1. Chapter 5: Electrons in Atoms

2. Why focus on electrons? Scientists wanted to know why certain elements behaved similarly to some elements and differently to others Reactivity When heated with a flame

3. Light as Waves Visible light is a type of electromagnetic radiation electromagnetic radiation - a form of energy that exhibits wavelike behavior as it travels through space

4. Wave Diagram http://www.bing.com/images/search?q=diagram+of+a+wave&qpvt=diagram+of+a+wave&FORM=IGRE&adlt=strict#view=detail&id=0E35D2E3DCCE58065D42744F87E2 F1E50CDF5CE8&selectedIndex=3

6. Electromagnetic Spectrum Raging Martians Invaded Venus Using X-Ray Guns LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY

7. Frequency and wavelength are INVERSELY related - as one goes up, the other goes down c:speed of light (3.00  10 8 m/s) :wavelength (m, nm, etc.) f:frequency (Hz) c = f

8. What is the frequency of light that has a wavelength of 680. nm?

9. What is the wavelength of light with a frequency of 4.27 x10 18 hertz?

10. Turn to your partner and summarize… State the relationship between the energy and frequency of electromagnetic radiation. Answer: frequency and energy are directly related, when one goes up, the other goes up, too What are the only differences between the types of electromagnetic radiation on the electromagnetic spectrum? Answer: frequencies and wavelengths of the waves

11. Light as Particles In the early 1900’s, German physicist Max Planck was trying to understand why some substances change color when heated.

12. What Max thought As the substance is heated, its energy changes in specific amounts called quanta Quantum: the minimum amount of energy that can be gained or lost by an atom The amount of energy that can be emitted by a substance is directly proportional to the frequency of the radiation given off. If something is heated, the energy is increased and different frequencies of light are given off (different colors).

13. http://www.michaelbrown.org/HTML/Quantum.htm

14. Einstein’s Contribution Observed the photoelectric effect Concluded - light has properties of both waves and particles “wave-particle duality” Photon - particle of light that carries a quantum of energy C. Johannesson

15. The Photoelectric Effect Electrons (called photoelectrons) are emitted from a metals surface when light of a certain frequency shines on the surface

16. Energy of light is: - directly related to the frequency of the light - inversely related to the wavelength. - As frequency, energy - As wavelength, energy Energy has units of Joules (J) h = Planck’s constant = 6.626 x 10 -34 J. s E = h f

17. A photon has an energy of 1.23 x10 -16 J. What is the frequency and wavelength of the photon?

19. 1.What is the wavelength of light that has a frequency of 2.27 x10 17 hertz? 2.What is the frequency of light that has a wavelength of 680. nm? 3. What is the wavelength of light with a frequency of 4.27 x10 18 hertz? 4.A photon has an energy of 1.23 x10 -16 J. What is the frequency and wavelength of the photon?

20. 1. wavelength = 1.32 x10 -9 m 2. frequency = 3.29 x10 17 hertz 3. wavelength = 7.03 x10 -11 m 4. frequency = 1.86 x10 17 hertz wavelength = 1.62 x10 -9 m

21. So what does light have to do with chemistry? You can identify an element by the color of light it gives off when heated…

22. How is light given off? When atoms absorb energy (for example, from a flame), electrons become excited and temporarily get into a higher energy level When they drop back down to their ground state, energy is released in the form of light Atomic emission spectrum: the set of frequencies of the electromagnetic spectrum that consists of several individual lines of color corresponding to the frequencies of the radiation emitted by atoms of the element

24. Quantum Model of the Atom Bohr proposed that atoms only have certain allowable energy states The lowest allowable energy state of an electron is called its ground state Bohr assigned a quantum number, n, to each orbit (1,2,3,4,5,6,7)

25. Quantum Model of the Atom Principle Energy Levels (n) – THERE ARE 7! n = 1, 2, 3, 4, 5, 6, or 7 Specifies the electron’s energy level Within each principal energy level, the electrons occupy energy sublevels Energy sublevels: The # of energy sublevels = the principal energy level - Ex. – The 3 rd principal energy level has 3 sublevels Sublevels are labeled s,p,d,f

26. Quantum Model of the Atom Sublevels are labeled according to the SHAPE of the orbital What is an orbital? Atomic Orbital: region of space that has a high probability of finding an electron (1 orbital can hold up to 2 electrons)

27. There are four main types of orbitals: s, p, d, f The different types of orbitals refer to different types or shapes Electron orbitals

28. Heisenberg’s uncertainty principle: You can not know the exact location or speed of the electron - Whatever instrument is being used to measure the electron’s speed or direction will alter just that An “electron’s address” includes 4 quantum numbers: n, l, m, s Calculating these numbers will give information about the distribution of electrons in an atom

29. Orbital Diagrams Aufbau Principle – electrons enter orbitals of lowest energy first Pauli exclusion principle – a maximum of 2 electrons may occupy a single atomic orbital, but only if the electrons have opposite spins. Hund’s Rule – when electrons occupy orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with spins parallel

30. Orbital Diagrams – a way of putting electrons into a diagram that ranks the orbitals from lowest to highest energy 1. Fill from the lowest to highest energy level 2. The number of orbitals (lines) depends on the type of orbital- s : 1, p : 3, d : 5, f : 7 3. Electrons are shown as arrows pointing up or pointing down 4. Each orbital can hold at most 2 electrons, one pointing up and one pointing down 5. If you reach a point where 3 or more lines are at the same energy, put one arrow pointing up on each line before the second arrow is added pointing down.

31. 1s 2s 2p 3s 3p 4s 4p 3d 5s

32. Summary 1. What is an atomic orbital? 2. What is the ground state of an atom? 3. How many principal energy levels are there in an atom?

33. Summarize with a partner… How many electrons can go in a d orbital? How many sublevels are in the 4 th principle energy level? How many electrons can go in the 3 rd energy level?

34. Electron Configurations – a different way of showing the electrons distributed in the different orbitals 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 … Type of orbitalEnergy Level Number of electrons

35. Writing electron configurations using the Periodic Table Each period (row) counts as an energy level Four different sections on the periodic table: s block (group 1, 2 and He) p block (groups 13-18) d block (groups 3-12) f block (two rows at the bottom) Each box or element represents an electron d block is one energy level behind, the f block is two energy levels behind

37. Try this one… Draw the orbital diagram and write the electron configuration notation for oxygen and iron.

38. Noble Gas Configurations Noble gas configurations – a method of representing electron configurations with noble gases. (i.e. a short cut to writing electron configurations) Sodium: Complete electron configuration: 1s 2 2s 2 2p 6 3s 1 Noble gas configuration: [Ne]3s 1

39. Valence Electrons Valence electrons – electrons in the highest energy level (outermost atomic orbital) Involved in bonding Can either be lost (to form a positive ion) or gained (to form a negative ion) A full valence shell is more stable

40. Electron-dot Structure Electron – dot Structures – consists of the element’s chemical symbol surrounded by the valence electrons ONa Al