Ionic, Covalent & Metallic Bonding and Properties
Chemical bonding explains how atoms achieve stable full outer electron shells: metals react with non-metals by transferring electrons (ionic bonding), non-metals react with non-metals by sharing pairs of electrons (covalent bonding), and metals bond via a sea of delocalised electrons (metallic bonding). The physical properties of any substance, including its melting point, malleability, and electrical conductivity, depend directly on the type of particles present and the strength of the forces between them. Examiners frequently penalise students who confuse breaking weak intermolecular forces in simple covalent molecules with breaking strong covalent bonds.
- Ionic Bonding & Electron Transfer
- Occurs between metals and non-metals. Metal atoms lose outer-shell electrons to form positively charged ions (cations), and non-metal atoms gain those electrons to form negatively charged ions (anions), both achieving the stable electronic structure of a noble gas.
- Giant ionic lattice properties
- Ionic compounds (e.g., NaCl, MgO) form regular 3D giant ionic lattices held together by strong electrostatic forces of attraction between oppositely charged ions acting in all directions. They have high melting/boiling points (lots of energy needed to overcome strong electrostatic forces) and conduct electricity only when molten or aqueous (when ions are mobile).
- Covalent Bonding & Shared Electron Pairs
- Occurs between non-metal atoms, which share pairs of outer-shell electrons to achieve full outer shells. A single bond is 1 shared pair of electrons (e.g., H₂, Cl₂, HCl, H₂O, CH₄, NH₃), a double bond is 2 shared pairs (O₂, CO₂), and a triple bond is 3 shared pairs (N₂).
Ionic, Covalent & Metallic Bonding and Properties: 3D Molecular, Lattice, DNA & Vector Explorer
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Giant Ionic Lattice (Sodium Chloride, NaCl)
- Bonding Type:
- Strong electrostatic attraction between oppositely charged Na⁺ and Cl⁻ ions in all directions
- Melting / Sublimation Point:
- High (801°C): large energy needed to overcome many strong electrostatic attractions
- Electrical Conductivity:
- Insulator when solid (ions fixed in lattice); conducts when molten or aqueous (mobile ions carry charge)
Never write 'delocalised electrons' for an ionic compound. Solid NaCl does not conduct because its ions are locked in fixed positions; melting or dissolving frees the ions to move.
Key Concepts & Exam Definitions (6)
- Ionic Bonding & Electron Transfer
- Occurs between metals and non-metals. Metal atoms lose outer-shell electrons to form positively charged ions (cations), and non-metal atoms gain those electrons to form negatively charged ions (anions), both achieving the stable electronic structure of a noble gas.
- Giant ionic lattice properties
- Ionic compounds (e.g., NaCl, MgO) form regular 3D giant ionic lattices held together by strong electrostatic forces of attraction between oppositely charged ions acting in all directions. They have high melting/boiling points (lots of energy needed to overcome strong electrostatic forces) and conduct electricity only when molten or aqueous (when ions are mobile).
- Covalent Bonding & Shared Electron Pairs
- Occurs between non-metal atoms, which share pairs of outer-shell electrons to achieve full outer shells. A single bond is 1 shared pair of electrons (e.g., H₂, Cl₂, HCl, H₂O, CH₄, NH₃), a double bond is 2 shared pairs (O₂, CO₂), and a triple bond is 3 shared pairs (N₂).
- Simple Molecular Substances & Intermolecular Forces
- Substances made of small covalent molecules have strong covalent bonds between atoms within each molecule, but only weak intermolecular forces between separate molecules. They have low melting/boiling points because little energy is needed to overcome the weak intermolecular forces, and they do not conduct electricity because molecules have no overall electric charge and no free electrons.
- Polymer Chains & Molecular Size
- Polymers are very large molecules made of repeating monomer units joined by strong covalent bonds. Because polymer molecules are much larger than simple molecules, the intermolecular forces between polymer chains are cumulatively much stronger, meaning more energy is needed to overcome them, so polymers are solids at room temperature.
- Metallic Bonding & Delocalised Electrons
- Metals consist of a giant structure of positive metal ions arranged in regular layers, surrounded by a sea of delocalised outer-shell electrons. Strong electrostatic attraction between the positive metal ions and negative delocalised electrons gives metals high melting points. Delocalised electrons move freely to conduct electricity and thermal energy.
Quick-Fire Flashcards (6)
Click any card to check the answer, then mark it as Known to track your progress.
Describe the electron transfer when magnesium reacts with oxygen to form magnesium oxide (MgO).
