Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2011

Lecture Notes 24: 23 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) and first ionization energy. Today we continue with the trend for electronegativity, which is an indication of how electrons are shared by atoms in bonds.

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

Periodic Table with Electronegativity Trend arrow

plot of electronegativity vs. atomic number demonstrating periodicity

Highest Densities

periodic table with highest density elements indicated by period

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.

Note hydrogen combining ratios (LIH, BeH2, BH3, CH4, H3N, H2O, HF) and acid/base properties of oxides (basic for metals, acidic for non-metals)

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 23 March 2011