Ions and Ionic Compounds (1)

Chapter 5: Ions and Ionic Compounds

5.5 Ions and Ionic Compounds

• Focus on identifying ions and writing/naming ionic compounds.

Ions

• Atoms are electrically neutral because they contain equal numbers of protons and electrons.

• When electrons are added or removed, atoms become ions:

  • Cation: Positive ion (formed by loss of electrons).

  • Anion: Negative ion (formed by gain of electrons).

Cations

• Formed when atoms lose electrons, leading to an outer shell that is mostly empty.

• Usually formed by metal elements.

Anions

• Formed when atoms gain electrons, occurring when the outer shell is almost full.

• Usually formed by non-metal elements.

• The names of anions typically end with the suffix -ide.

Charges of Representative Elements

• Summary of group ions and their charges:

  • Group 1A: Li+, Na+, K+, etc. (1+ charge)

  • Group 2A: Mg2+, Ca2+, etc. (2+ charge)

  • Group 3A: Al3+

  • Group 5A: N3-, P3-

  • Group 6A: O2-, S2-

  • Group 7A: F-, Cl-, Br-, etc. (1- charge)

Transition Metals and Cations

• Most transition metals and Group 4 metals form multiple positive ions.

• Notable exceptions are Zn2+, Ag+, and Cd2+, which form only one ion.

Naming Ions

• Common ions and their formulas:

  • Cations:

    • Li+ (Lithium)

    • Na+ (Sodium)

    • K+ (Potassium)

    • Mg2+ (Magnesium)

    • Ca2+ (Calcium)

    • Al3+ (Aluminum)

  • Anions:

    • N3- (Nitride)

    • O2- (Oxide)

    • S2- (Sulfide)

    • F- (Fluoride)

    • Cl- (Chloride)

    • Br- (Bromide)

    • I- (Iodide)

Formulas and Names of Ionic Compounds

• Naming Ionic Compounds:

  1. Identify the cation and anion.

  2. Cation is named first, followed by the anion with an –ide ending.

• Examples:

  • NaCl = Sodium Chloride

  • K2S = Potassium Sulfide

  • MgO = Magnesium Oxide

  • CaI2 = Calcium Iodide

  • Al2O3 = Aluminum Oxide

Naming Ionic Compounds with Variable Charge Metals

• When metals can form more than one cation, use Roman numerals to indicate the charge:

  1. Determine charge from anion.

  2. Name cation with its charge in Roman numerals.

  3. Name the anion with an -ide ending.

Examples - Naming with Variable Charge

• FeCl2:

  1. Determine charge: Fe must be Fe2+.

  2. Name: Iron(II) Chloride.

• Cr2O3:

  1. Determine charge: Cr must be Cr3+.

  2. Name: Chromium(III) Oxide.

Writing Formulas from Names

1. Identify cation and anion.

2. Balance the charges to write the formula:

• Example: Potassium Sulfide

  • K+ + S2− → K2S

• Example: Iron(III) Chloride

  • Fe3+ + Cl− → FeCl3

Learning Checks and Solutions

• Identify ionic compounds based on their cations and anions, such as:

  • Sodium (Na+) and Chlorine (Cl−) → NaCl = Sodium Chloride

  • Magnesium (Mg2+) and Oxygen (O2−) → MgO = Magnesium Oxide

• Writing compounds' names and formulas with provided ions:

  • NaBr = Sodium Bromide, Al2S3 = Aluminum Sulfide.