Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2013

Lecture Notes 24: 27 March

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Trends in Chemical Periodicity

(plots ©1994 Hanson, Harper, Paselk, & Russell)

Last time we looked at the trends for atomic radii (atomic size). Today we continue with the trend for first ionization energy (the energy needed to strip the outermost electron from a free atom) and electronegativity (an indication of how electrons are shared by atoms in bonded atoms).

First ionization energy: increases from left right arrow right and from bottom right arrow top.

Periodic Table with ionization energies Trend arrow

plot of first ionization energy vs. atomic number demonstrating periodicity

 

Electronegativity increases from left right arrow right and from bottom right arrow top.

Group ! elements have the least tendency to attract bonding electrons, while F has the greatest attraction for electrons in bonds.

Periodic Table with Electronegativity Trend arrow

plot of electronegativity vs. atomic number demonstrating periodicity

Note and memorize the electronegativities for H (2.1) and the elements of the second Period (Li {1.0}, Be {1.5}... F {4.0})

Highest Densities

periodic table with highest density elements indicated by period

Note, elements are near "center" of each Period. Due to a combination of nuclear mass, size and packing in crystals.

Highest Melting Points

periodic table with highest melting point elements by period

Due to multiple strong covalent bonds in Representative elements, and strong "covalent-metallic" bonding via unfilled d orbital electrons in Transition elements.

What is the basis of the periodicity of properties?

Electrons are held in shells.

 

Electronic Configurations & Periodicity

There are a number of different notation conventions for electronic configurations:

Spectroscopic notation

Note that when we get to the d electrons they are added to the next inner orbital - they are added inside the atom and are not outermost! Note also that you may write them in the order they show up on the Periodic Table, or, if you prefer, you may group them by shell. You may also wish to use a tool to help you remember this pattern of filling:

The Aufbau Principle

Orbital Filling Diagrams

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© R A Paselk

Last modified 27 March 2013