The Periodic Table

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Electronegativity of some elements are given below for your reference:

            B     C    N    O    F
           2.0   2.6  3.0  3.4  4.0

  Cs              Si   P    S    Cl    Kr   Xe
  0.8            1.9  2.2  2.6  3.2    2.9  2.6

The higher the electronegativity, the more attraction the element has towards bonding electrons. Bonding between two elements with a large electronegativity difference tends to be ionic. It is interesting to note that inert gases \(\ce{Kr}\) and \(\ce{Xe}\) have elenegativities similar to those of nitrogen and carbon.

On the periodic table, there is a general trend. An element close to \(\ce{F}\) has a large electronegativity, whereas an element close to \(\ce{Cs}\) on the opposit corner of the periodic table from \(\ce{F}\) has the least electronegativity.

The Periodic Table as a Summary of Chemical Properties

The periodic table is a convenient way to correlate chemical properties. For example, from their position on the periodic table, we easily recognize them as metals, semimetals (metalloids), or nonmetals.

Most elements are metals (M); the rest are metalloids (o), nonmetals (-), and inert gases (i), on the top right hand of the long periodic table.

   -                              i
   Mo                        o----i
   MM                        oo---i
   MM              MMMMMMMMMMMoo--i
   MMMMMMMMMMMMMMMMMMMMMMMMMMMMoo-i
   MMMMMMMMMMMMMMMMMMMMMMMMMMMMMooi

Look at some metals, and see if you can describe their characteristics. If not, please check some resource books to see if they give a description you like?

Metals are characterized by having a high melting point, high electric and heat conductivity, metallic bonding, being malleable and ductile, forming positive ions \(\ce{Cu^2+}\), \(\ce{Fe^3+}\), and forming alloys with one another. Check out a metal, and you'll be amazed how close it has come to your life.

Nonmetals have low melting points, form molecules, and atoms in their solids are covalently bonded. They are poor conductors of heat and electricity, and they form negative ions or molecular compounds. Here are some non-metals. Note, however, that diamond is an exceptionally good heat conductor, but it does not conduct electricity.

Noble gases: \(\ce{He}\), \(\ce{Ne}\), \(\ce{Ar}\), \(\ce{Kr}\), \(\ce{Xe}\), \(\ce{Rn}\)
Oxygen group: \(\ce{O}\), \(\ce{S}\), \(\ce{Se}\)
Nitrogen group: \(\ce{N}\), \(\ce{P}\), \(\ce{As}\)
Carbon group: \(\ce{C}\), \(\ce{Si}\)
Boron

Between metals and nonmetals lie the metalloids as indicated above.

The chemistry of these elements is best discussed in GROUPS such as alkali metals, carbon group, halogens, inert gases, etc.

Confidence Building Questions

All material exhibit diamagnetism, true or false?

Hint: True, but paramagnetism and ferromagnetism may overcome diamagnetism.

Skill:
Explain what diamagnetism is and how this type of material behaves in a magnetic field.
Atoms of chromium have five 3d electrons. What type of magnetic material is chromium?

Hint: Chromium is a paramagnetic element.

Discussion:
Paramagnetism is due to unpaired electrons in the material.
Which of the alkali elements has the highest ionization energy (IE): \(\ce{Li}\), \(\ce{Na}\), \(\ce{K}\), \(\ce{Rb}\), or \(\ce{Cs}\)?

Hint: \(\ce{Li}\)

Skill
Explain what ionization energy is, and describe the trend for a group of elements.
It takes the most energy to remove an electron from \(\ce{Li}\) in this group. Which of the inert gases has the highest IE: \(\ce{He}\), \(\ce{Ne}\), \(\ce{Ar}\), \(\ce{Kr}\), or \(\ce{Rn}\)?
Which of the following elements releases the most energy when acquiring an electron?
In other words, which has the largest absolute value of electron affinity?

Hint: \(\ce{Cl}\)

Discussion:
The electron affinities are given below:
```
   Cs     C     O     Cl    F
 -45.5  -122  -141  -349  -322 kJ/mol
```
\(\ce{Cs}\) \(\ce{C}\) \(\ce{O}\) \(\ce{Cl}\) \(\ce{F}\)

Hint: \(\ce{F}\)

Discussion:
You should know that \(\ce{F}\) is the most electronegative element, and \(\ce{Cs}\) is the least electronegative. Francium should be, but there is no natural occuring francium because its isotopes are all radioactive.
Should you compare \(\ce{O}\) and \(\ce{Cl}\), which one is more electronegative?

Hint: The Pauling scale electronegativities are: oxygen, 3.4; chlorine, 3.2.

Discussion:
Due to the large electronegativity and the small size of oxygen atoms, oxygen compounds such as water and ethanol form hydrogen bonds.

Contributors and Attributions

Chung (Peter) Chieh (Professor Emeritus, Chemistry @ University of Waterloo)