2.1 - Chemical Bonds (Ionic, Covalent, Metallic)

What is ionic bonding?

What is ionic bonding?

The electrostatic attraction between positive and negative ions. It’s a relatively strong attraction.

How are ionic compounds held together?

• They are held together in a giant lattice.

• It’s a regular structure that extends in all directions in a substance.

• Electrostatic attraction between positive and negative ions holds the structure together.

State the properties of ionic substances.

• High melting and boiling point (strong electrostatic forces between oppositely charged ions).

• Don’t conduct electricity when solid (ions in fixed positions).

• Conduct when molten or dissolved in water - ions are free to move.

Give 5 examples of positive ions and 5 examples of negative ions.

• Positive: Na⁺, Mg²⁺, Al³⁺, Ca²⁺, Rb⁺

• Negative: Cl^-, Br^-, SO₄^2-, NO₃^-, OH^- (chloride, bromide, sulfate, nitrate, hydroxide).

What is important when working out a formula of an ionic compound?

Ionic compounds are electrically neutral, e.g. positive and negative charges balance each other.

How are ionic compounds formed? Explain in terms of MgO case?

• Reaction of a metal with a non-metal.

• Electron transfer occurs - metal gives away its outer shell electrons to non-metal.

• Mg is in Group 2 so has 2 available outer shell electrons, while O is in Group 6. so can accept 2 electrons to get a full outer shell configuration.

• Mg becomes Mg²⁺ and O^2- becomes O (oxide).

What is a covalent bond?

A shared pair of electrons between two atoms.

Describe the structure and properties of simple molecular covalent substances.

• Don’t conduct electricity (no ions).

• Small molecules.

• Weak intermolecular forces, therefore:

• Low melting and boiling points.

What is metallic bonding?

Forces of attraction between delocalized electrons and nuclei of metal ions.

How do metallic bonds form?

• Metals consist of giant structures of atoms arranged in a regular pattern.

• The electrons in the outer shell of metal atoms are delocalized and so are free to move through the whole structure.

• The sharing of delocalized electrons gives rise to strong metallic bonds.