2.4 Ions and Ionic Bonds

2026 Syllabus Objectives

  1. Core: Describe the formation of positive ions, known as cations, and negative ions, known as anions
  2. Core: State that an ionic bond is a strong electrostatic attraction between oppositely charged ions
  3. Core: Describe the formation of ionic bonds between elements from Group I and Group VII, including the use of dot-and-cross diagrams
  4. Core: Describe the properties of ionic compounds:
    • (a) high melting points and boiling points
    • (b) good electrical conductivity when aqueous or molten and poor when solid
  5. Supplement: Describe the giant lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions
  6. Supplement: Describe the formation of ionic bonds between ions of metallic and non-metallic elements, including the use of dot-and-cross diagrams
  7. Supplement: Explain in terms of structure and bonding the properties of ionic compounds:
    • (a) high melting points and boiling points
    • (b) good electrical conductivity when aqueous or molten and poor when solid

What is Ionic Bonding? ⚡

https://cambridgeassistant.com

Two major types of bonds hold compounds together. The first is covalent bonding, which involves the sharing of electrons, usually between atoms of non-metals. However, compounds between metals and non-metals involve a second type of bonding known as ionic bonding.

In ionic bonding, electrons are transferred from one atom to another, forming ions. These ionic compounds are held together by electrostatic forces of attraction between the oppositely charged ions.

Key Definitions 🔑

Ionic bonding: A strong electrostatic force of attraction between oppositely charged ions.

Ions: Charged particles made from an atom, or groups of atoms (compound ions), by the loss or gain of electrons.

Electrostatic forces: Strong forces of attraction between particles with opposite charges - such forces are involved in ionic bonding.

Cation: A positive ion that would be attracted to the cathode in electrolysis.

Anion: A negative ion that would be attracted to the anode in electrolysis.

Formation of Ions 📌

https://cambridgeassistant.com

An ion is an electrically charged particle. Ions are formed when atoms lose or gain electrons to achieve a stable electron configuration.

Noble gas atoms (except helium) have eight electrons in their outer shells. Most atoms do not have this arrangement and are more reactive. One way of gaining this noble gas structure is to completely transfer electrons from one atom to another.

Formation of Cations (Positive Ions)

Metals in Group I all have one electron in their outer energy level. By losing this electron, they achieve a stable noble gas configuration.

Example: Formation of a Sodium Ion

A sodium atom has 11 protons and 11 electrons with electron arrangement [2,8,1][2,8,1]. By losing the single outer electron, it forms a Na+\mathrm{Na}^{+} ion with 10 electrons and electron arrangement [2,8][2,8].

The sodium ion now has a single positive charge because there are 11 protons but only 10 electrons.

Na [2,8,1]⟶Na+ [2,8]+e−\mathrm{Na} \, [2,8,1] \longrightarrow \mathrm{Na}^{+} \, [2,8] + e^{-}

Important: The sodium ion (Na+\mathrm{Na}^{+}) now has the stable electron arrangement [2,8][2,8] of a neon atom.

Formation of Anions (Negative Ions)

Halogen atoms in Group VII have seven outer electrons. They can achieve a stable noble gas configuration by gaining one outer electron.

Example: Formation of a Chloride Ion

A chlorine atom has 17 protons and 17 electrons with electron arrangement [2,8,7][2,8,7]. By gaining one electron, it forms a Cl−\mathrm{Cl}^{-} ion with 18 electrons and electron arrangement [2,8,8][2,8,8].

The chloride ion now has a single negative charge because there are 17 protons but 18 electrons.

Cl [2,8,7]+e−⟶Cl− [2,8,8]\mathrm{Cl} \, [2,8,7] + e^{-} \longrightarrow \mathrm{Cl}^{-} \, [2,8,8]

Important: The chloride ion (Cl−\mathrm{Cl}^{-}) now has the stable electron arrangement [2,8,8][2,8,8] of an argon atom.

Predicting Ion Charges from Group Number

  • Group I elements form ions with a 1+ charge (e.g., Na+\mathrm{Na}^{+}, Li+\mathrm{Li}^{+})
  • Group II elements form ions with a 2+ charge (e.g., Mg2+\mathrm{Mg}^{2+}, Ca2+\mathrm{Ca}^{2+})
  • Group VI elements form ions with a 2- charge (e.g., O2−\mathrm{O}^{2-})
  • Group VII elements form ions with a 1- charge (e.g., Cl−\mathrm{Cl}^{-}, F−\mathrm{F}^{-})

Sign in to view full notes