves in 1m or 1cm. • ⊽ = 1 / λ • The units for wavenumber are m-1 or cm-1.

  8. Energy • Electromagnetic radiation can be thought of as waves or as particles of energy known as photons. • These photons have a definite size and therefore a definite amount of energy.

  9. Energy of a Photon • For one photon : Energy = Planck’s x frequency constant E = hf i.e. because h is a constant, E is directly proportional to f or E = hc λ • Planck’s constant = 6.63 x 10-34 J s • 1kJ = 1000J

  10. Energy • For one mole of photons: Energy = Avogadro x Planck’s x frequency constant constant E = L h f or E = Lhc λ

  11. Energy Calculations • The red line in the hydrogen spectrum has a wavelength of 656 nm. Calculate the energy, in kJ mol-1, for one mole of photons. NOTE Because c is given in ms-1, l must be converted to m. • E = Lhc / l = 6.02 x 1023 x 6.63 x 10-34 x 3 x 108 656 x 10-9 = 1.82 x 105 J mol-1 = 182 kJ mol-1

  12. Exercise • Copy worked examples 1.1. and 1.2 from pages 4 & 5 of Advanced Higher Chemistry Calculations. • Complete the problems on pages 6 and 7 using the worked examples to help you. • Complete pages 1 – 3 of your workbook.

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