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Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Chapter 4 problem set: Page 124 Chapter Review: 8, 9, 16, 17, 18, 20, 22, 27, 28, 30, 33, 36, 37 4.1 Refinements of the atomic model Models of the atom so far: Dalton – atoms are like little “bb’s” - then the Thomson – atom is like a “bb” Rutherford - Gold foil experiment – - gets discovered “bb” 1909 - Gold Foil Experiment (Rutherford - New Zealand) - The Experiment: towards a thin sheet of seen on the particles from (in the lead box) were released foil. Most of the particles went through and were screen. alpha particles bounced back. - Concluded: 1 – 2– 3– 4– - Analogy: if an atom is the size of the Eagle’s stadium, then the nucleus is the size of a tennis ball floating in the middle of the stadium. 874009123 Page 1 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Bohr model of the atom (1913) – Neils Bohr – Danish Physicist The Bohr model of the atom comes from the idea that light is View vision learning example of hydrogen and helium atoms. http://web.visionlearning.com/custom/chemistry/animations/CHE1.2-anatoms.shtml The Bohr Atom (1913) In 1913, Neils Bohr, a Danish physicist proposed: All the positive charge was in the Electrons orbited the nucleus much like planets orbit the sun (at distances) The the electrons to the nucleus, the energy it has. The the electron is from the nucleus, the energy it has. 874009123 Page 2 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms The Electromagnetic Spectrum - Defined Visible light, x-rays, ultraviolet radiation, infrared radiation, microwaves and radio waves are all part of the electromagnetic spectrum The spectrum consists of electromagnetic radiation – Waves can be described by the wave equation which includes velocity (c = speed of ), (λ) and (ν). Wavelength (definition) = Light through prism leads to high energy (violet) low energy (red) 874009123 Page 3 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms ROYGBIV - colors of the bright line spectrum (bls) - frequencies of light give off by certain substances when is added to them. heat sodium - yellow light heat lithium - red light elements can appear to give off the same color light, but each will have its own bls - used to determine bls - validates Bohr’s idea that electrons levels and give off different wavelengths of 874009123 spectrum to different energy Page 4 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Light from the sun (white light) appears as a of light. spectrum Continuous Spectrum of Light (definition) = There are discrete, individual wavelengths of light but rather wavelengths appear, one after the other in a continuous fashion Spectroscopy (definition) = _ . Show overhead #6 We will use spectroscopes ( ) and tests to study elements because each element emits a different spectrum of light when exited . Bohr proposed that the energy possessed by an e- in a H-atom and the radius of the orbit are (bls) Quantized (definition): a specific value (of energy) The ramp is an example of a continuous situation in which any energy state is possible up the ramp 874009123 Like a set of stairs, the energy states of an electron is quantized – i.e. electrons are only found on a specific step Page 5 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Bohr’s Energy Absorption Process: Light or energy excites an e- from a lower energy level (e- shell) to a ___________energy level These energy levels are “ “ (the e- cannot be in between levels), the e- disappears from one shell and reappears in another This absorption or excitation process is called a or _________________ Ground State Analogy = a spring and two balls Both the atom and e- now have higher energy The e- absorbs energy in the ground state and is excited to a higher level “The Ground State” This is an energy emission process and what we observe in the hydrogen line spectrum “The Excited State” State” When energy is added, the electron is found in the “ The Excited State (definition) = .” _________________ 874009123 Page 6 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms An illustration of Bohr’s Hydrogen atom (from ground to excited state): The atomic line spectral lines - when an e- in an excited state decays back to the state The electron loses energy, light (colors) is emitted and the ereturns to the ground state 874009123 Page 7 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms The Bohr Model - Summary 1. When an atom absorbs , its electrons are to a higher energy level. When the electron _________, energy is given off in the form of . 2. Each distance fallen back is a specific ________, and therefore, a specific . 3. Since electrons can fall from level 5 to 4, 5 to 3, etc., . Click for animated H-atom: Bohr's Atom: Quantum Behavior in Hydrogen http://www.visionlearning.com/library/module _viewer.php?mid=51&l=15 874009123 Page 8 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Bohr also predicted that since electrons would occupy specific energy levels and each level holds a specific number of electrons The maximum capacity of the first (or innermost) electron shell is Any element with more than two e-, the extra e- reside in additional _________________. Group IA VIA VIIA VIIIA Lithium Oxygen Fluorine Neon Sodium Electron Configurations for Selected Elements The number of e- per shell = Animated Example, Atomic structure animation table - (where n is then number) http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-anatoms.shtml 874009123 Page 9 of 22 . Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Draw Bohr Models for the elements with atomic numbers 1-10 below H He Li Be B C N O F Ne 874009123 Page 10 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Bohr Model illustrations for elements 1-20 on the periodic table examples: IA VIIIA H He IIA IIIA IVA VA VIA VIIA Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca So, there is a relationship between the main column # and the number of outershell electrons. Column # = the number of electrons And, there is a relationship between the row # and the number of energy . Row # = the number of The Bohr model truly works well for the H atom only – for elements larger than H the model does not work. 874009123 Page 11 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms In sum, Bohr made 2 modern atom theory contributions to the development of He explained the atomic line spectra in terms of He introduced the idea of quantized electron in the atom The Bohr atom lasted for about 13 years and was quickly replaced by the model of the atom. The Bohr model is a good starting point for understanding the quantum mechanical model of the atom Do Ch4 worksheet #1 – question #1 4.2 Quantum numbers and atomic orbitals & 4.3 Electron Configuration The Bohr model describes the atom as having definite orbitals occupied by ___________________________. As with all chemistry, we soon learn that the Bohr model is not correct. 874009123 Page 12 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Schrödinger (1926) introduced wave mechanics to describe electrons Based his idea that electrons behaved like Electrons show diffraction ( . Treats electrons as waves that are found in o ) properties like . Charge Cloud Model In the 1930’s - 1940’s more work leads to the charge cloud model which is also known as the quantum mechanical model. This model does not show the path of - just the most location. Orbitals (definition) = . Orbitals are like "rooms" within which electrons "reside". The s subshell has ___ s-orbital. The p subshell has ____ p-orbitals. Each orbital can hold at most electrons See a good online illustration at http://www.avogadro.co.uk/light/aufbau/aufbau.htm So, the Bohr model really is the 874009123 Page 13 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms There are many types of orbitals – we can see them on the periodic table Sublevel # of orbitals e- per orbital Max # of e- per sublevel Shape of orbital s p d 5 dxy, dyz, dxz, dx2 – y2, dz2 f 7 (too complicated) 874009123 Page 14 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms - energy levels, sublevels, and total number of electrons per shell Energy Level (shell) Sublevel(s) and Electrons Total # of Electrons per Shell 1 2 3 4 5 6 7 Show transparency of orbitals in each energy level 874009123 Page 15 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Bohr Model Examples (1 to 20): H Li N K He Be B C N O F Ne Mg Al Si P S Cl Ar Ca EC for higher atomic #’s At atomic # 19 (z = 19), a break in the pattern ensues. One would expect that the orbital to fill after 3p would be 3 d, but alas, it is not. 4s is the next level we fill as it has lower energy than 3d. Look at potassium and calcium. Do Construction of Periodic Table Activity 874009123 Page 16 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Electron configurations - Electrons enter orbitals in a pattern. For the most part, they follow these rules: Aufbau principle - electrons must fill energy levels before entering higher level. examples (do Bohr models and electron configurations): Element Bohr Model Electron Configuration Oxygen Potassium Copper Silver 874009123 Page 17 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Draw diagonal diagram here: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f14 6s2 6p6 6d10 7s2 7p6 - Kernal Electrons: shell electrons - Valence Electrons: shell electrons Pauli Exclusion principle - electrons occupying the same orbital must have spin. electron spin - clockwise or counterclockwise Pauli exclusion principle - 2 electrons in the same orbital must have Hund’s rule ( better known as the Stinky Bus Rule) - before any second electron can be placed in a sub level, all the orbitals of that sub level must contain at least electron. Orbital notation is another way to represent 874009123 arrangement in atoms. Page 18 of 22 spins. Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Examples: Bohr Model, Electron Configuration, and Orbital Notation: Element Bohr Model Electron Configuration Orbital Notation Argon 1s 2s 2p 3s 3p 1s 2s 2p 3s 3p Manganese 4s 3d - example Iodine (Bohr model, electron configuration, orbits, and orbital notation: 5p 874009123 Page 19 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms - Exceptions to the Aufbau Principle - Cr is ________________ not 4s2 3d4 - Other exceptions: - students should be able to identify these elements simply based on how many electrons they have. Do the orbital notation for Copper: Significance of electron configurations 874009123 - Valence shell electrons - - for n = 5, pattern is very complicated valence electrons - Noble gases - - kernel - part of the atom the nucleus) - example - sodium kernel = valence electrons - electrons involved with bonding no atom has more than reactive of all elements of valence electrons (includes Page 20 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms - Element examples (find the outershell electron configuration, shorthand notation, and Lewis dot diagram – Outershell Electron Configuration Shorthand Notation Lewis Dot Diagram Oxygen Chlorine Iron Cobalt Potassium Strontium Silver K+1 O-2 874009123 Page 21 of 22 Accelerated Chemistry Chapter 4 Notes – Arrangement of Electrons in Atoms Quantum numbers show the “addresses” of electrons – each electron has 4 different quantum numbers: 1. principle (n): 2. azimuthal (l): 3. magnetic – 4. spin - 874009123 Page 22 of 22