Chapter 8 Chemical Bonding Pages 224 - 249 Section 2

Ionic Bonding An ionic bond forms when valence electrons are transferred from one atom to another atom.

Like all chemical bonds, ionic bonds form so that the outermost energy levels of the atoms in the bonds are filled. In an ionic bond, one atom has lost electrons and the other atom has gained electrons.

Charged Particles Atoms are neutral because the number of electrons (-) are equal to the number of protons (+). A transfer of electrons between atoms changes the number of electrons in each atom. The negative and positive charges no longer cancel out, and the atoms become ions.

Positive Ions The atoms that lose electrons in an ionic bond form positive ions because they have more protons (+) than electrons (-). When metal atoms bond with other atoms, the metal atoms tend to lose these valence electrons and form positive ions. 12 Mg Mg++ 12

Negative Ions During chemical changes, some atoms gain electrons from other atoms. The ions that form have more electrons (-) than protons (+) and have an overall negative charge. Cl Cl- -

Negative Ions (con’t) Chlorine atoms have seven valence electrons and need only one more to have a full set (8) of valence electrons. When the chlorine atom gains an electron it becomes a chloride ion. Notice that the name of the negative ion formed from chlorine ends with ide.

Forming Ionic Compounds When ionic bonds form, the number of electrons lost by the metal atoms equals the number of electrons gained by the nonmetal atoms. The resulting ionic compound is neutral and has different properties than the metal and the nonmetal atoms that make it up. Crystal lattice – a three-dimensional repeating pattern.

Properties of Ionic Compounds The strong electromagnetic attraction between the positive and negative ions in a crystal lattice gives ionic compounds certain physical properties: Brittle, high melting points, high boiling points, high solubility (dissolve easily) in water.

Let’s Try It Lab: How Do Ions Form?