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October 10, 2016 ATOMIC STRUCTURE Table of Contents Click on the topic to go to that section • The Bohr Model The Bohr Model • Quantum Mechanics • The Quantum Model • Energy Level Diagrams and Electron Configurations Return to Table of Contents Table of Contents Bohr Model The Problem with the Nuclear Atom Democritus Dalton Thomson Rutherford We have established so far: 460 BC 1803 1897 1912 1. Atoms are made of protons, neutrons, and electrons. ? 2. Protons and neutrons make up the mass of an atom and are found together in the small, dense nucleus. 3. The electrons are found outside the nucleus and occupy the vast majority of the volume. Atomos Dalton's Plum Nuclear Postulates Pudding Model Question: What are some problems with this model? Model Evolution of Theory Atomic Model Answer Evolution of Atomic Theory Positive and negative ch attract, so why aren't electrons and protons tog Why don't the electrons " the nucleus? October 10, 2016 The Problem with the Nuclear Model The Problem with the Nuclear Model 2. Only when energized, atoms do emit energy. A continuous spectrum is not produced; instead, an emission spectrum of only specific wavelengths and frequencies is produced. This is also referred to as a line spectrum. 1. Most atoms are stable and do not release energy at all. If electrons were continuously orbiting the nucleus in uniform circular motion, like the Nuclear model predicted, they would be accelerating; accelerating charges release energy as a continuous spectrum. e External energy added (electricity, light, etc.) emits energy e e light energy emitted Emission Spectrum continuous spectrum nucleus Observations Observations 1 When atoms are energized by electricity, what is observed? 2 Why was the Nuclear Model insufficient? Answer B It could not account for the stability of the atom A A continuous spectrum of light B C It required the electrons to be in the nucleus and the protons in orbit around the nucleus D A and B B An emission spectrum of specific colors only. C Neither a nor b Question Question Answer A It could not explain the existence of emission spectra D October 10, 2016 Emission Spectra and the Bohr Model Niels Bohr interpreted these observations and created a new model of the atom that explained the existence of emission spectra and provided a framework for where the electrons can exist around the nucleus. Emission Spectra and the Bohr Model Bohr knew that the wavelengths seen in the emission spectra of hydrogen had a regular pattern. Each series was named after the scientist who observed these particular spectral lines. Lyman Series (spectral lines in the UV range) Balmer Series (spectral lines in the visible and UV range) Paschen Series (spectral lines in the infrared range) Emission Spectra Emission Spectra and the Bohr Model Bohr proposed that electrons could orbit the nucleus, like planets orbit the sun...but only in certain specific orbits. Emission Spectra Emission Spectra and the Bohr Model Each orbit would correspond to a different energy level for the electron, designated by "n" n = 3 n = Increasing energy 2 n = 1 + Emission Spectra Emission Spectra October 10, 2016 Emission Spectra and the Bohr Model The Bohr Atom The lowest energy level is called the ground state; the others are excited states. Bohr reasoned that each spectral line was being produced by an electron moving from a high energy orbit to a lower energy orbit, and giving off energy in the form of light. Hydrogen atom n = 4 n = 3 n n = 2 5 4 3 n = 1 + 2 1 Since only certain frequencies of light were produced, only certain orbits must be possible. Bohr Atom Emission Spectra Emission Spectra and the Bohr Model The energy of each orbit is quantizedonly certain values were possible. The emission spectrum could be explained as movment of electrons from a higher energy orbit to a lower energy orbit. 