Chemistry | Ionic bonding

👋 Welcome to Ionic Bonding! The Chemistry of Opposites Attract

Hi future chemist! Ionic bonding is one of the fundamental concepts in chemistry, and understanding it is key to explaining why many substances behave the way they do—from the salt you put on your food to the minerals found in rocks.
Don't worry if this seems tricky at first. We will break down this process—which is simply a massive transfer of electrons—into easy, manageable steps. By the end of this chapter, you’ll be able to predict how atoms combine and why table salt melts at an incredibly high temperature!

🔬 Section 1: The Driving Force – Achieving Stability

Every atom in the universe wants to be stable. For most atoms (except Hydrogen and Helium), being stable means having a full outer electron shell.
This state of perfect stability is achieved by the atoms in Group 0 (the Noble Gases), which have 8 electrons in their outer shell (we call this an octet).

The Chemistry Rule of Thumb: The Quest for 8

Atoms that do not have a full outer shell will try to achieve this "magic 8" by either gaining, losing, or sharing electrons. Ionic bonding focuses entirely on the first two methods: gaining and losing electrons.

• Metals (Groups 1, 2, 3) usually have few electrons (1, 2, or 3) in their outer shell. It is easier for them to LOSE these electrons to achieve the full shell underneath.
• Non-metals (Groups 5, 6, 7) usually have many electrons (5, 6, or 7) in their outer shell. It is easier for them to GAIN electrons to complete the shell.

⚡ Section 2: Forming Charged Particles – Ions

When an atom gains or loses electrons, its number of protons (positive charges) no longer equals its number of electrons (negative charges). This results in a charged particle called an ion.

How Metals Form Positive Ions (Cations)

When a metal atom loses electrons, it loses negative charge. Since the number of positive protons remains the same, the resulting particle has a net positive charge.

• Group 1 metals lose 1 electron → form a +1 ion (e.g., \(Na^+\)).
• Group 2 metals lose 2 electrons → form a +2 ion (e.g., \(Mg^{2+}\)).

How Non-metals Form Negative Ions (Anions)

When a non-metal atom gains electrons, it gains negative charge. Since the number of positive protons remains the same, the resulting particle has a net negative charge.

• Group 7 non-metals gain 1 electron → form a -1 ion (e.g., \(Cl^-\)).
• Group 6 non-metals gain 2 electrons → form a -2 ion (e.g., \(O^{2-}\)).

⚛️ Section 3: The Ionic Bond Explained

An Ionic Bond is the strong electrical force of attraction between oppositely charged ions (a positive metal ion and a negative non-metal ion).

The Process of Ionic Bonding (The Handshake)

1. The metal atom gives away its outer electrons. It becomes a positively charged Cation.
2. The non-metal atom takes these electrons. It becomes a negatively charged Anion.
3. Once they are charged, the strong Electrostatic Forces of Attraction pull the positive and negative ions together, holding them tightly in a fixed structure.

Analogy: Think of two magnets. One is positive, one is negative. If you push them close together, they snap together tightly and are very hard to pull apart. This strong attraction is the ionic bond!

✏️ Section 4: Drawing Ionic Compounds (Dot and Cross Diagrams)

Dot and Cross diagrams are how we visualize the transfer of electrons and the resulting full outer shells of the ions.

Step-by-Step Example: Sodium Chloride (NaCl)

Sodium (Na, Group 1) has 1 outer electron (use dots). Chlorine (Cl, Group 7) has 7 outer electrons (use crosses).

1. Start Atoms: Draw Na with 1 electron and Cl with 7 electrons.
2. Transfer: The single electron from Na is moved completely to the Cl atom.
3. Resulting Ions:
   • Na has lost its outer shell. We draw the remaining full shell inside square brackets, showing 0 outer electrons (but remember the shell underneath is full!). The charge is written outside: \([Na]^+\).
   • Cl now has 8 electrons (7 crosses + 1 dot from Na). We draw the full outer shell inside square brackets. The charge is written outside: \([Cl]^-\).

Example 2: Magnesium Chloride (MgCl₂)

Magnesium (Mg, Group 2) needs to lose 2 electrons. Chlorine (Cl, Group 7) needs to gain 1 electron.

To balance the charges (and achieve stability for all atoms), one Mg atom must bond with two Cl atoms. Mg gives one electron to the first Cl, and the second electron to the second Cl.

The resulting structure shows:
\( [Mg]^{2+} \text{ and } 2 \times [Cl]^- \)

🧱 Section 5: Structure and Properties of Ionic Compounds

Ionic compounds do not exist as simple molecules (like \(H_2O\)). Instead, they form a massive, repeating pattern known as a Giant Ionic Lattice.

• Positive and negative ions are packed together tightly in an orderly, three-dimensional arrangement.
• Every positive ion is surrounded by negative ions, and vice versa.
• This structure is held together by the very strong electrostatic forces of attraction.

Properties Derived from the Giant Ionic Lattice

1. High Melting and Boiling Points

Because the electrostatic forces holding the ions together are extremely strong, it takes a huge amount of energy to overcome them. Therefore, ionic compounds have very high melting points (M.P.) and boiling points (B.P.).
Example: Table salt (NaCl) melts at over 800 °C.

2. Electrical Conductivity

For a substance to conduct electricity, it must contain mobile charged particles (particles that are free to move).

• Solid State: Ionic solids DO NOT conduct electricity. Why? Because the ions are locked firmly in fixed positions within the lattice and cannot move to carry the current.
• Molten (Liquid) State or Aqueous (Dissolved) State: Ionic compounds DO conduct electricity. Why? When melted or dissolved in water, the strong lattice breaks down, and the ions are now free to move and carry the electrical current.

3. Solubility

Many ionic compounds are soluble in water. This is because water molecules are polar and can attract the positive and negative ions, pulling them out of the strong lattice structure.

Did You Know? Many essential mineral nutrients required by your body, such as calcium, potassium, and magnesium, are transported and used in the body in the form of dissolved ions!