Chemistry IGCSE Revision Already Graded A+

Chemistry IGCSE Revision Already Graded A+ Ionic Bonding ️Between a metal and a non-metal 1) soluble in water - polar water molecules are attracted to the giant 3D crystal lattice and break it apart 2) conduct electricity when molten - when molten, the bonds have broken and the electrons are free to move and carry charge 3) normally solids at room temperature - ions held in a fixed position by strong bonds 4) higher melting and boiling points - strong ionic bonds in a 3D crystal lattice that take much energy to break Covalent Bonding ️Between 2 non-metals 1) insoluble in water 2) brittle solids, liquids or gases at room temperature 3) don't conduct electricity when molten 4) lower melting and boiling points - molecules are held together by weak intermolecular forces that are easy to break Diatomic Gases: a nitrogen molecule has a triple bond, a carbon dioxide molecule has two double bonds, an oxygen molecule has two double bonds. Cation ️Positive Ion Anion ️Negative Ion Metallic Bonding ️An array of positive ions in a sea of delocalised electrons. Most metals are hard and have high melting points. Good conductors of heat. Malleable and ductile. Solids ️Particles are closely packed in a regular structure. The only movement the particles have is vibration. Liquid ️Particles are still mainly touching but some gaps have appeared. Liquids are usually less dense that the solid. Gas ️Particles are much further apart and there are almost no forces of attraction between them. Changes of State ️Solid --> Liquid - Melting Liquid --> Solid - Freezing Liquid --> Gas - Boiling Gas --> Liquid - Condensing Solid --> Gas and Gas --> Solid - Sublimation Diffusion ️The spreading out of particles in a gas or a liquid. The lighter the particles, the faster they diffuse. This is demonstrated by the experiment with cotton wool soaked in ammonia solution at one end of a tube and cotton wool soaked in HCl at the other end. The white cloud of ammonium chloride forms closer to the hydrochloric end. Also to speed up diffusion, you can stir a liquid or heat up the liquid or gas. Isotope ️Atoms that have the same atomic number but different mass numbers. They have the same number of protons but a different number of neutrons. Number of electrons = number of protons. Alloys ️An alloy is a mixture of metals, e.g. brass is a mixture of copper and zinc. In an alloy, the different metals have slightly differently sized atoms. This breaks up the regular arrangement and makes it more difficult for the layers to slide. Giant Ionic Structures ️All ionic compounds are huge lattices which is a regular array of particles. e.g. sodium chloride Giant Covalent Structures ️Diamond - 4 strong bonds so very high melting and boiling points. Cannot conduct electricity because no free ions to move and carry charge. Insoluble. Silican dioxide has similar properties to diamond. Carbon - 3 strong bonds but 4 ions so there's a free one to move and carry charge so carbon can conduct electricity. Good lubricant as carbon is made up in sheets which can slide over each other. Valencies ️Sulph and Carb are 2, phos is 3, everything else is 1. Zinc and Mercury have valencies of 2 and Silver has a valency of 1. Acids and Alkalis ️All acids contain H, all alkalis contain OH. Rates of Reaction ️To speed up the reaction you can: 1) increase the surface area (but use same quantities) 2) increase the temperature - increases kinetic energy of particles so more likely t