3 According to Bohr, "n" stands for... A the number of cycles C the energy level of the orbit D the number of orbits upper e lower Emission Spectra e upper lower Question Answer B the number of electrons C October 10, 2016 4 In the Bohr model of the atom an electron in its lowest energy state 5 Which of the following best explains why excited atoms produce emission spectra and not continuous spectra? Answer B is farthest from the nucleus C is in an excited state D emits energy A B A continuous spectrum requires the movement of neutrons C Electrons can only exist in certain stable orbitals of specific energies D Electrons can exist and move anywhere around the nucleus and are not bound to a specific orbit Question Question Emission Spectra and the Bohr Model Emission Spectra and the Bohr Model According to Bohr's model, electrons can absorb energy and move from a lower energy orbital to a higher energy orbital. An excited electron can release energy and move down to any lower energy orbital. The energy that the electron either absorbs or emits must equal the difference between the two energy levels of the orbitals involved. n = 4 n = 3 n = 2 n = 1 + Here we see 2 separate emissions coming from the same electron. The electron can either go from n=3 right to n=1 or it can go from n=3 to n=2 to n=1. n = 2 n = 2 n = 1 + Both are acceptable and both will occur. Emission Spectra n = 4 n = 3 n = 4 n = 3 photon Emission Spectra n = 1 + Answer A Not all atoms contain enough electrons to produce a continuous spectrum A is in the ground state C October 10, 2016 Emission Spectrum of Hydrogen Emission Spectra and the Bohr Model Hydrogen atoms have one proton and one electron. The emission spectrum of hydrogen shows all of the different possible wavelengths of visible light emitted when an excited electron returns to a lower energy state. Transition light emitted The difference in energy between neighboring orbits decreases as one moves farther from the nucleus. E = hν c = λν n = 3 6 2 4 2 3.03 x 1019 2 > 1 122 1.63 x 1018 Transition n = 1 486 nm + + 3 2 3 > 2 wavelength of spectral line produced (nm) 656 n = 2 410 nm Energy (J) 656 nm Click here for Bohr model animation Hydrogen Emission Spectra Emission Spectra and the Bohr Model 6 Which of the following electron transitions would produce the highest energy spectral line? The energy differences between the Bohr orbits were found to match exactly the energy of a particular spectral lines in the emission spectra of Hydrogen. n = 1 19 Energy of n = 3 = 2.417 x 10 J B 3 > 2 Energy of n = 2 = 5.445 x 1019 J n + 19 19 ∆E = (2.417 x 10 J) (5.445 x 10 J) 19 ∆E = 3.028 x 10 J C 4 > 3 5 4 3 2 D 2 > 1 Hydrogen emission spectrum 1 Red line wavelength (λ)= 656.3 nm E = hf or E = hc/λ E = 3.0 x 1019 J Emission Spectra Question Answer n = 2 A 5 > 4 Notes n = 3 D October 10, 2016 Emission Spectra and the Bohr Model Emission Spectra and the Bohr Model Due to the differing numbers electrons, atoms of each element produce a unique emission spectrum after being energized. The emission spectrums can be used to identify the presence of a particular element. Emission spectrum of Iron Emission Spectra Since electrons can only move between orbits of set energies atoms must absorb energy at the same frequencies at which they emit energy. As a result, monitoring which frequencies of light are absorbed can help us determine which element or molecule is present. Absorption Emission Spectra 7 The emission spectrum for Chlorine is shown below. Which of the following represents Chlorine's corresponding absorption spectrum? A B Answer Absorption vs. Emission Answer Below are the visible wavelength emission spectra for hydrogen and iron. What difference do you notice about the two spectra? Propose a reason for this difference. Emission spectrum of Hydrogen C Question October 10, 2016 9 Which of the following is NOT true regarding the Bohr model of the atom? Does the picture below illustrate a photon emission or absorption? n = 4 n = 3 B n = 2 Emission A Electrons could exist only in certain quantized orbits around the atom n = 1 Absorbtion + C Neither D Both B As "n" becomes greater, the energy of the orbit is greater also C When returning from an excited state, an electron can can only move between the set Bohr orbits D All of these are true Question Question Rutherford vs Bohr Model Quantum Mechanics The Bohr model could only explain the emission spectrum of hydrogen with one electron. It could not adequately the behavior of atoms with more than one electron. Return to Table of Contents Aug 99:05 PM Quantum Mechanics Answer A Answer 8 D October 10, 2016 THE PROBLEM WITH THE BOHR MODEL Bohr’s model could