Chapter 3 Ionic Compounds Notes

Introduction to Bonding

  • Bonding is the joining of two atoms in a stable arrangement.
  • Elements gain, lose, or share electrons to achieve the electron configuration of the nearest noble gas.
  • Ionic bonds: Transfer of electrons.
  • Covalent bonds: Sharing of electrons.
  • Ionic bonds usually form between a metal and a nonmetal.
  • Covalent bonds form when two nonmetals combine or when a metalloid bonds to a nonmetal.
  • A molecule contains two or more atoms joined by covalent bonds.

Ionic Compounds

  • Composed of metal cations and nonmetal anions.
  • Metal cations are positively charged ions.
  • Nonmetal anions are negatively charged ions.
  • Cations and anions exist in proportions that yield electrical neutrality.
  • Ions are arranged in a crystal lattice.
  • Also called salts.

Ions

  • Ions are charged species with unequal numbers of protons and electrons.
  • Ionic compounds have strong electrostatic attraction between oppositely charged ions.
  • Cations are positively charged with fewer electrons than protons.
  • Anions are negatively charged with more electrons than protons.
  • Metals form cations by losing electrons to achieve a filled outer shell.
  • Nonmetals form anions by gaining electrons to achieve a filled outer shell.
  • The octet rule states that main group elements are stable with eight valence electrons.

Relating Group Number to Ionic Charge

  • Elements in the same group form ions of similar charge.
  • For metals in groups 1A, 2A, and 3A: group number = cation charge.
  • For nonmetals in groups 6A and 7A: anion charge = 8 − group number.

Metals with Variable Charge

  • Roman numerals indicate the charge on the cation.

Ionic Compounds Formula

  • Ionic bond forms when a metal transfers electrons to a nonmetal.
  • The overall charge in an ionic compound must be zero.
How to Write a Formula for an Ionic Compound
  • Step 1: Identify the cation and anion.
  • Step 2: Determine the number of each ion needed for a charge of zero.
  • Step 3: Write the formula with the cation first, then the anion, omitting charges and using subscripts to indicate the number of ions.

Naming Ionic Compounds

  • Cations are named for the element from which they are formed.
  • For metals with two different cations, use:
    • Systematic name: Element name followed by Roman numeral indicating charge.
Naming Anions
  • Anions are named by replacing the ending of the element name with the suffix “-ide.”
Naming Ionic Compounds Steps
  • Name the cation first, then the anion.
Naming Ionic Compounds with Variable Charge Steps
  • Step 1: Determine the charge on the cation.
  • Step 2: Name the cation and the anion.
  • Step 3: Write the name of the cation first, then the anion.
Deriving a Formula from the Name Steps
  • Step 1: Identify the cation and anion and determine their charges.
  • Step 2: Balance charges.
  • Step 3: Write the formula, with the cation first, and use subscripts to show how many of each ion is needed to have zero overall charge.

Physical Properties of Ionic Compounds

  • Ionic compounds are crystalline solids with high melting and boiling points.
  • When dissolved in water, they separate into ions, increasing conductivity.

Polyatomic Ions

  • Polyatomic ions are ions that contain more than one atom.
  • Writing formulas is the same as with single-atom ions.
  • When a cation and anion of equal charge combine, only one of each ion is needed.
  • When a cation and anion of unequal charge combine, use the ionic charges to determine the number of each ion needed.