Chapter 8 Electronic Configuations and Periodicity

Electronic Structure of Atoms

• Electron Spin, Pauli Exclusion Principle
• Building up Principle (Aufbau)
• Electron Configurations
• Orbital Diagrams and Hund's Rule

Periodicity of the Elements

• Mendeleev's Predictions
• Periodic Properties
• Periodicity in Main Group Elements

Oxides

e^- config.

Oxidation numbers

Objectives

• write the electron configuration for any element using the Aufbau Principle, the Pauli Exclusion Principle, and Hund's Rule.
• Know the number of sublevels and orbitals in each main energy level.
• identify the s, p, d and f block elements.
• use orbital diagram representations of electron configurations to predict the number of unpaired electrons in an element.
• describe the concept of electron spin

Quantum Mechanics allows for the calculation of relative energies for the various orbitals. These energies have been verified by experimental spectroscopy.

The AufBau Principle

• The Aufbau Principle states that electrons will fill lowest energy orbitals first following the Pauli Exclusion Principle and Hund's Rule.

Pauli Exclusion Principle

• No two electrons in an atom may have the same four quantum numbers. (only two electrons in any one orbital)

Hund's Rule

• Electrons will maintain the maximum number of unpaired electrons in degenerate orbitals. (in orbitals of the same energy, electrons will not pair up until forced to)

Order of Orbital Filling

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f ...

6s 6p 6d ... ... ...

7s ... ... ... ... ... ...

Using the periodic table, s, p, d and f-blocks

Show electrons for the following using the "n, l" and the orbital diagram or"box" conventions.

Li 1s² 2s¹

Li

K 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

K

O

O

Se

Se

Look at the outermost shell, the Valence Shell

• Examples- Noble Gas Short-cut
• Mg
• Sr
• Cl
• Br
• Sn
• Pb

Electron Configurations of Special Atoms and Ions

• Pb
• Pb⁺²
• Pb⁺⁴
• Fe
• Fe⁺²
• Fe⁺³
• Cu
• Cr

From Chem Cards

Periodicity of the Elements

Periodic trends can be explained by looking at the electron configurations of the elements.

Atomic Radius-

• trend:

Ionic radii-

• cations
• anions

Electronegativity-

• trend

Ionization Energy-

• trend-
• 2nd and third I.E.'s

Electron Affinity

Properties

Metals

• Lustrous
• Malleable and ductile- may be pounded into shapes or drawn into wires
• Good thermal and electrical conductivity
• All are solid except Hg (Cs and Ga have low m.p.s)
• Some melt at very high temp. mp of Cr = 1900ºC

Most metal oxides are basic

• MgO + H₂O ——> Mg(OH)₂

Most metal compounds are ionic solids

Exist is solutions mainly as cations

Metal Reactivity-

• trend-

Nonmetal Properties

• Not lustrous, variety of colors
• Solids are usually brittle, may be hard or soft
• Most nonmetal oxides are acidic in solution

SO₂ + H₂O ——> H₂SO₃

• Most are molecular compounds
• Exist in solutions as anions or oxy anions Cl^-, ClO₃^-
• Nonmetals vary in mp, bp. hardness etc.

Non-metal Reactivity-

• trend
•  
•  
•  
•  
• Reactions

Metal + nonmetal ––> salt

metal oxide + water ––> base

nonmetal oxide + water––> acid

metal oxide + acid ––> salt + water

Na₂O + HCl -->

nonmetal oxide + base ––> salt + water

CO₂ + Ca(OH)₂

nonmetal oxide + metal oxide––> salt

Na₂O + CO₂

Trend Summary

Most active metals have the most metallic character - near cesium

Most nonmetallic elements are near fluorine

Metals have low ionization energy and form positive ions

Nonmetals have high ionization energy and most negative E.A. and form negative ions (highest electronegativity near fluorine)

Periodicity in Main Group Elements

Oxides

e^- config.

Oxidation numbers

• • 1. 
    2. From Chem Cards
    3. 
    4. 
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