Pre-IB/Pre-AP CHEMISTRY

1. Pre-IB/Pre-AP CHEMISTRY Chapter 4 – Arrangement of Electrons in Atoms

2. Section 1 Objectives • Be able to define: electromagnetic radiation, electromagnetic spectrum, wavelength, amplitude, frequency, photoelectric effect, quantum(pl. quanta), photon, ground state, excited state, line emission spectrum, continuous spectrum, energy level.

3. Section 1 Objectives • Be able to explain the mathematical relationship between speed, wavelength, and frequency of a wave. • Be able to describe what is meant by the wave-particle duality of light. • Be able to discuss how the photoelectric effect and the line emission spectrum of hydrogen lead to the development of the atomic model.

4. Section 1 Objectives • Be able to describe the Bohr model of the atom.

6. Wave • A wave is a method of transferring energy. This transfer does not require matter as a medium.

7. Wave • Some waves travel through matter (sound, water waves, etc.).

8. Wave • Some waves do not require matter and can travel through empty space (light).

9. Wave Properties • Waves can be described by their wavelength, amplitude, and frequency.

10. Wavelength • A crest is the highest point on a wave. • A trough is the lowest point on a wave. Crest Trough

11. Wavelength • Wavelength is simply the length of a wave. It is the distance between two crests or two troughs. • Wavelength is measured in m, mm, or nm. Wavelength Crest Trough

12. Amplitude • Amplitude is simply the height of a wave. It is the distance between the crest and trough of a wave. • Amplitude is measured in units of distance. Amplitude

13. Frequency • Frequency is the number of waves passing a given point in a given time. • Frequency describes the energyof a wave.

14. Frequency • Frequency describes the energy of a wave: the higher the frequency, the greater the energyof that wave.

15. Frequency • Frequency is measured in hertz or cycles per secondor vibrations per second or 1/sec or sec-1 - they all mean the same thing.

16. Frequency • As the wavelength increases, frequency decreases. This is called an inverse relationship.

17. Wave Properties • Wavelength and amplitude give waves their distinctive properties. For example, the loudness of a sound wave is its amplitude, the color of visible light is its wavelength.

18. Types of waves • Electromagnetic waves do not require a medium or matter in order to travel. Light is an example.

19. Light • Light is an electromagnetic wave. • Visible light is a small part of the electromagnetic spectrum that humans are able to see.

20. Light • The electromagnetic spectrum consists of different kinds of light of different wavelengths.

21. EM Spectrum

22. EM Spectrum

23. EM Spectrum

24. EM Spectrum

25. EM Spectrum

26. EM Spectrum

27. EM Spectrum

28. Light Interactions • White light is light consisting of all colorsof visible light. These colors are visible in a rainbow or through a prism.

29. Velocity • The velocity of a wave is a product of its frequency and wavelength. v= fl v = velocity f = frequency l = wavelength

30. Velocity • The velocity of light through a vacuum(c) is about 3.0 x 108 m/sec. It is slightly slower through matter.

31. Photoelectric Effect • Photoelectric effect refers to the emission of electrons from a metal when light shines on the metal.

32. Photoelectric Effect • It was found that light of a certain frequency would cause electrons to be emitted by a particular metal. Light below that frequency had no effect.

33. Emission Spectra • If an object becomes hot enough it will begin to emit light.

34. Emission Spectra • Max Planck suggested that hot objects emit light in specific amounts called quanta (sing. quantum).

35. Emission Spectra • Planck showed the relationship between a quantum of energy and the frequency of the radiation. Equantum= hf Equantum= energy of a quantum in joules h = Planck’s constant f = frequency

36. Wave-Particle Duality • Einstein later said that light had a dual nature – it behaved as both a particle and a wave.

37. Wave-Particle Duality • Each particle of light, Einstein said, carries a particular quantum of energy.

38. Wave-Particle Duality • Einstein called the “particles” of light photons which had zero mass and carried a quantum of energy. The energy is described as: Ephoton= hf

39. Photoelectric Effect • Einstein explained photoelectric effect by saying in order for an electron to be ejected from a metal, the photon striking it must have enough energy to eject it.

40. Attraction • Different metals have stronger attraction for their electrons than other. Therefore, some must absorb more energy than others to emit electrons.

41. Ground State • The lowest energy state of an atom is called its ground state.

42. Excited State • When a current is passed through a gas at low pressure, the atoms become “excited.”

43. Excited State • Atoms in an excited state have a higher potential energy than their ground state.

44. Excited State • An “excited” atom will return to its ground state by releasing energy in the form of electromagnetic radiation.

45. Emission Spectra • Elements will emit radiation of certain frequencies. This reflects the energy states of its electrons and is called a bright-line or emission spectrum.

46. Emission Spectra • The emission spectrum of an element is like its “fingerprint”. Sodium Helium Mercury

47. Energy Levels • Studying the emission spectrum of hydrogen lead Niels Bohr to the idea of energy levels.

48. Energy Levels • The spectrum Bohr and others observed was the result of excited electrons releasing photons as they returned to their ground states.

49. Energy Levels • The difference in the energy of photons was reflected in the different frequencies of light they observed.

50. Section 2 Objectives • Be able to define: diffraction, interference, Heisenberg Uncertainty Principle, Quantum Theory, quantum numbers, principal quantum number, angular momentum quantum number, magnetic quantum number, spin quantum number. • Be able to distinguish between the Bohr model and the quantum model of the atom.