The Periodic Table

Trends and bonding basics including ionic bonding.

Dr. Melinda Oliver

CHM 101

Groups on the Periodic Table-Pay attention to metals vs nonmetals

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Opposites Attract: Metals lose and nonmetals gain electrons when brought together!

Metals will lose valence electrons to form positive ions-cations and nonmetals will gain electrons to make 8 valence electrons forming negative ions or anions. We will begin with metals that tend to lose ALL of their valence electrons (not true for all metals). The nonmetals are quite predictable-they will always gain to make 8 valence electrons.
Daniel Radcliffe sings "The Elements" - The Graham Norton Show - Series 8 Episode 4 - BBC One

Periodic Trends

The figure to the right shows all of the relevant periodic trends we will be discussing in the course. The most important trend is that for atomic size. The other trends, ionization energy and electronegativity are the exact opposite so if you know the trend for size, you will know the other two trends as well. When we talk about trends on the periodic table, it is understood that we refer to left-->right for horizontal trends and top-->bottom for vertical trends. First, why do atoms vary in size even when they have the same number of shells (horizontal trend)? A video on the development of the periodic table (#7): http://www.learner.org/resources/series61.html?pop=yes&pid=798#
Periodic Trends in Atomic Size
This 18.5 min video starts with explaining the periodic law and then explains in detail how the most important trend of atomic size varies across and down the table.
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Examples from the notes on trends

This 10 min video covers the examples on page 15 of Vol 1 notes.

Dogs Teaching Chemistry - Chemical Bonds
Atomic Hook-Ups - Types of Chemical Bonds: Crash Course Chemistry #22
One more video to further explain bonding. (#8 on the list)

Formulas and Names for Ionic Compounds

  • Metal comes first in formula and in name. Do not change name.
  • Nonmetal comes second in formula and in name. Drop the ending on the nonmetal and add the suffix -ide. So oxygen becomes oxide, fluorine becomes fluoride and so on.
  • Use the CHARGES on each element to predict the formula. We have already been practicing this when we predicted the ion an element would form.
  • Charges must add up to zero. Be careful of the criss-cross method for determining formulas, it does not always work.
  • Example: sodium + nitrogen. Sodium forms a +1 cation and nitrogen forms a -3 anion. In order to be neutral, you need 3 sodiums and one nitrogen in the formula.
  • The name for our example is sodium nitride. PREFIXES ARE NOT USED FOR IONIC COMPOUNDS-ONLY FOR COVALENT COMPOUNDS (di-, tri-, etc).

Polyatomic Ions

These "package" ions are really covalent molecules with a charge. Almost all of them are negative with the exception of a couple. You put them together with other ions exactly as you do the binary types explained above with a few minor variations:


  • do not change any endings! Just state the name of the polyatomic ion.
  • If you need more than one ion, put a parentheses around the formula for the ion.
  • Focus on charge and not the formula for the ion! For example, nitrate has a negative 1 charge. Use this and the charge for sodium (+1) to come up with the formula for sodium nitrate: NaNO3 (3 is subscript). The 3 in the formula for nitrate did not affect how it was combined with sodium.
  • Table of ions: http://www.chemistry.wustl.edu/~edudev/LabTutorials/PeriodicProperties/Ions/ions.html
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Full length video on ionic bonding (lecture 8)

The first part of this video goes through all of the examples on pgs 22 and 23 in the notes. The second half of the video will be used on our next s'more.

What Else Can You Do to Help Your Understanding?

Chemistry is a subject that must be practiced everyday if possible. Work through the lecture examples stopping the video clips and then restarting to check yourself. Take advantage of the online homework in Mastering Chemistry to give you the practice you need to be successful. DO NOT PROCRASTINATE! Check announcements on Sakai everyday and write down due dates from Mastering Chemistry. Keep a printed copy of the most recent course calendar (included in syllabus) next to your work area. Email me with questions!!

Have Questions Later?

If you have trouble opening any links, or just need some clarification...

Dr. Melinda Oliver

University of South Alabama