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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.
• Substances change state at different temperatures because different substances have different strengths of forces or bonds between their particles.
• The particle model represents particles as small spheres, so it does not show particle size, shape, forces, bonds, or the space inside atoms.
• Atoms form positive ions by losing electrons, and atoms form negative ions by gaining electrons.
• Ionic bonding is the strong electrostatic attraction between oppositely charged ions.
• An ionic compound is made from positive ions and negative ions in fixed ratios so that the overall charge is zero.
• A giant ionic lattice is a regular three-dimensional arrangement of many oppositely charged ions held together by strong electrostatic forces.
• 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.
• Covalent bonding is the sharing of pairs of electrons between non-metal atoms.
• Simple molecular substances have low melting and boiling points because the intermolecular forces between molecules are weak, even though the covalent bonds inside each molecule are strong.
• 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 strong covalent bonds between atoms.
• Giant covalent substances have high melting and boiling points because many strong covalent bonds must be broken.
• In diamond, each carbon atom forms four covalent bonds in a rigid giant covalent structure, making diamond very hard.
• In graphite, each carbon atom forms three covalent bonds in layers, with weak forces between layers and delocalised electrons that allow graphite to be soft, slippery, and electrically conductive.
• Polymers are very large molecules made from many atoms joined by covalent bonds in long chains.
• Metals have giant metallic structures made of positive metal ions in a regular arrangement surrounded by delocalised electrons.
• Metallic bonding is the strong electrostatic attraction between positive metal ions and delocalised electrons, which explains why metals conduct electricity and thermal energy, are malleable, and often have high melting points.

• 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 by showing electron transfer, correct ion charges, and full outer shells where appropriate.
• Interpret the formula of an ionic compound by identifying the number and type of ions present from the symbols and subscripts.
• Generate the formula of an ionic compound from ion charges by choosing the simplest ratio of ions that gives zero overall charge.
• Draw dot and cross diagrams for simple covalent molecules, including hydrogen, chlorine, water, hydrogen chloride, methane, oxygen, nitrogen and ammonia, showing shared pairs and outer-shell electrons.
• Explain physical properties of substances by linking structure and bonding to forces between particles, mobile charged particles, and the energy needed to overcome attractions.
• Compare the limitations of dot and cross diagrams, ball-and-stick models, two-dimensional diagrams and three-dimensional models by stating what each model shows and what it leaves out.
• Justify uses of diamond, graphite, graphene, fullerenes, carbon nanotubes, metals and alloys by linking their structure to their properties.
• Interpret and draw polymer diagrams by identifying the repeating unit and showing how atoms are joined in a long covalent chain.
• Evaluate the use of nanoparticles for a specific purpose by comparing benefits with possible risks, including their very small size, large surface area to volume ratio, and uncertain effects on health or the environment.