Why does magnesium oxide (MgO) have a much higher melting point than sodium chloride (NaCl)?
Explain why chlorine (Cl₂) is a gas at room temperature.
Why does the boiling point of the Group 7 halogens (or alkanes) increase as relative molecular mass increases?
Beware the exam trap: Do ions or electrons carry the charge in a molten ionic compound vs a solid metal?
Why are alloys harder than pure metals?
Exam-Style Questions & Mark Schemes (4)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Describe what happens to the electrons when potassium reacts with chlorine to form potassium chloride, and explain why potassium chloride has a high melting point. [5 marks]
Click “Check Mark Scheme” to compare your answer, 1. A potassium atom (Group 1) loses 1 outer-shell electron to form a positively charged potassium ion, K⁺ [1 mark]. 2. A chlorine atom (Group 7) gains that 1 electron into its outer shell to form a negatively charged chloride ion, Cl⁻ (giving both ions stable full outer shells) [1 mark]. 3. Potassium chloride forms a giant ionic lattice structure [1 mark]. 4. There are strong electrostatic forces of attraction between the oppositely charged K⁺ and Cl⁻ ions acting in all directions [1 mark]. 5. A large amount of thermal energy is needed to overcome these strong electrostatic forces, resulting in a high melting point [1 mark].
- Q2
Explain why solid sodium chloride does not conduct electricity, whereas molten sodium chloride and solid copper both conduct electricity well. [4 marks]
Click “Check Mark Scheme” to compare your answer, 1. In solid sodium chloride, the Na⁺ and Cl⁻ ions are held in fixed positions within the giant ionic lattice and cannot move to carry charge [1 mark]. 2. When sodium chloride is melted (molten), the lattice breaks down and the charged ions become free to move and carry electrical charge [1 mark]. 3. Solid copper has metallic bonding, consisting of positive copper ions surrounded by a sea of delocalised electrons [1 mark]. 4. These delocalised electrons are free to move throughout the solid metal structure and carry electrical charge [1 mark].
- Q3
Ammonia (NH₃) has a melting point of -78°C and does not conduct electricity. Explain these two properties in terms of its structure and bonding. [4 marks]
Click “Check Mark Scheme” to compare your answer, 1. Ammonia has a simple molecular structure (consists of small covalent molecules) [1 mark]. 2. There are only weak intermolecular forces of attraction between the NH₃ molecules [1 mark]. 3. Very little energy is required to overcome these weak intermolecular forces, so ammonia has a very low melting point [1 mark]. 4. Ammonia does not conduct electricity because the covalent molecules have no overall electric charge and there are no free/delocalised electrons or mobile ions [1 mark].
- Q4
Explain why pure copper can be bent easily into shapes and used for electrical wiring. [4 marks]
Click “Check Mark Scheme” to compare your answer, 1. Copper consists of a giant lattice of positive metal ions arranged in regular layers, surrounded by delocalised electrons [1 mark]. 2. In pure copper, all the metal atoms/ions are the same size, so the regular layers of ions can slide over each other easily when a force is applied (making it malleable/ductile) [1 mark]. 3. The outer-shell electrons in copper are delocalised [1 mark]. 4. These delocalised electrons are free to move through the metal and carry electrical charge [1 mark].
Common Exam Questions (4)
Why do ionic compounds conduct electricity only when molten or dissolved in water?
In a solid giant ionic lattice, the positive and negative ions are held in fixed positions by strong electrostatic forces and cannot move. When melted (molten) or dissolved in water (aqueous), the lattice breaks down and the ions are free to move and carry charge through the liquid.
What is the most common mistake students make when explaining the low boiling point of simple covalent molecules?
Never say that covalent bonds break when water or carbon dioxide boils. Covalent bonds inside the molecules are very strong and do not break during state changes. Instead, state that weak intermolecular forces between the molecules require very little thermal energy to overcome.
Why are pure metals malleable and good conductors of electricity?
Metals consist of a regular giant lattice of positive metal ions surrounded by a 'sea' of delocalised outer-shell electrons. They are malleable because the regular layers of identically sized positive ions can slide over one another easily without shattering, and they conduct electricity because the delocalised electrons are free to move through the structure and carry charge.
How do you determine the charges on ions from their Group number in the Periodic Table?
Group 1 metals lose 1 outer electron to form +1 ions (e.g., Na⁺). Group 2 metals lose 2 electrons to form +2 ions (Mg²⁺). Group 6 non-metals gain 2 electrons to form -2 ions (O²⁻). Group 7 halogens gain 1 electron to form -1 ions (Cl⁻).
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