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Chapter 5: Electrons in Atoms REVISING THE ATOMIC MODEL ELECTRON ARRANGEMENT IN ATOMS ATOMIC EMISSION SPECTRA AND THE QUANTUM MECHANICAL MODEL Learning Targets You will: 1. Determine the energy levels, sublevels and orbitals of electrons in an atom. 2. Determine how to write electron configuration and orbital notation for atoms and ions. Atom Models … Rutherford: couldn’t explain chemical properties of elements Bohr: explained how energy levels of electrons in an atom change when the atom emits light Schrodinger: devised and solved mathematical equation describing electron behavior in atom Restricts energy of electrons to certain values Doesn’t specify exact path electron takes around nucleus Calculations show previous models didn’t always correctly describe electron motion You will determine the energy levels, sublevels and orbitals of electrons in an atom. Quantum Mechanical Model Probability of finding an electron represented as fuzzy, cloudlike region Cloud more dense when probability high Atomic orbital is pictorially a region of space where high probability of finding electron You will determine the energy levels, sublevels and orbitals of electrons in an atom. Quantum Mechanical Model Energy levels labeled by principal quantum numbers (n) and assigned values of 1, 2, 3, 4 and so on Energy levels within principal energy level are sublevels Each sublevel corresponds to one or more orbitals of different shapes You will determine the energy levels, sublevels and orbitals of electrons in an atom. Summary of energy levels and sublevels You will determine the energy levels, sublevels and orbitals of electrons in an atom. Atomic Orbitals Principal quantum number, n, = # sublevels w/in principal energy level # orbitals in principal energy level = n2 Maximum of 2 electrons can occupy an orbital Maximum number of electrons that can occupy an energy level = 2n2 Example: Calculate the maximum number of electrons in the 5th principal energy level (n = 5). The maximum number of electrons that can occupy a principal energy level is given by the formula 2n2. If n = 5, 2n2 = 50. You will determine the energy levels, sublevels and orbitals of electrons in an atom. Sublevels and Energy Levels You will determine the energy levels, sublevels and orbitals of electrons in an atom. Table talk … What causes atomic emission spectra? When atoms absorb energy, their electrons move to higher energy levels. These electrons lose energy by emitting light when they return to lower energy levels. No two elements have the same emission spectrum. You will determine the energy levels, sublevels and orbitals of electrons in an atom. You will determine the energy levels, sublevels and orbitals of electrons in an atom. What we saw in the lab … Nature of light c = ln Amplitude = wave’s height from zero to crest Wavelength = distance b/t crests Frequency = # wave cycles to pass given point/unit of time Frequency and wavelength inversely proportional Product of frequency and wavelength = constant (c), speed of light Nature of Light Electromagnetic radiation includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, x-rays and gamma rays All waves travel at a speed of 3.00 x 108 m/s Example Calculate the wavelength of the yellow light emitted by a sodium lamp if the frequency of the radiation is 5.09 × 1014 Hz (5.09 × 1014/s). c =ln 𝑐 =l 𝑣 3.00 x 10^8 m/s 5.09 x 10^14 Hz 5.89 =l x 10-7 m = l Try on your own What is the frequency of a red laser that has a wavelength of 676 nm? c=ln 𝑐 l =n 1m 676 nm 1 x 10^9 nm 3.00 x 10^8 m/s =n 6.76 x 10^−7 m 4.44 x 1014 Hz = n = 6.76 x 10-7 m Quantum Concept and photons German physicist Max Planck showed mathematically that the amount of energy (E) absorbed or emitted is proportional to the frequency of radiation (n). The constant (h) has a value of 6.626 x 10-34 Js and is called Planck’s constant Example What is the energy of a photon of microwave radiation with a frequency of 3.20 × 1011/s? E =hn E = 6.626 x 10-34 Js 3.20 x 1011/s E = 2.12 x 10-22 J Try on your own What is the frequency of a photon whose energy is 1.166 x 10–17 J? E =hn 𝐸 =n ℎ 1.166 x 10^−17 J 6.626 x 10^−34 Js 1.760 =n x 1016 Hz = n Table talk … What are the three rules for writing the electron configurations of elements? Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms. Aufbau principle: electrons occupy orbitals of lowest energy first before filling higher energy levels Pauli exclusion principle: two electrons must have opposite spins to occupy the same orbital Spin is a quantum mechanical property of electrons A vertical arrow indicates an electron and its direction of spin Hund’s rule: every orbital is singly occupied with one electron before any orbital is doubly occupied, all electrons in singly occupied orbitals have the same spin. You will determine how to write electron configuration and orbital notation for atoms and ions. Electron Configurations Convenient shorthand method involves writing energy level and symbol for every sublevel, then indicate the number of electrons w/superscript Sum of the superscripts = # electrons in atom You will determine how to write electron configuration and orbital notation for atoms and ions. Electron Configurations You will determine how to write electron configuration and orbital notation for atoms and ions. Examples Write the electron configuration for the following atoms: Answers: 1. 1s1 1. hydrogen 2. 1s2 2s2 2p3 2. nitrogen 3. aluminum 3. 1s2 2s2 2p6 3s2 3p1 You will determine how to write electron configuration and orbital notation for atoms and ions. Electron Configurations You will determine how to write electron configuration and orbital notation for atoms and ions. More Examples Write the electron configuration for the following atoms: Answers: 1. 1s2 1. helium 2. 1s2 2s2 2p4 2. oxygen 3. silicon 3. 1s2 2s2 2p6 3s2 3p2 You will determine how to write electron configuration and orbital notation for atoms and ions. Electron Configurations You will determine how to write electron configuration and orbital notation for atoms and ions. Try on your own Write the electron configuration for the following atoms: 1. sodium 2. phosphorus 3. potassium Answers: 1.1s2 2s2 2p6 3s1 2.1s2 2s2 2p6 3s2 3p3 2 2 6 2 6 1 3.1s 2s 2p 3s 3p 4s You will determine how to write electron configuration and orbital notation for atoms and ions. Electron Configurations You will determine how to write electron configuration and orbital notation for atoms and ions. Orbital Notation Orbital notation is a way of drawing electron configurations A box or blank indicates the space for an orbital Remember an orbital can hold two electrons An orbital will correspond to each energy level and sublevel in the configuration You will determine how to write electron configuration and orbital notation for atoms and ions. Examples Write the orbital notation for the following atoms: 1. Sulfur 2. Silicon 3. Magnesium You will determine how to write electron configuration and orbital notation for atoms and ions. Electron Configurations Electron Configuration and Orbital Notation change for elements after the first 20. This is because instead of going in order of each energy level and sublevel, we jump from the 4s to 3d An example of an electron configuration with this: Se 1s22s22p63s23p64s23d104p4 Notice the jump from 4s to 3d then back to 4p You will determine how to write electron configuration and orbital notation for atoms and ions. Examples Give the electron configuration for gallium (Ga), bromine (Br) and hafnium (Hf). Ga – 1s22s22p63s23p64s23d104p1 Br - 1s22s22p63s23p64s23d104p5 Hf - 1s22s22p63s23p64s23d104p65s24d105p66s24f145d2 You will determine how to write electron configuration and orbital notation for atoms and ions. Try on your own Give the electron configurations for the following elements: 1. tin (Sn) 2. lead (Pb) 3. polonium (Po) 4. iodine (I) tin (Sn) pollonium (Po) – 1s22s22p63s23p64s23d104p65s24d105p2 1s22s22p63s23p64s23d104p65s24d105p66s24 lead (Pb) f145d106p4 1s22s22p63s23p64s23d104p65s24d105p66s24 iodine (I) f145d106p2 1s22s22p63s23p64s23d104p65s24d105p5 You will determine how to write electron configuration and orbital notation for atoms and ions. Orbital Notation Pick one atom from the last set of problems and write its orbital notation You will determine how to write electron configuration and orbital notation for atoms and ions. Summarize how you feel … You will: 1. Determine the energy levels, sublevels and orbitals of electrons in an atom. 2. Determine how to write electron configuration and orbital notation for atoms and ions.