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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 or bonds between those particles.
• A substance changes state when enough energy is transferred to overcome the forces between its particles, so substances with stronger forces have higher melting and boiling points.
• The state of a substance at a given temperature can be predicted by comparing the temperature with its melting point and boiling point: below the melting point it is solid, between the melting point and boiling point it is liquid, and above the boiling point it is gas.
• Atoms form positive ions by losing electrons, and atoms form negative ions by gaining electrons.
• Ionic bonding occurs 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 many strong electrostatic forces in the giant ionic lattice require a large amount of energy to overcome.
• Ionic compounds conduct electricity when molten or dissolved in water because their ions are free to move and carry charge.
• Simple molecular substances contain small molecules made from atoms joined by covalent bonds.
• A covalent bond is a shared pair of electrons between two non-metal atoms.
• Simple molecular substances do not conduct electricity because they do not contain free-moving charged particles.
• Intermolecular forces act between simple molecules, and these forces are much weaker than the covalent bonds within the molecules.
• Simple molecular substances have low melting and boiling points because only weak intermolecular forces need to be overcome, not the covalent bonds inside the molecules.
• Giant covalent structures contain many atoms joined by strong covalent bonds in a continuous network.
• Diamond, graphite and silicon dioxide are giant covalent structures with 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 with weak forces between the layers, and it conducts electricity and thermal energy because each carbon atom has one delocalised electron.
• Polymers are large molecules made from repeating units of atoms joined by covalent bonds.
• Graphene is a single layer of carbon atoms arranged in hexagons, while fullerenes are molecules of carbon shaped as hollow cages or tubes, including carbon nanotubes.

• Predict the state of a substance at a specified temperature by comparing the temperature with its melting point and boiling point.
• Draw dot and cross diagrams for ionic compounds by showing electron transfer, ion charges, and full outer shells where appropriate.
• Draw dot and cross diagrams for the covalent bonding in `H_2`, `Cl_2`, `H_2O`, `HCl`, `CH_4`, `O_2`, `N_2` and `NH_3`, showing shared pairs of electrons correctly.
• Represent ionic compounds using correct formulae and diagrams that show the ratio of positive to negative ions needed for overall neutral charge.
• Explain the properties of ionic, simple molecular, giant covalent and metallic substances by linking structure and bonding to melting point, boiling point and electrical conductivity.
• Interpret and draw polymer diagrams by identifying the repeating unit and showing continuation of the chain with bonds extending at both ends.
• Recognise graphene, fullerenes and carbon nanotubes from diagrams and descriptions of their bonding, structure and properties.
• Explain why alloys are harder than pure metals by describing how differently sized atoms distort the layers and make it harder for them to slide.
• Compare nano dimensions with the typical sizes of atoms and molecules, using the idea that nanoparticles are between 1 nm and 100 nm in size.
• Evaluate the use of nanoparticles for a specified purpose by weighing useful properties against possible risks such as toxicity, environmental harm and uncertainty about long-term effects.