only describe the behavior of a hydrogen atom, which only has one electron. The Bohr model could not explain the emission spectra of atoms with more than one electron. Scientists needed to find a new way to explain how electrons are arranged around the nucleus. Bohr model of a hydrogen atom QUANTUM MECHANICS Quantum mechanics was a major breakthrough that helped scientists better understand the atom in a way that classical physics could not do. Scientists first tried to use classical physics to explain how electrons are arranged—but it could not explain the behavior of subatomic particles like electrons. Feb 224:27 PM THE QUANTUM MECHANICAL MODEL Erwin Schrödinger helped improve our understanding of the atomic model. He combined the following concepts: (1) First, electrons are particles, but they also act like waves (remember de Broglie proposed that matter can act like a wave). Feb 224:28 PM 10 It is possible to know the exact path of an electron. True False (2) Second, scientists could not accurately predict where a particle, like the electron, is and its momentum at the same time—this is referred to as the Heisenberg uncertainty principle. Scientists could only determine the probability of an electron being in a certain area around the nucleus. Answer The Schrödinger Wave Equation. This equation is used to determine the probability of finding an electron in a certain area around the nucleus. Feb 224:28 PM Question False October 10, 2016 uncertainty principle. C photoelectric effect. D principle of relativity. Answer B Question C remain the same. D be uncertain. Question remain the same. D be uncertain. THE QUANTUM MECHANICAL MODEL The quantum mechanical model of an atom treats the electron as both a wave and a particle. Instead of predicting definite paths the electron travels in—like the Bohr model— the quantum mechanical model predicts the probable location of finding an electron. Answer decrease. decrease. C Question 13 If the accuracy in measuring the momentum of a particle increases, the accuracy in measuring its position will A increase. B B B Feb 224:28 PM Answer 12 If the accuracy in measuring the position of a particle increases, the accuracy in measuring its momentum will A increase. 11 The idea that the position and momentum of an electron cannot measured with infinite precision is referred to as the A exclusion principle. October 10, 2016 Bohr Model vs Quantum Mechanical QUANTUM NUMBERS Quantum numbers (n, l, ml, ms) are used to describe the probable location of finding an electron in an orbital . NOTE: No two electrons in an atom may have the same set of quantum numbers. n = the energy level of the orbital; the energy level is also referred to as a shell l = the shape of the orbital, (s,p,d,f) ml = the orientation of the orbital in space ms = the direction of the electron spin How many quantum numbers are used to describe the probable location of an individual electron? Feb 224:32 PM Aug 99:05 PM 15 Quantum mechanics allows to you predict exactly what an electron will due. 14 Quantum mechanics provides a mathematical definition for the: A wavelike properties of electrons only. B particlelike properties of electrons only True Question Answer D the waveparticle duality of electrons Answer False C classic Newtonian forces that govern atoms D Question False October 10, 2016 QuantumMechanical Model of the Atom Since we can't say exactly where an electron is, the Bohr model, with electrons in neat orbits, can't be correct. Quantum theory describes an electron probability distribution; this figure shows the distribution for the ground state of hydrogen. The Quantum Model In this picture, the probability of finding an electron somewhere is represented by the density of dots at that location. Return to Table of Contents The Quantum Model Quantum View of Atoms Quantum Numbers Solutions to Schrodinger's Wave Equation take the form of sets of numbers. There are four different quantum numbers: n, l, ml, ms needed to specify the state or probable location of an electron in an atom. n = principal l = angular ml = magnetic ms = spin n = 4 Orbitals An orbital is a region of space where an electron is most likely to be found. Note: A maximum of two electrons can be found in each orbital. Y n = 3 n = 2 n = 1 + X Z energy level/ distance