Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 110	General Chemistry	Fall 2003
Lecture Notes::Lec 22_22 October	© R. Paselk 2003
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The Chemistry of the Elements

The Periodic Table - A Review, cont.

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 they 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.

Trends: Note the trends for

• atomic size: decreases going from left Æ right and from bottom Æ top.
  • Size goes up with atomic number for any individual group.
  • Size decreases irregularly as atomic number increases for any given period (more charge pulls electrons in to nucleus, but shielding reverses as subshells [s or p orbital sets] fill.
• ionization energy: increases from left Æ right and from bottom Æ top.
  • Ionization energy goes down with atomic number for any individual group.
  • Ionization energy increases irregularly as atomic number increases for any given period (more charge pulls electrons in to nucleus, but shielding reverses as subshells [s or p orbital sets] fill.
• electronegativity increases from left Æ right and from bottom Æ top.
• note hydrogen combining ratios (LIH, BeH₂, BH₃, CH₄, H₃N, H₂O, HF) and acid/base properties of oxides (basic for metals, acidic for non-metals)

The Representative Elements

Hydrogen:

• Most abundant element in the Universe (over 90% of the atoms in the Universe, 75% by mass, about 25% helium, everything else is trace).

© R A Paselk

Last modified 23 October 2003