Atomic Theory

ATOMIC THEORY
Lesson 3 - Page 4

Lewis dot system of hydrogen and carbon

Lewis’ dot system compared to Couper’s dash
system of showing bonding

Lewis also developed another system for representing chemical bonds by using the electron dot system. Each atom is represented by its chemical symbol with the number of electrons in its outermost shell or valence electrons. The formula of a compound, can be represented by showing how two or more atoms share electrons with each other.

Van der Waals

Bonds are not only restricted to a single bond. For example, Ethylene has a double bond shown as double dots or dashes. Acetylene has a triple bond shown by triple dots and dashes.

Johannes Diderick Van der Waals (1837-1923), a Dutch scientist discovered that molecules are attracted by yet another force. Van der Waals force is another type of chemical bonding. Such forces exist between particles that appear to be electrically neutral. This type of bond is very weak.

There are other ways to describe some of the bonds, especially under covalent bonding including metallic and hydrogen bonds. The atoms that comprise a metal, for example, are held together by a metallic bond. A metallic bond is one in which all of the metal atoms share with each other a cloud of electrons. A hydrogen bond is a strong bond, but weaker than a covalent bond. It involves the attraction that exists between two atoms or ions with an electronegative charge with nitrogen, oxygen, and fluorine. Water is an example of this type of bond. The hydrogen end is slightly positive and the oxygen end, slightly negative. They are attracted. Hydrogen bonds are very common and extremely important in biological systems.

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