from nucleus shape of orbital orientation of orbital in space Quantum Numbers + direction of electron spin Aug 99:52 PM October 10, 2016 (n): Principal Quantum Number 16 The principal quantum number, n, determines the ____________ of the orbital. n = 4 The principal quantum number, n, describes the energy level of the orbital, often called the energy shell. The values of n are integers greater than or equal to 1: n ≥ 1 n = 3 n = 2 n = 1 A Orientation B Energy C Shape D Capacity + Answer In general, the larger the value of n, the farther from the nucleus the electron should be found. Principal Quantum Number Question 17 As n increases, the orbital energy _________ . Each orbital region has a very specific shape based on the energy of the electrons occupying them and a specific orientation in space. Increases B Decreases (l): Angular Quantum Number C Remains constant Quantum number l designates the shape of the orbital. D Increases then decreases Answer A There are four shapes of orbitals: s,p,d,f (ml): Magnetic Quantum Number Quantum number ml designates the orientation of the orbital in space. Question Angular & Magnetic Numbers October 10, 2016 Electron Orbital Shape and Orientations The s orbital s orbitals are spherical in shape.The radius of the sphere increases with the value of n. If you are looking for an electron in an s orbital, the direction you look in doesn't really matter, they have only one orientation in space. 1 1 2 2 If l = s shape ml = 1 orientation 1 orbital per energy level http://chemwiki.ucdavis.edu/@api/deki/files/4826/=Single_electron_orbitals.jpg Orbital Shape s Subshell The p orbital p orbitals have two lobes with a node between them. The p orbitals come in a set of three, each at a different orientation in space. l = p shape ml = 3 orientations 3 orbitals per energy level p Subshell The d orbital High probability of finding an electron d orbitals have more complex shapes. There are 5 possible orientations in space, so there are 5 possible d orbitals. Low probability of finding an electron l = d shape ml = 5 orientations 5 orbitals per energy level d Subshell 3 3 October 10, 2016 The f orbital There are 7 possible f orbitals. # of orbitals # of electrons s p d f l = f shape ml = 7 orientations 7 orbitals per energy level f Subshell Aug 1212:31 PM 19 The magnetic quantum number, m , determines 18 The quantum number, l, determines the ____________ of the orbital. B Energy C Shape D Capacity Question A Orientation B Energy C Shape D Capacity Answer Orientation Answer A l the ____________ of the orbital. Question October 10, 2016 20 A(n) ___ orbital is lobeshaped 21 An s orbital has ______ possible orientations in s A 1 B p B 3 C d C 5 D f D 7 Answer A Question Answer space. Question Spin Quantum Number, m 22 An f orbital has ______ possible orientations in s A 1 B 3 C 5 D 7 Answer space. The spin quantum number can be positive or negative. This implies that electrons are in some way able to pair up, even though they repel each other due to the electromagnetic force. Each orbital can therefore hold maximum of 2 electrons that must spin in the opposite directions. spin Question Spin Number + spin A October 10, 2016 can only have two values A the same spin B relates to the spin of the electron B no spin C relates to the spin of the atom C opposite spins D Both A & B D electrons cannot occupy the same orbital Answer A Question Question Energy Levels and Sublevels Quantum Numbers Subshells Some combinations of Quantum Numbers are impossible: For example, you don't find p, d, or f orbital in the first energy level. Orbitals with the same value of n form a shell. Different orbital types within a shell are subshells. n subshell # of orbitals total # total # of orbitals of electrons 1 1s 1 1 2 2 2s 1 2p 3 4 8 3 3s 1 3p 3 3d 5 9 18 4 4s 1 4p 3 4d 5 4f 7 16 32 Energy Levels & Sublevels Quantum Number Subshells Answer 24 Electrons within the same orbital must have 23 The spin quantum number, ms October 10, 2016 25 If n = 1 an electron can occupy which of the subshells? A 1s 2p D 3s A Answer C 2 Answer 2s Answer B 26 n = 1 can hold a maximum of ___ electrons 6 Click here for an electron orbital game. Question Question 27 What is the maximum number of electrons 28 An electron is in the 6f state. Determine the principal quantum number. Answer that can occupy the n = 4 shell? Question 32 Question October 10, 2016 29 An electron is in the 6d state. How many Energies of Orbitals electrons are allowed in this state? 