Chemical Reactions and the Periodic Table

Greetings,

Up until now we have looked at chemical reactions and The Periodic Table of the Elements separately.  In this post we'll explore the connection between element reactivity and position on the periodic table.

The relative position of an element on the periodic table is directly related to the likelihood of a reaction happening and even what kind of compound will be formed from a combination of elements.  This is demonstrated in the following diagram.

Notice, in the diagram, the formation of compounds consisting of elements with electron arrangements exactly matching those of noble gases!

Additionally, we find that elements within the same family (vertical column) tend to react in a similar way.  We also can see that there are definite trends in how elements react going down a family of elements and going across the periodic table left to right.

Electronegativity

Central to a discussion of element reactivity is the concept of electronegativity.  Electronegativity is a measure  of the strength of electrical attraction between an element's nucleus and its valence (highest energy) electrons.  Trends in electronegativity going down and across the periodic table produce trends in element reactivity.  The great scientist, Linus Pauling, gets credit for the concept of electronegativity.  He proposed expressing the relative electronegativity of an element as a scale from 0 to 4.  This simple numeric system is based on complex calculations with regard to valence electron behavior in a chemical bond.  Electronegativity values are lowest in the bottom left-hand corner of the periodic table and highest in the upper right-hand corner.  We find that a large difference in electronegativity between a pair of reacting elements tends to produce an ionic compound and values closer to each other (such as pairs of nonmetal elements) tend to produce molecular compounds (This is also indicated in the diagram above).

Element Position vs. Reactivity

Metals tend to be more reactive the further down the periodic table we look.  This is especially true of the Alkali and Alkaline Earth Metals.  Metal elements will likely lose electrons when they react.  Electronegativity decreases as we go down a family of metallic elements.  Lower electronegativity means valence electrons are lost more easily (less energy required) and so we find, for example, that elements further down family IA (such as Cesium) are much more reactive than elements at the top of the same family (such as Lithium).

Conversely, element reactivity increases in the nonmetal portion of the table as we go up, because of increasing electronegativity and its effect on the ease of electron gain.  This is why Fluorine is so much more reactive than Bromine.

That's all for this post.  Thank you for reading!