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neurologyYou need to know

• Melting point and boiling point depend on the type of particles in a substance and the strength of the forces between those particles.
• Substances change state at different temperatures because different substances have different types and strengths of bonding or intermolecular forces.
• The particle model represents substances as particles arranged differently in solids, liquids and gases, but it does not show particle size, forces between particles, or the differences between atoms, ions and molecules.
• Atoms form positive ions when they lose electrons, and atoms form negative ions when they gain electrons.
• Ionic bonding happens when electrons are transferred from metal atoms to non-metal atoms, forming oppositely charged ions.
• Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions.
• A giant ionic lattice is a regular three-dimensional arrangement of many positive and negative ions held together by ionic bonds in all directions.
• Ionic compounds have high melting points because a large amount of energy is needed to overcome the strong electrostatic forces in the giant ionic lattice.
• Solid ionic compounds do not conduct electricity because their ions are fixed in position and cannot move to carry charge.
• Molten ionic compounds and ionic compounds dissolved in water conduct electricity because their ions are free to move and carry charge.
• The formula of an ionic compound shows the ratio of positive ions to negative ions needed to balance the total charge to zero.
• Simple molecular substances contain small molecules with covalent bonds between atoms.
• A covalent bond is a shared pair of electrons between two non-metal atoms.
• Double covalent bonds contain two shared pairs of electrons, and triple covalent bonds contain three shared pairs of electrons.
• Simple molecular substances have low melting and boiling points because the intermolecular forces between molecules are weak compared with covalent bonds.
• Simple molecular substances do not conduct electricity because they do not contain mobile charged particles.
• Diamond, graphite and silicon dioxide are giant covalent structures with many atoms joined by strong covalent bonds.
• Giant covalent substances have high melting and boiling points because many strong covalent bonds must be broken.
• Diamond is hard because each carbon atom forms four strong covalent bonds in a rigid three-dimensional giant covalent structure.
• Graphite is soft and slippery because it has layers of carbon atoms that can slide over each other, and it conducts electricity and thermal energy because it has delocalised electrons.

• Predict the state of a substance at a given temperature by comparing the temperature with its melting point and boiling point.
• Draw dot and cross diagrams for ionic compounds, showing electron transfer, full outer shells and the correct charges on the ions.
• Interpret ionic formulae by identifying the type and number of each ion present in the compound.
• Generate the formula of an ionic compound from given ion charges by balancing the total positive and negative charge to zero.
• Explain the physical properties of ionic compounds using the giant ionic lattice model, including melting point and electrical conductivity.
• Draw dot and cross diagrams for simple covalent molecules including hydrogen, chlorine, water, hydrogen chloride, methane, oxygen, nitrogen and ammonia.
• Evaluate models of bonding and structure, including dot and cross, ball and stick, two-dimensional and three-dimensional models, by identifying what each model shows and what it leaves out.
• Interpret and draw polymer diagrams by identifying the repeating unit and showing covalent bonds between atoms in the chain.
• Recognise graphene, fullerenes and carbon nanotubes from diagrams and descriptions of their bonding and structure.
• Explain the properties of metals and alloys using metallic bonding, delocalised electrons, layers of atoms and disruption of layers by differently sized atoms.