10 For example: the energy of 4s is less than the energy of 3d. 7d 6f 7 6 7p 6d 5f 7s 6p 5d Energy Answer 7f Notice that some sublevels on a given n level may have less energy than sublevels on a lower n level. 5 6s 5p 4 5s 3 4s 2 3s 1 2s 4f 4d 4p 3d 3p 2p 1s Question Feb 310:30 AM Energy Level Diagram / Orbital Diagrams Orbital diagrams are a way to illustrate the energy levels of electrons. Each box in the diagram represents one orbital. Energy Level Diagrams & Electron Configurations Arrows represent the electrons. The direction of the arrow represents the relative spin of the electron (+ or ). 8 Return to Table of Contents Electron Configurations O 1s 2s 2p Orbital Diagrams October 10, 2016 Energies of Orbitals Electron Orbital Diagram 30 In an electron orbital diagram, an individual box represents? A Energy level Orbital diagrams can also be drawn vertically to illustrate increasing energy. B Orbital C The electron To complete an orbital diagram you must first know how many electrons the atom has. D The electron spin In a neutral atom: # of electrons = # of protons so the # of electrons will be the same as the atomic number. 6 C Energies of Orbitals 31 In an electron orbital diagram, which symbol represents an electron? A B Question 32 In an electron orbital diagram, the three orbitals together indicate each orbital occupies A The same energy level B The same electrons C C Different energy levels D both B and C D Different electron spins Question Question October 10, 2016 3 Rules for Filling Electron Orbitals Aufbau Principle Aufbau Principle Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atoms have been accounted for. Aufbau takes its name from a German word meaning "building up". Pauli Exclusion Principle Electrons fill the lowest energy orbitals first. An orbital can hold a maximum of two electrons. To occupy the same orbital, two electrons must spin in the opposite direction. Hund's Rule One electron is placed in each of the equal energy orbitals (set of 3 p's, set of 5 d's, etc) before a second electron is added. 3 Rules Aufbau Hund’s Rule Pauli Exclusion Principle Two electrons in the same orbital must have opposite spins. The up arrow is always written first. correct 1s2 2s2 Every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin. incorrect correct 2p1 1s2 2s2 2p2 1s2 2s2 2p2 incorrect Think about the Empty Bus Seat Rule. People will not sit next to each other on a bus until all the seats are taken up 1s2 2s2 2p1 Pauli Exclusion Hunds October 10, 2016 Answer Fill in the Energy Level Diagram for Magnesium, Mg. Fill in the Energy Level Diagram for Chlorine, Cl. Practice Practice Energy Level Diagram 33 The orbital diagram below depicts electrons in which element? Fill in the Energy Level Diagram for Iron, Fe. Answer A Oxygen B Sodium C Aluminum D Iron Practice Question Answer Energy Level Diagram Energy Level Diagram October 10, 2016 34 The orbital diagram below depicts electrons in which element? A Boron B Carbon 35 What is wrong with the electron orbital diagram below? A Electrons are not filling lower energy orbitals first violation of the Aufbau Principle. B Two electrons occupying the same orbital have the same spin violation of the Pauli Exclusion Principle. C Nitrogen D Neon C Some orbitals are double occupied by electrons before every orbital has at least one electron violation of Hund's Rule. D This orbital diagram is correct. Question Question 36 What is wrong with the electron orbital diagram below? 37 What is wrong with the electron orbital diagram below? A Electrons are not filling lower energy orbitals first violation of the Aufbau Principle. A Electrons are not filling lower energy orbitals first violation of the Aufbau Principle. B Two electrons occupying the same orbital have the same spin violation of the Pauli Exclusion Principle. B Two electrons occupying the same orbital have the same spin violation of the Pauli Exclusion Principle. C Some orbitals are double occupied by electrons before every orbital has at least one electron violation of Hund's Rule. C Some orbitals are double occupied by electrons before every orbital has at least one electron violation of Hund's Rule. D This orbital diagram is correct. D This orbital diagram is correct. Question Question October 10, 2016 38 What is wrong with the electron orbital diagram below? 