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Section 4: Electron Configurations
1sorbital
2sorbital
2porbitals
3sorbital
Nucleus
Electron energy levels have sublevels of different shapes
3 principles Describe the electron configurationof any atom:•the aufbau principle•the Pauli exclusion principle•and Hund’s rule
Electron Configurations:location of e–’s in different orbitals
How do electrons fill these orbitals?
Aufbau Principle
(building up), electrons fill the orbitals of lowest energy first.
Pauli Exclusion Principle
an atomic orbital may describe at most two electrons that must have opposite spins; that is, the electron spins must be paired.
↑↓s
Hund’s Rule
electrons occupy orbitals of the same energy with as many of the same spin as possible before opposite spin.
↑↑ ↑↓↓px py pz
↓
Element # of electrons
Orbital notation Electron configuration
Lithium 3 ____ ____ ____ ____ ____ 1s 2s 2p
1s22s1
Beryllium 4 ____ ____ ____ ____ ____ 1s 2s 2p
1s22s2
Boron 5 ____ ____ ____ ____ ____ 1s 2s 2p
1s22s22p1
Carbon 6 ____ ____ ____ ____ ____ 1s 2s 2p
1s22s22p2
Nitrogen 7 ____ ____ ____ ____ ____
1s 2s 2p
1s22s22p3
Oxygen 8 ____ ____ ____ ____ ____ 1s 2s 2p
1s22s22p4
Fluorine 9 ____ ____ ____ ____ ____ 1s 2s 2p
1s22s22p5
Neon 10 ____ ____ ____ ____ ____ 1s 2s 2p
1s22s22p6
2s21s2 3s23p32p6
Write the electron configuration for phosphorus (P):
nucleus
Write the electron configuration for phosphorus (P):
nucleus
2s21s2 3s23p32p6
valence electrons:e–’s in the outer most (highest) energy level
How many valence e–’s in phosphorus (P)? 5
nucleus
Write the electron configuration for Krypton (Kr):
2s21s2 2p6 3p63s2 4p64s2 3d10
nucleus
Write the electron configuration for Krypton (Kr):
2s21s2 2p6 3p63s2 4p64s2 3d10
valence electrons:e–’s in the outer most (highest) energy level
How many valence e–’s in Krypton (Kr)? 8
1. Identify the element that corresponds to the following electron configuration: 1s22s22p63s2
A. Ca
B. Ne
C. Na
D. Mg
Quick Quiz!
Quick Quiz.
2. Write the electron configuration for the atom N.
A. 1s22s22p5
B. 1s22s22p3
C. 1s22s1p2
D. 1s22s22p1
Quick Quiz.
3. What is the first (lowest-numbered) principal energy level in which p orbitals are found?
A. 1
B. 2
C. 3
D. 4
• The period number tells you the energy level (remember, the d block is one energy level lower).
• The group # tells you the # of valence electrons.
• Group 1 elements have 1.
• Group 7A have 7.
Electron Configurations and the Periodic Table
Noble Gas Core Configuration
Na: 1s2 2s2 2p63s1
Ne: 1s2 2s2 2p6
Noble gas e- config for Na:
[Ne]3s1
Ne
Noble Gases are group 18
4p12s21s2 2p6 3p63s2 4p14s23d10
OR 4s2[Ar] 3d10
Write the full electron configuration for Gallium (Ga), atomic number 31.
Ar
Phosphorus (P):
Lewis dot diagrams
[Ne]3s2 3p3
1s2 2s2 2p6 3s2 3p3
# valence e–’s: ___
Group # : ___
5
5A
P
Lewis dot diagram:
• valence e–’s are shown as dots around the symbol of the element
Lewis dot diagrams
Bromine (Br):
[Ar]4s2 3d10 4p5
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
# valence e–’s: ___
Group # : ___
7
7ALewis dot diagram: Br
• valence e–’s are shown as dots around the symbol of the element
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