WJEC GCSE Chemistry 2.1 Bonding, Structure and Properties Exam Questions

About WJEC GCSE Chemistry 2.1 Bonding, Structure and Properties

Bonding, structure and properties opens Unit 2 of WJEC GCSE Chemistry and explains why substances behave as they do. You need to draw dot and cross diagrams for ionic and covalent bonding, describe metallic bonding, and link the structure of metals, ionic compounds, simple molecular substances and giant covalent structures to their melting points, conductivity and solubility. The forms of carbon, including diamond, graphite, graphene and fullerenes, are covered, along with nanoscience and smart materials. Examiners often ask you to explain properties in terms of bonds or intermolecular forces, and to compare diamond with graphite.

What you need to know

• Ionic bonding Metals lose electrons and non-metals gain them, forming ions with full outer shells; oppositely charged ions attract strongly in a giant lattice. Ionic compounds have high melting points and conduct when molten or dissolved, as the ions can move.
• Covalent bonding Non-metal atoms share pairs of electrons. Simple molecules (e.g. water, carbon dioxide) have low melting and boiling points because only weak forces between molecules must be overcome, and they do not conduct.
• Metallic bonding Metals are a lattice of positive ions in a sea of delocalised electrons. The electrons can move, so metals conduct electricity and heat; layers can slide, so metals are malleable and ductile.
• Forms of carbon Diamond: each carbon bonded to four others, very hard, high melting point, does not conduct. Graphite: layers of carbons each bonded to three others with delocalised electrons, so it conducts and is soft and slippery. Graphene is a single layer of graphite; fullerenes are cage or tube molecules of carbon.
• Nanoscience Nanoparticles are 1 to 100 nm across and have a very large surface area to volume ratio, so they can behave differently from the bulk material. Uses include sun creams, silver nanoparticles in antibacterial products and catalysts; there may be risks to health and the environment.
• Smart materials Their properties change with conditions: thermochromic pigments change colour with temperature, photochromic pigments with light, shape memory alloys return to shape on heating, and hydrogels absorb or release water.

Common mistakes in 2.1 Bonding, Structure and Properties

• Saying simple molecular substances have low melting points because covalent bonds are weak. Covalent bonds are strong; it is the forces between molecules that are weak.
• Writing that ionic solids conduct electricity. The ions are fixed in the lattice; they conduct only when molten or in solution.
• Explaining graphite's conductivity by free ions. Graphite conducts because of delocalised electrons between the layers.
• Forgetting that metallic bonding involves positive ions, not atoms. Describe positive metal ions attracted to a sea of delocalised electrons.

Try three 2.1 Bonding, Structure and Properties exam-style questions