Chapter 6 Chemical Bonds

Overview In this chapter, we will be studying 2 primary types of chemical bonds. One: ionic bonds Two: covalent bonds We will also learn how to name various compounds.

Formation of Ions When an atom gains or loses an electron, the number of protons is no longer equal to the number of electrons. The charge of the atom is not balanced and the atom is not neutral. Ion: an atom that has a net positive or negative electric charge.

2 Types of Ions Anion: an ion with a negative charge. Cation: an ion with a positive charge. Example: Cl - is the chloride ion. Example: Na + is the sodium ion.

Formation of Ionic Bonds Ionic bond: the force that holds cations and anions together. Ionic bonds form when electrons are transferred from one atom to another.

Chemical Formula Def: a notation that shows what elements a compound contains and the ratio of the atoms or ions of these elements in the compound. Example: NaCl (sodium chloride)

Covalent Bonds Def: a chemical bond in which two atoms share a pair of valence electrons. When two atoms share one pair of electrons, the bond is called a single bond. When two atoms share two pairs of electrons, the bond is called a double bond. When two atoms share three pairs of electrons, the bond is called a triple bond.

Naming Ionic Compounds Pattern: the name of the cation followed by the name of the anion (Fig. 16, p. 171). The name for the cation is the name of the metal without any change. The name for the anion uses part of the name of the nonmetal with the suffix –ide.

Metals with Multiple Ions The alkali metals (1A), alkaline earth metals (2A), and aluminum (3A) form ions with positive charges equal to the group number. Potassium: K + Calcium: Ca +2 Aluminum: Al +3

Writing Formulas for Ionic Compounds If you know the name of an ionic compound, you can write its formula. Step 1: Write the symbol of the cation (+) first, followed by the symbol of the anion (-). Step 2: Use subscripts to show the ratio of ions in the compound.

Example 1 Suppose that sulfur reacts with sodium. Sulfur: S -2 Sodium: Na +1 Step 1: Write symbol of cation first, followed by the anion  NaS Step 2: Use subscripts to show the ratio of ions  Na 2 S (sodium sulfide)

Example 2 What is the formula for calcium chloride? Calcium: Ca +2 Chloride: Cl -1 Step 1: Write symbol of cation first, followed by the anion  CaCl Step 2: Use subscripts to show the ratio of ions  CaCl 2

Example 3 What is the formula for calcium oxide? Calcium: Ca +2 Oxide: O -2 Step 1: Write symbol of cation first, followed by the anion  CaO Step 2: Use subscripts to show the ratio of ions  CaO Why: It takes one calcium ion with a charge of + 2 to balance one oxide ion with a charge of - 2.

Prefixes for Naming Compounds 1  Mono 2  Di 3  Tri 4  Tetra 5  Penta

Examples (1) Example 1: N 2 O 4 Dinitrogen tetraoxide Example 2: NO 2 Nitrogen dioxide Note: The prefix “mono” is not used for the first element in the name.

Examples (2) Example 3: P 2 O 5 Answer: diphosphorus pentaoxide Example 4: CO Answer: carbon monoxide

Examples (3) Question: What is the formula for diphosphorus tetrafluoride? Answer: P 2 F 4 Question: What is the formula for dinitrogen monoxide? Answer: N 2 O