CHEM 119 Fall 2026 - Chapter 7 with a hint of Chapter 8 (10162026)
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Overview
Alicia Altemose explains the four quantum numbers, orbital shapes and orientations, electron capacity, and node patterns, then applies the rules to quantum-number checks and orbital-count problems. She begins Chapter 8 electron configurations with lithium and periodic-table blocks, and notes that the next exam is Wednesday, with Chapter 8 homework questions 9 and 14 through 20 excluded if they are not covered in class.
Key takeaways
- Quantum-number validity is checked in sequence: l must satisfy 0 ≤ l ≤ n − 1, then m_l must fall between −l and +l; m_s is always either −1/2 or +1/2.
- A subshell with angular momentum number l contains 2l + 1 orbitals, so s, p, d, and f subshells contain 1, 3, 5, and 7 orbitals respectively.
- Each orbital holds at most 2 electrons with opposite spins; therefore, the n = 2 shell holds 8 electrons and the n = 3 shell holds 18.
- The four quantum numbers progressively identify a shell, subshell, specific orbital, and individual electron; for n = 2, the possible count narrows from 8 electrons to 6, then 2, then 1.
- An orbital has n − 1 total nodes, while the number of planar nodes equals l; consequently, 3p has 2 total nodes, consisting of 1 planar and 1 radial node.
- Exam preparation includes timed problem practice, and Chapter 8 homework questions 9 and 14 through 20 may be excluded from Exam 2 if class does not reach them.
Chapters
- A mock exam for Exam 2 is posted at the top of the exams module, with its answer key planned for the weekend.
- Alicia Altemose recommends timed practice because students felt rushed on the previous exam.
- Exam 2 is scheduled for Wednesday next week; Chapter 8 homework is due Monday night, and questions 9 and 14 through 20 may be excluded if not covered.
- Extra credit survey 3 is due Monday, with drop-in help after class and Monday, plus a dedicated Zoom review Tuesday at 10:30 a.m.
- The principal quantum number n is a positive whole number and describes an electron's shell, orbital size, and energy.
- The angular momentum quantum number l ranges from 0 to n minus 1, so l can never equal n.
- The l-to-subshell mapping is 0 = s, 1 = p, 2 = d, and 3 = f; s, p, and d orbitals are introduced as spheres, figure-eights, and clovers.
- The magnetic quantum number m_l ranges from negative l through zero to positive l, distinguishing orbital orientations within a subshell.
- A brief class poll names a calf, then Altemose uses a table to show that n = 1 allows only l = 0, while n = 2 allows l = 0 or 1.
- The number of m_l values is 2l + 1: s has 1 orbital, p has 3, d has 5, and f has 7.
- For n = 4, the allowed l values are 0, 1, 2, and 3; m_l must be checked against l rather than directly against n.
- In an allowable-quantum-number exercise, option D is the only valid choice; invalid choices can be repaired by setting m_l within the range from negative l to positive l.
- The spin quantum number m_s has only two values, negative one-half and positive one-half, often represented by down and up arrows.
- Each orbital holds at most 2 electrons, and two electrons in the same orbital must have opposite spins.
- Neutral lithium has 3 electrons, arranged as 1s² 2s¹ by filling the lowest-energy orbital first.
- Two electrons cannot share all four quantum numbers, so electrons in the same orbital differ in m_s.
- For a 5p orbital, the number specifies n = 5 and the p designation specifies l = 1.
- Because l = 1, m_l must be negative 1, 0, or positive 1; a proposed value outside that range is invalid.
- The exercise distinguishes a valid 5p set from other allowed sets that instead describe a 6p or 5d orbital.
- When no other electron in the same orbital is specified, either m_s value, negative or positive one-half, is possible.
- For n = 2, the 2s subshell holds 2 electrons and the three 2p orbitals hold 6, giving the shell a total capacity of 8 electrons.
- Knowing n narrows the location to a shell; adding l identifies a subshell, adding m_l identifies one orbital, and adding m_s identifies one electron.
- The sequence of possible electron counts for n = 2 is 8 at the shell level, 6 for the 2p subshell, 2 for a single 2p orbital, and 1 for a specified spin.
- Squared wave functions represent the probability of finding an electron; higher-n examples such as 3s and 3p extend farther from the nucleus.
- For n = 3, the allowed subshells are 3s, 3p, and 3d because l can be 0, 1, or 2.
- Their orbital counts are 1 for 3s, 3 for 3p, and 5 for 3d, for 9 orbitals total.
- With 2 electrons per orbital, the n = 3 shell can hold 18 electrons: 2 in 3s, 6 in 3p, and 10 in 3d.
- Nodes are regions with zero electron density; the 3s orbital has 2 nodes because the total node count is n minus 1.
- An s orbital has no planar nodes because l = 0; p orbitals have 1 planar node, and d orbitals have 2.
- A 3p orbital has 2 total nodes: 1 planar node from l = 1 and 1 radial node.
- An electron can absorb light and move to a higher-energy orbital; the example shows hydrogen moving from 1s to 3p.
- Hydrogen energy levels are not split by shielding from other electrons because a hydrogen atom has only one electron.
- The periodic table's s block holds 2 electrons per s subshell, while the p block holds 6 per p subshell.
- Electron configurations are filled from left to right and top to bottom across the periodic table; Chapter 8 continues Monday.
Transcript excerpt
0:08 Howdy. All right. Good morning. How are we doing today? Pretty good. Happy Friday. So, uh, if you didn't see my announcement yesterday, there is a mock exam for exam 2 posted. It's like right at the top of the exams module. I'll post the answer key over the weekend so that you can work on it, try it before you know the answers. Um, I also gave some tips on how you can study hopefully more effectively if if needed. Um, setting a timer when you study or when you practice is really important because I know a lot of you were feeling the time for the last exam. Um, so make sure you time yourself and get faster and faster at doing those problems.
0:57 Um, so exam two is on Wednesday next week. So, uh, we will see how far we get with chapter 8 today. Um, if we don't get to the content on number nine from the chapter 8 homework or numbers 14 through 20, uh, that won't surprise me. Um, and that material won't be on exam two. Uh, but everything else in that chapter 8 homework might be on exam two. Um, we will get through most of it today and uh I want the exam the chapter 8 homework will still be due Monday night but I might reopen it afterwards. Like I want it due Monday night so that you practice before the exam but I might reopen it um if we don't get to all of it. Um so if you don't get to those numbers that's fine. I'll reopen it and
1:47 you can do it again. Um so the reminder the exam the extra credits number three that one that reflection survey that's due on Monday and that is under there's a new extra
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Related notes
Summary, takeaways, and chapters were generated by AI from the video's transcript and may contain errors. The video belongs to its creator, Alicia Altemose.