Electron ConfigurationChemical Bonding

Amalene Cooper-Morgan, Ph.D.

General Ordering for Multi Electron Atoms

Recall…• Remember • S sublevel holds 2 electrons• P sublevel holds 6 electrons• D sublevel holds 10 electrons• F sublevel holds 14 electrons

Electron Configuration for Bromine

Use Noble Gases to Represent Inner Electrons

Valence Electrons• Located in the outermost principal energy level• For transition elements, d electrons are counted among the valence

electrons, although they aren’t in the outermost principal energy level• Core electrons are electrons in complete principal energy levels

Valence vs Core Electrons

Main Group Elements• Don’t include transition elements• Valence electrons are in their outermost principal energy level• Example:• Germanium, atomic number 32 is a main group element• Ge n=1, 2 and 3 principal energy levels are complete (Core electrons)• Ge n=4 is the outermost principal level (Valence electrons)

Electron Configuration for Ge

Principal Quantum Number

Orbital blocks of the Periodic Table

Except for the transition metals, main group elementss valence electrons are equal to the lettered groupe.g Chlorine has 7 valence electrons and it’s in group 7A

Periodic Trends- Size of atoms and Effective Nuclear Charge• Orbitals do not represent a physical boundary but a statistical

probability distribution of where to find an electron• Non bonding atomic radius or van der Waals radius- is the radius of an

atom when it is not bonded to another atom

Periodic Trends- Size of atoms and Effective Nuclear Charge• Bonding atomic radius or covalent radius• Non-metals- ½ the distance between 2 of the atoms bonded together• Metals- ½ the distance between 2 of the atoms that are next to each other in

a crystal of a metal

Exceptions..• Bonding radii of He and Ne are approximated• They do not form either chemical bonds or metallic crystals

Atomic Radius• Average bonding radii• Radius of an atom when its bonded to another atom• Always smaller than van der waals radius

Approximate bond length• Sum of the atomic radii for 2 covalently bonded atoms• Approx. bond length for ICl:• I atomic radius = 133 pm + Cl atomic radius = 99 pm• Total bond length = 232 pm• Actual bond length is 232.07 pm

Trends across periodic table• Atomic radii peak with Alkali metals• Atomic radii is mainly determined by the valence electron• As we move• down a column, atomic radius decreases

Effective Nuclear Charge or Net Charge

Screening and Effective Nuclear Charge

Core electrons = 1s2 electronNucleus = 3+ Zeff ~ (3+) – 2 ~ 1+

Trends across the Periodic Table for Effective Nuclear Charge

Trends across periodic table• As we move across a row to the right the atomic radius decreases• Transition elements, except the first couple of elements in a column,

do NOT follow the same trend for atomic radii as main group elements• Atomic radius does not decrease as you cross the row from L to R• Atomic radii stay constant• The outermost electrons stay constant and experience a constant nuclear

charge, keeping the radius approx. constant