Electrons in Atoms

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

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

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.

Atomic Orbitals  Different atomic orbitals are identified by letters.  s orbitals are spherical  p orbitals are dumbbell-shaped

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

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)

e - Configurations  Arrangement of e - around the nucleus of an atom… 1)e - enter orbitals of the lowest energy 1 st (Aufbau principle) 2)An atomic orbital may contain only 2 e – with opposite spins (Pauli exclusion principle) 3)Split up e - in orbitals before they pair up (Hund’s rule)

Aufbau Table

Aufbau Diagram

 Orbitals s p d f  Maximum # of e - allowed H____ 1s Energy level number of electrons in orbital orbital He____ 1s   first level filled  stable configuration (noble gas) 1s11s1 1s21s2

Writing electron configurations: C___ ___ ___ ___ ___ 1s 2s 2p Ne ___ ___ ___ ___ ___ 1s 2s 2p O___ ___ ___ ___ ___ 1s 2s 2p 1s 2 2s 2 2p 2 1s 2 2s 2 2p 4 1s 2 2s 2 2p 6

Writing electron configurations: Na = 11 e - 1s21s2 2s22s2 2p62p6 3s13s1 P = 15 e - K = 19 e - Pb = 82 e - 1s21s2 1s21s2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 2 [Xe] 6s 2 4f 14 5d 10 6p 2 2s22s2 2p62p6 3p33p3 2s22s2 2p62p6 3s23s2 3p63p6 4s14s1 3s23s2

***Exceptions Cr Family and Cu Family: “ rob ” one electron from an s orbital to fill or half-fill a d orbital Cr [Ar]4s 2 3d 4  Ag[Kr]5s 1 4d 10 [Ar]4s 1 3d 10 Cu [Ar]4s 2 3d 9  Mo [Ar]4s 1 3d 5 [Kr]5s 1 4d 5

 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 Electrons