Electrons in Atoms

1. Electrons in Atoms

2. Bohr Model of the Atom energy level • e- are arranged in orbits around the nucleus • e- have a fixed energy level and cannot exist between energy levels n =4 n =3 n =2

3. Energy Levels • a “quantum” of energy is required to move an e- to a higher level • Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced

4. The Quantum Theory 1. A quantum of energy is the amount of energy required to move an electron from its present energy level to the next higher one. 2. The higher an electron is on the energy ladder, the further it is from the nucleus. 3. Energy levels in an atom are not spaced equally. 4. The further the energy levels are from the nucleus, the more closely spaced they become. 5. The higher the energy level occupied by an electron, the easier the electron escapes from the atom.

5. Atomic Orbitals • Different atomic orbitals are identified by letters. • sorbitals are spherical • p orbitals are dumbbell-shaped

6. Four of the five d orbitals have the same shape but different orientations in space.

7. Orbits (or energy levels) contain a limited number of e- • 1st orbit = 2 e- (s orbital) • 2nd orbit = 8 e- (s and p orbitals) • 3rd orbit = 18 e- (s, p and d orbitals) • 4th orbit = 32 e- (s, p, d and f orbitals)

8. e- Configurations • Arrangement of e- around the nucleus of an atom… • e- enter orbitals of the lowest energy 1st (Aufbau principle) • An atomic orbital may contain only 2 e – with opposite spins (Pauli exclusion principle) • Split up e- in orbitals before they pair up (Hund’s rule)

9. Aufbau Table

10. Aufbau Diagram

13. Orbitals s p d f • Maximum # of 2 6 10 14 e- allowed Energy level 1s1  number of electrons in orbital H ____ 1s orbital 1s2   He ____ 1s first level filled  stable configuration (noble gas)

14. Writing electron configurations: 1s22s22p2 C ___ ___ ___ ___ ___ 1s 2s 2p O ___ ___ ___ ___ ___ 1s 2s 2p 1s22s22p4 1s22s22p6 Ne ___ ___ ___ ___ ___ 1s 2s 2p

15. Writing electron configurations: Na = 11 e- 1s2 2p6 3s1 2s2 1s2 2s2 2p6 3s2 3p3 P = 15 e- 1s2 2s2 2p6 3s2 3p6 4s1 K = 19 e- Pb = 82 e- 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2 [Xe] 6s24f145d106p2

16. ***Exceptions Cr Family and Cu Family: “rob” one electron from an s orbital to fill or half-fill a d orbital Cr [Ar]4s23d4 [Ar]4s13d5 • Mo • [Kr]5s14d5 [Ar]4s13d10 Cu [Ar]4s23d 9 Ag [Kr]5s14d10

17. Electrons • Dual properties (wave and particle) • Ground state - lowest energy level • Energy is needed to raise the e- from the ground state to an excited state • When the e- drops back down to the ground state, light energy is emitted