Chem What is the difference between an orbit (Bohr model) and an orbital (quantum mechanical model)?

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1 Reading: sections As you read this material, ask yourself the following questions: What are wave functions and orbitals, how do orbitals differ from orbits? What can we learn about an electron from a wave function? What properties of the electron do the principal quantum number, the angular momentum quantum number and the magnetic quantum number determine. What values can each of these quantum numbers have, how are their values related? What are the shapes of the orbitals for different values of the angular momentum quantum number (different subshells)? Sketch these shapes. What labels do we give these subshells? How do the energy levels differ in many electron atoms? What is the fourth quantum number and what values can it have? When assigning energies to electrons, what are the implications of the Pauli Exclusion principle? Chem What is the difference between an orbit (Bohr model) and an orbital (quantum mechanical model)? A. An orbital is composed of some integral number of orbits. B. An orbit is a well-defined circular path around the nucleus while an orbital is a wave function that gives the probability of finding the electron at any point in space. C. An orbit is a well-defined circular path around the nucleus while an orbital is the object (electron) that is moving around the nucleus. D. There is no difference between the definitions of the terms orbit and orbital. They simply were proposed by different scientists. E. AL. 1

2 What is the difference between an orbit (Bohr model) and an orbital (quantum mechanical model)? B. An orbit is a well-defined circular path around the nucleus while an orbital is a wave function that gives the probability of finding the electron at any point in space. How many maxima would you expect to find in the radial probability function for the 4s orbital of the hydrogen atom? How many nodes would you expect in the 4s radial probability function? A. three maxima and three nodes B. three maxima and four nodes C. four maxima and three nodes D. four maxima and four nodes E. OK; so the 1s orbital has one maximum (at the nucleus) and no nodes (we don t count the one at infinity). So the 2s orbital must be different. Is it the same shape? let s check my notes yes, spherical. Does it have a node? One? That would make it different, I suppose. Where is it? Somewhere between the nucleus and infinity, I guess, but where? The suspense is killing me maybe it doesn t matter. All right then, let s put it at an arbitrary distance x from the nucleus. If there is a node there must be at least two maxima. So far so good. Moving on to the 3s orbital again, same shape, but somehow different, I m guessing another node so if it 2

3 How many maxima would you expect to find in the radial probability function for the 4s orbital of the hydrogen atom? How many nodes would you expect in the 4s radial probability function? C. four maxima and three nodes node = probability of finding an electron is 0 For an s orbital the number of nodes is given by n 1 What is not possible? (Once you ve solved that pass the time by sketching and naming the others) A. n=2, l=1,m=-1 B. n=3, l=2,m=0 C. n=3, l=1,m=2 D. n=4, l=0,m=0 E. n=1, l=0,m=0 3

4 What is not possible? (Once you ve solved that pass the time by sketching and naming the others) A. n=2, l=1,m=-1 2p x(or y or z) B. n=3, l=2,m=0 3d xy (or xz or yz or z2 or x2-y2) C. n=3, l=1,m=2 D. n=4, l=0,m=0 4s E. n=1, l=0,m=0 1s What is not possible? (n, l, m l ) (Once you ve solved that pass the time by sketching and naming the others) A. 3,2,1 B. 1,0,0 C. 2,1,2 D. 4,3,-3 E. 5,0,0 4

5 What is not possible? (n, l, m l ) (Once you ve solved that pass the time by sketching and naming the others) A. 3,2,1 B. 1,0,0 C. 2,1,2 D. 4,3,-3 E. 5,0,0 3d (any of xy, yz, xz, z 2, or x 2 -y 2 ) 1s Not possible 4f (let s not discuss the m l values) 5s What is the allowed set of quantum numbers? (n, l, m l ) (Once you ve solved that pass the time by sketching it) A. 1,1,0 B. 2,3,1 C. 3,1,2 D. 3,1,1 E. 2,1,-2 5

6 What is the allowed set of quantum numbers? (n, l, m l ) (Once you ve solved that pass the time by sketching it) A. 1,1,0 B. 2,3,1 C. 3,1,2 D. 3,1,1 E. 2,1,-2 3p (can be x,y or z) y is drawn What does the change in colour of the orbital represent in the picture below? A. The variations in pink color do not represent any significant physical feature. B. The lighter pink regions represent more positively charged areas of the p-orbital. C. The probability of finding an electron in the interior of a p-orbital lobe is less than it is on the edges. D. The probability of finding an electron in the interior of a p-orbital lobe is greater than it is on the edges. E. Artistic license. 6

7 What does the change in colour of the orbital represent in the picture below? B. The probability of finding an electron in the interior of a p-orbital lobe is greater than it is on the edges. Based on the structure of the periodic table, which orbital becomes occupied first? A. the 5d orbital B. the 6s orbital C. the 5f orbital 7

8 Based on the structure of the periodic table, which orbital becomes occupied first? B. the 6s orbital For a many-electron atom, can we predict unambiguously whether the 4s orbital is lower or higher in energy than the 3d orbitals? A. Yes B. No C. Maybe 8