Humboldt State University ® Department of Chemistry

Richard A. Paselk

Science 331
Fall 2004 Lecture/Activity Office: SA560a
Notes: 8 September Phone: x 5719
Home: 822-1116
e-mail: rap1

Chemical Periodicity

Let's look at the Periodic Table of the Elements again. Last time we looked at some examples of element properties, particularly for the alkali metals (group IA) and the halogens (group VIIA), as well as the variation in properties for the elements of Period 3 (Na - Cl). Now let's look at the last group of elements, the Noble Gases and then some terms. We will then look at more general properties.

Terms:

You should know the terminology above and memorize the names and symbols for the elements shown in the table below.

 
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   Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
 Rb Sr                  Ag  Cd   Sn     I  Xe
 Cs  Ba        W        Pt Au  Hg    Pb        

 

What is the basis of the periodicity of properties?

Electrons are held in shells.

Just for fun and your greater wisdom - The modern atom.

Trends: Note the trends for

 

Lewis Structures

Lewis strucutres are a very simple model for representing some chemical properties of atoms. For Lewis structures we assume all atoms above Be want eight electrons in their outermost shells. We represnt the nucleus and all inner electrons as the symbol or "kernal." Outer electrons are then represented as dots for individual electrons (electron bonding pairs may be represented as lines).

Lewis Structures for Atoms: Just show inner "kernel" where symbol stands for nucleus and all inner shell electrons. Only good for Representative elements. For ions the charge is always shown. Thus for metal ions such as calcium the Lewis Structure simply becomes the symbol for the ion. For negative ions such as we see for oxygen (2-) we enclose the ion and its electrons in brackets to indicate that the electrons are all "owned" by the oxygen - it does not share. Examples:

 

Chemical Bonds

Atoms and molecules can be held together by Strong bonds or Weak bonds. We are first going to look at strong bonds.

Covalent vs. Ionic compounds: There are two kinds of strong bonds: ionic bonds and covalent bonds.

We will begin our discussion with ionic bonds since they are easier to understand.

With the representative elements bond formation generally results in the formation of "octets" of electrons in the outermost shell.

Ionic bonds and Ionic Compounds:

Covalent Compounds and Covalent Bonds:


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© R A Paselk

Last modified 8 September 2004