Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109	General Chemistry	Summer 2002
Lecture Notes:: 27 June	© R. Paselk 2002
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Atomic Structure & Chemical Periodicity, cont.

The Periodic Table

Look at the Periodic Chart on the wall. The pattern arises due to a repetition or periodicity of chemical properties. The vertical columns of the charts are called groups, while the rows are referred to a periods.

Note the numbering of the groups. The numbers from 1 - 18 are the internationally accepted numbers. We will also use the I - VIII "American" numbering system. Note that the "tallest" columns comprise what are referred to as the "representative elements" (IA - VIIIA).

Terms:

• Period: the rows of elements showing a repeating pattern of properties (e.g. Na - Ar).
• Group: a vertical column of elements on the table sharing a family resemblance of properties (e.g. Li - Fr).
• Representative elements: the elements of the s-block and p-block (blue and green on the table below).
• Transition metal elements: the elements of the d-block (yellow in the table below).
• Inner-transition metal elements: The f-block or Lanthanides and Actinides (not shown on the table below)
• Groups:
  • IA = alkali metals;
  • IIA = Alkaline earth metals;
  • VIIA = Halogens (note the generic symbol of X standing for any halogen);
  • VIIIA = Noble gases (older = inert gases).

You should know the terminology above.

Periodic Table of the Elements  IA IIA IIIA IVA VA VIA VIIA VIIIA    H  He Li Be    B C N O F Ne Na Mg IIIB IVB VB VI VIIB VIIIB IB IIB  Al Si P S Cl Ar K Ca Sc  Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr  Rb Sr  Y Zr Nb Mo Tc Ru Rh Pd  Ag  Cd  In Sn Sb Te I  Xe  Cs  Ba Lu  Hf Ta  W Re Os Ir  Pt Au  Hg Tl  Pb Bi Po At Rn

Let's look at some of the elements and see what their properties are like:

• Group IA, on the left side of the chart, is known as the alkali metals because the react with water to produce strong bases (a base is alkaline). Note that all of them are soft (cut with a butter knife), low density (Li floats on oil, Na and K float on water), very reactive metals. All of them react with water with Li<Na<K<Rb<Cs. In each case the metal gives its electron to water leaving hydroxide ion (OH^- a base) and hydrogen gas. For example with sodium:

• Group VIIA, on the right side of the chart, is known as the halogens. The halogens form acids with water, are gases at the top of the Periodic Chart and high vapor pressure liquids, then solid going down; exist as diatomic molecules (X₂), and are very reactive towards metals. For example sodium reacts violently with chlorine gas to give table salt (NaCl):

• Group VIII is known as the Noble Gases, or sometimes the Inert Gases because until the 1960's they had no known compounds. Very unreactive. The only known compounds of the Noble gases are with very reactive elements like F and O, and even they don't form compounds with smaller Noble gases such as He and Ne.
• Look at the elements of Period 3 (Na - Cl) Note how their properties change from metallic to non-metallic.

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