Ions and Ionic Bonds

Formation of Ions

Atoms can gain or lose electrons to achieve a stable electron configuration, typically resembling a noble gas. When an atom gains electrons, it becomes a negatively charged ion called an anion. When an atom loses electrons, it becomes a positively charged ion called a cation.

Formation of Positive Ions (Cations)

Metals tend to lose electrons to form positive ions. The number of electrons lost corresponds to the group number of the metal in the periodic table. For example, sodium (Na) in Group 1 readily loses one electron to form a sodium ion (Na⁺).

The process of losing electrons results in a positive charge on the atom, hence the name "cation".

Formation of Negative Ions (Anions)

Non-metals tend to gain electrons to form negative ions. The number of electrons gained is usually equal to the number of electrons needed to complete the noble gas electron configuration. For example, chlorine (Cl) in Group 17 readily gains one electron to form a chloride ion (Cl^-).

The process of gaining electrons results in a negative charge on the atom, hence the name "anion".

Atom	Electrons (Shell Configuration)	Charge	Ion Formed
Sodium (Na)	$2, 8, 1$	+1	Na+
Chlorine (Cl)	$2, 8, 7$	-1	Cl-
Oxygen (O)	$2, 8, 2$	-2	O2-
Magnesium (Mg)	$2, 8, 2$	+2	Mg2+

Summary:

• Metals form positive ions (cations) by losing electrons.
• Non-metals form negative ions (anions) by gaining electrons.

Key Terms

• Ion: An atom or molecule with a net electrical charge.
• Cation: A positively charged ion.
• Anion: A negatively charged ion.