Nace CP 1 - Compounds (Molecules); Ions; The Bohr Model of an Atom

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Basic Chemistry and Basic Corrosion Theory 2:2

CP 1 – Cathodic Protection Tester Course Manual

02/01/05

ELECTRONS

UCLEUS

ORBIT

Figure 2.1 The Bohr Model of an Atom

Ions

Gaining or losing electrons can electrically charge atoms. Electrically

charged atoms are referred to as ions and the charge on an atom is known as

its valence state. An ion formed by the gaining of electrons is called an

anion and is negatively charged because the number of electrons is greater

than the number of protons. The loss of electrons yields a positively

charged ion called a cation. For example, when sodium combines with

chlorine an electron is transferred from sodium to chlorine, creating a

positively charged sodium ion and a negatively charged chloride ion. The

two ions, now of opposite charge, are electrostatically attracted to each

other, forming a molecule. Ions allow for transfer of electrical charge in

liquids.

Compounds (Molecules)

Molecules are composed of two or more atoms. A molecule is the smallest

unit of a substance with the same specific chemical properties of that

substance. For example, a single water molecule is composed of one oxygen

and two hydrogen atoms as shown in Figure 2.2. Further splitting of this

molecule would result in a substance with characteristics unlike water. The

atoms of a molecule are held together by a force referred to as chemical

bonding. It is this chemical bonding that defines many of the properties of a

substance.