1.3. Ionic bonding

Edexcel GCSE Chemistry: Key Concepts in Chemistry

1. Ionic Bonding

• Ionic bonds are formed by the transfer of electrons between atoms, producing cations (positively charged ions) and anions (negatively charged ions).

• Metals and Nonmetals:

  • Metals lose electrons from their outer shell to become cations.

  • Nonmetals gain electrons to become anions.

• Dot and Cross Diagrams:

  • Electron transfer can be illustrated using dot and cross diagrams, exemplified by the formation of NaCl (sodium chloride).

2. Definition of Ion

• An ion is defined as an atom or group of atoms that possesses a positive or negative charge.

• Formation of ions:

  • Metal atoms lose electrons to become positively charged ions.

  • Non-metal atoms gain electrons to become negatively charged ions.

3. Calculating Protons, Neutrons, and Electrons in Ions

• Atomic Number: Indicates the number of protons.

• Mass Number: Sum of protons and neutrons.

• In neutral atoms, the number of protons equals the number of electrons, but this changes in ions:

  • To determine the number of electrons:

    • Start with the number of protons (atomic number).

    • Add or subtract electrons based on the ion's charge (-ve for gained electrons, +ve for lost electrons).

4. Ion Formation in Ionic Compounds by Groups 1, 2, 6, and 7

• Ions formed by metals in Groups 1 and 2 and nonmetals in Groups 6 and 7 have noble gas electronic structure:

  • Group 1 metals lose 1 electron to form +1 ions.

  • Group 2 metals lose 2 electrons to form +2 ions.

  • Group 6 nonmetals gain 2 electrons to form 2- ions.

  • Group 7 nonmetals gain 1 electron to form 1- ions.

• Charge Balance: The overall charge of the compound must be zero, requiring balance between positive and negative charges.

5. Naming Compounds with -ide and -ate Suffixes

• The suffixes indicate the type of negatively charged ions in a compound:

  • -ide: Compounds with two elements (including one nonmetal anion).

  • -ate: Compounds with at least three elements, one of which is oxygen.

6. Formulae of Ionic Compounds

• Common anions and their associated formulas:

  • Oxides: O2- (e.g., Sodium Oxide: Na2O)

  • Hydroxides: OH1- (e.g., Sodium Hydroxide: NaOH)

  • Halides: -1 halide ion (e.g., Sodium Chloride: NaCl)

  • Nitrates: NO3 1- (e.g., Sodium Nitrate: NaNO3)

  • Carbonates: CO3 2- (e.g., Sodium Carbonate: NaCO3)

  • Sulfates: SO4 2- (e.g., Sodium Sulfate: NaSO4)

• To deduce compound formulae, balance the positive and negative charges by using subscripts (e.g., Cl3, or (SO4)2).

7. Structure of Ionic Compounds

• Ionic compounds form a lattice structure:

  • Consists of a regular arrangement of ions.

  • Held together by strong electrostatic forces (ionic bonds) between oppositely charged ions.

  • Forces act in all directions, contributing to the stability and rigidity of the lattice.

  • Example: Sodium Chloride (NaCl) demonstrates a lattice structure with Na+ (smaller) and Cl- (larger) ions.