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This chapter discusses the fundamental principles of electron configurations within atoms. Electrons occupy various energy levels and sublevels, each with a distinct number of orbitals that dictate electron placement. Key rules governing electron configurations, including the Aufbau Principle, Pauli Exclusion Principle, and Hund’s Rule, are explored. Additionally, the order of orbitals in the periodic table is detailed, enabling a clear understanding of how to write electron configurations for elements. Accurate configurations are crucial for studying chemical properties and behaviors.
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Electrons in Atoms Chapter 5
Electron Configurations • So, you live on Aspen St., but what is your exact address? • We know that electrons can occupy energy levels, but they can also reside within sublevels. • Each level has a fixed number of sublevels and each sublevel has a fixed number of electrons
Block Table • This shows the different blocks in the Periodic Table. • It also shows in what order to write electron configurations (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d,7p)
Rules • 1. Aufbau Principle – fill lowest energy levels first • 2. Pauli Exclusion Principle – only two electrons in an orbital with opposite spins • 3. Hund’s Rule – (bus seat rule) place one electron in each orbital before placing the second
How do we write an electron configuration? • H • He • Be • B • Kr
4d 5s 4p 3d 4s s 1 2 p 1 3p 1 2 3 4 5 6 2 d 3 3s 1 2 3 4 5 6 7 8 9 10 4 5 2p 6 7 2s H f 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1s1 That’s right: it goes in the 1s sublevel. And its el. config is 1s2. Notice in the table above where H is – in the area designated as 1s. So where does the next electron go? 1s +
4d 5s 4p 3d 4s s 1 2 p 1 3p 1 2 3 4 5 6 2 d 3 3s 1 2 3 4 5 6 7 8 9 10 4 5 2p 6 7 2s He f 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1s2 If you were thinking it went in the 2s, then you forgot that each orbital can hold up to two electrons. Note how He is right here in the area designated as 1s2 and so its el. config. is 1s2. 1s +
4d 5s 4p 3d 4s s 1 2 p 1 3p 1 2 3 4 5 6 2 d 3 3s 1 2 3 4 5 6 7 8 9 10 4 5 2p 6 7 2s Be f 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1s2 2s2 Is this what you were thinking? Good. Now look at the periodic table above, what comes after the 2s sublevel? 1s The 2p sublevel. So what will the next el. conf. be? +
4d 5s 4p 3d 4s s 1 2 p 1 3p 1 2 3 4 5 6 2 d 3 3s 1 2 3 4 5 6 7 8 9 10 4 5 2p 6 7 2s B f 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1s2 2s2 2p1 Is this what you were thinking? Notice how B is in the 2p1 spot. 1s So its full el. conf. is 1s2 2s2 2p1. What’s next? +
4d 5s 4p 3d 4s s 1 2 p 1 3p 1 2 3 4 5 6 2 d 3 3s 1 2 3 4 5 6 7 8 9 10 4 5 2p 6 7 2s Kr f 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 1s +