(1f) Ionic Bonding

Formation of Ions

• electrically charged atom or group of atoms formed by the loss or gain of electrons

• takes place to obtain a full outer shell of electrons

Metal Ions

lose electrons to become positively charged

Non-Metal Ions

gain electrons from other atoms to become negatively charged

Formation of Cations

Formation of Anions

Finding Ion Charge

• find outer shell electron numbers

• is it easier to gain or lose?

  • >4: receive electrons

  • <4: donate electrons

• type of ion formed:

  • gain electrons: anion

  • lose electrons: cation

Ammonium Ion

NH₄⁺

Hydroxide Ion

OH^-

Carbonate Ion

CO₃^2-

Nitrate Ion

NO₃^-

Sulfate Ion

SO₄^2-

Group 1 Ions

Metals: 1+ (Na⁺)

Group 2 Ions

Metals: 2+ (Mg²⁺)

Group 3 Ions

Metals: 3+ (Al³⁺)

Group 5

Non-metals: 3- (N^3-)

Group 6

Non-metals: 2- (O^2-)

Group 7

Non-metals: 1- (Cl^-)

Ionic compounds have no overall charge because:

Size of any positively charged ions is cancelled by the size of the negatively charged ion

Forming Ionic Compounds (Direct Comparison)

Formula can be determined by directly comparing charges of the ions

• Metal charge (ex:2+)

• Non-metal charge (ex:2-)

• Charges cancel out [ (2+) + (2-) = 0 ]

• means one non-metal ion is needed to cancel out one metal ion

Dot and Cross Diagrams

• electrons from each atom should be diagrammatically dots and crosses

• put one atom’s electrons in dots and the other in crosses

• >2 atoms: hollow circles or other symbols may be used

• transfer dots from one atom to the other to show electron donated

• shells filled = atoms become ions

• large square brackets should encompass each ion

• charge in superscript on right hand side outside bracket

• put number on left hand side to show ratio

Ionic Bonding

• ionic compounds: regular arrangement of alternating positive and negative ions where ions are tightly packed together

• between cations and anions there are strong electrostatic forces of attraction in all directions

Ionic Lattices

• thousands of cations and anions in an ionic compound form a giant lattice structure

• giant lattice compounds have high melting points

Ionic compounds have high melting and boiling points because:

• giant ionic lattices

• strong electrostatic forces of attraction between oppositely charged ions in all directions

• forces need lots of energy to overcome them

  • greater charge = greater attractive forces

  • higher melting point

  • ex: MgO (Mg²⁺ and O^2-) has a higher melting point than NaCl (Na⁺ and Cl^-)

Conductivity of Ionic Compounds

• for electrical current to flow there must be freely moving charged particles like electrons or ions present

• ionic compounds are poor conductors as solids

  • ions are in fixed position in lattice

  • so they are unable to move and carry a charge

• good conductors as molten or in solution

  • melted or dissolved = ions can move and carry a charge