Electrons in Atoms

1. Electrons in Atoms 5.2 Electron Arrangement in Atoms

2. Chemistry • Today we are learning to:-1. Understand the 3 rules for writing the electronic configuration of elements2. Study some configurations that differ from that expected

3. Electron Configurations • From section 5.1 • Number of sub-levels and depends on principal quantum number • n=1  1 (s-orbital) • n=2  2 (s and p) • n=3  3 (s, p and d) • n=4  4 (s, p, d and f) • A third quantum number, ml, tells us how many of each orbital are allowed: • s-orbital  1 type • p-orbitals  3 types (px, py, pz) • d- orbitals  5 types (dxy, dxz, dyz, dx2, dx2-y2)

4. Electron Configurations The arrangement of electrons in the atom is called the electron configuration. • There are 3 simple rules you must use when deciding which orbitals a set of electrons for an atom will reside in: • The Aufbau Principal • The Pauli Exclusion Principal • Hund’s Rule The Aufbau Principal The aufbau principle states that each electron occupies the lowest energy orbital available.

5. This is an Aufbau diagram. It shows the energy levels of the various atomic orbitals. Orbitals of greater energy are higher on the diagram. Which is of higher energy, a 4d or a 5s orbital? Note that: all 2p orbitals have the same energy, as do all 4f orbitals etc. Orbital types with the same p.q.n. Increase in energy and can overlap with other orbitals.

6. Electron Configurations Aufbau rule 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f • In order to find out what order the orbitals are filled in: • draw out this diagram in your note book. • With a pencil draw a diagonal line through each possible orbital • Start at the top right to go through 1s to bottom left • Below the first line start at top right again to go through 2s • Repeat the process though all orbitals

7. Electron Configurations Pauli Exclusion Principle The Pauli exclusion principle states that a maximum of two electrons can occupy a single orbital, but only if the electrons have opposite spins. Hund’s Rule Hund’s rulestates that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same energy level orbitals.

8. spdf notation for H, atomic number = 1 1 no. of s 1 electrons value of l value of n Writing Atomic Electron Configurations Two ways of writing electronic configurations One is called the spdf notation.

9. Writing Atomic Electron Configurations Two ways of writing electronic configurations Other is called the orbital box notation.

11. 5.2 • Orbital Filling Diagram

12. Electron Configurations 1s 2s 2p 3s 3p

16. for Conceptual Problem 1.1

17. 5.2 Exceptional Electron Configurations • Exceptional Electron Configurations • Why do actual electron configurations for some elements differ from those assigned using the aufbau principle?

18. 5.2 Exceptional Electron Configurations • Some actual electron configurations differ from those assigned using the aufbau principle because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations.

19. 5.2 Exceptional Electron Configurations • Exceptions to the aufbau principle are due to subtle electron-electron interactions in orbitals with very similar energies. • Copper has an electron configuration that is an exception to the aufbau principle.

20. 5.2 Section Quiz. • 1. Identify the element that corresponds to the following electron configuration: 1s22s22p5. • F • Cl • Ne • O

21. 5.2 Section Quiz. • 2. Write the electron configuration for the atom N. • 1s22s22p5 • 1s22s22p3 • 1s22s1p2 • 1s22s22p1

22. 5.2 Section Quiz. • 3. The electron configurations for some elements differ from those predicted by the aufbau principle because the • the lowest energy level is completely filled. • none of the energy levels are completely filled. • half-filled sublevels are less stable than filled energy levels. • half-filled sublevels are more stable than some other arrangements. `

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