39 What is wrong with the electron orbital diagram below? A Electrons are not filling lower energy orbitals first violation of the Aufbau Principle. A Electrons are not filling lower energy orbitals first violation of the Aufbau Principle. B Two electrons occupying the same orbital have the same spin violation of the Pauli Exclusion Principle. B Two electrons occupying the same orbital have the same spin violation of the Pauli Exclusion Principle. C Some orbitals are double occupied by electrons before every orbital has at least one electron violation of Hund's Rule. C Some orbitals are double occupied by electrons before every orbital has at least one electron violation of Hund's Rule. D This orbital diagram is correct. D This orbital diagram is correct. Question Electron Configurations Question Electron Configurations Electron configurations show the distribution of all electrons in an atom. Electron configurations show the distribution of all electrons in an atom. Each component consists of: Each component consists of: A number denoting the shell A number denoting the shell, A letter denoting the type of subshell Electron Configurations Electron Configurations October 10, 2016 Electron Configuration of Sodium Electron Configurations For example, the groundstate configuration of sodium is: Electron configurations show the distribution of all electrons in an atom. Each component consists of: 2 1s2 2s 2p6 3s1 Slide • A number denoting the shell, • A letter denoting the type of subshell, and • A superscript denoting the number of electrons in those orbitals. Check Your Work: All of the superscript numbers add up to the total number of electrons. 23 11 Na Sodium Atom Remember in a neutral atom the # of electrons = # of protons Electron Configurations Electron Configuration of Na Practice Practice Write the Ground State Electron Configuration for Phosphorous, P. Electron Configuration Write the Ground State Electron Configuration for Calcium, Ca. Practice Answer Answer Electron Configuration 1s22s22p63s23p3 Practice 1s22s22p63s October 10, 2016 Practice Practice Write the Ground State Electron Configuration for Titanium, Ti. Write the Ground State Electron Configuration for Bromine, Br. 1s22s22p63s23p64s23d2 Answer Answer Electron Configuration Practice Practice 40 What is the electron configuration for Li ? A 1s3 B 1s1 2s2 D 1s2 1p1 B 1s22s23s23p6 Question C 1s22s22p6 D 1s22s22p63s23p64s1 Question Answer 1s2 2s1 A 1s22s23s23p64s2 Answer C 41 Which of the following is the correct electron configuration for Potassium (K)? 1s22s22p63s23p64 October 10, 2016 42 A neutral atom has an electron configuration of 1s 2s 2p 3s 3p1. What is its atomic number? A 5 B 11 C 13 D 20 6 43 A neutral atom has the following electron configuration: 1s2 2s2 2p6 3s2 3p64s23d104p3. What element is this? 2 A zinz B copper C arsenic D germanium Question C D 1s22s32p6 none of the given answers Question Question * Energy Level Diagram Excited State Answer 44 A neutral atom has an electron configuration of 1s2 2s2 2p6 . If a neutral atom gains one additional electron, what is the ground state configuration? A 1s22s22p63s1 B 1s22s22p7 Answer 2 Answer 2 In a sodiumvapor lamp electrons in sodium atoms are excited to the 3p level by an electrical discharge and emit yellow light as they return to the ground state. Excited State Na Excited State Energy Level Diagram October 10, 2016 * * 46 Which of the following represents an excited state electron configuration for Magnesium (Mg)? 1s22s22p63s1 A 1s22s22p63s2 B 1s22s22p7 B 1s22s22p73s1 C 1s22s22p63p1 C 1s22s22p63s13p1 D none of the given answers D none of the above Answer A Question Question Paired and Unpaired Electrons When two electrons occupy the same orbital, they are called paired electrons. When a single electron is by itself, it is an unpaired electron. EXAMPLE: 1s22s22p63s23p1 Aluminum has one unpaired electron. Sep 64:35 PM Answer 45 Which of the following represents an excited state electron configuration for Sodium (Na)? Attachments =Single_electron_orbitals.webloc