Chemistry

• Isotopes are atoms of the same element with the same number of protons (atomic number) but different numbers of neutrons ( mass number)
• The atomic number is equal to the number of protons
• A molecule is two or more atoms chemically bonded together
• Covalent bonds form between non-metals when they share pairs of electrons
• Ionic compounds consist of positively charged metal cations and negatively charged non-metal anions held together by electrostatic forces of attraction
• Ionic compounds contain metal and non-metal elements that have formed ionic bonds
• Metallic bonds occur within metals, where positive metal ions are held by delocalised sea of electrons
• Compounds: substances that contain 2 or more different elements chemically bonded. Elements involved are always found in the same proprtions
• Mixtures: consists of 2 or more substance that are not chemically combined because they haven’t reacted. Can be easily separated (by physical methods)
• Ions are formed when atoms gain or lose electrons. They do this to have a full outer shell and be more stable
• Ionic bonds are strong electrical forces of attraction between oppositely charged ions. Form ionic compounds
• Chromatography: On a chromatography paper draw a pencil line 2cm from the bottom. Using a capillary tube add small spots of each substance on the pencil line, each with the same distance between them (1cm). Then in a beaker add 1cm of solvent ( so the line is not submerged), place the paper in the beaker. Put a lid on the beaker and allow the solvent to travel up through the paper.
• Neutralisation: Add dilute hydrochloric acid into a beaker. Measure and record the pH of the contents of the beaker, by using universal indicator paper or a pH meter for more accurate answer. Then add a small mass of calcium hydroxide powder to the beaker stir and measure and record the pH again. Repeat until the pH no longer changes.
• Crystallisation: Used to produce solid crystals from a solution.

  The solution is heated to remove enough solvent to produce more saturated solution, as solvent starts evaporating the remaing solution becomes more concentrated. Saturated solution is cooled. Crystals form in the solution, the crystals are separated from the liquid and dried.
• Diamond and Graphite are giant covalent structures (very strong).
• Diamond: Each carbon atom is covatenly bonded to 4 carbon atoms, regular 3D pattern, high melting point because the covalent bonds are strong, doesn't conduct eelctricity because it has no free electrons or ions that can move around.
• Graphite: Each carbon atom is bonded to 3 carbon atoms, large flat sheets arranged on top of each other to make layers, layers are held together weakly as there is no covalent bonds, soft because the layers are free to slide, high melting point because layers are strongly held together with covalent bonds, conducts electricity and heat because it has delocalised electrons.
• Graphene: Giant molecular substance, single layer of graphite, carbon atom is covalently bonded to 3 other carbon atoms, regular lattice structure, conducts electricity because the non-bonding outer electrons become delocalised and can move through the structure, strong and flexible because has many strong covalent bonds, transparent.
• Fullerenes: Buckyballs- conduct electricity because they have delocalised electrons, soft when in the solid state as they have weak intermolecular forces. Used for : acting like a cage around other molecules, industinal catalysts. Nanotubes:conduct electicity,very strong, used to strengthen materials due to very high length : diameter ratio.
• Pure substance- contains only one type of compound or element, they melt and boil at specific temperatures. Impure substances- contains more than one type of atom, they melt at range of temperatures, having impurities will lower the melting point and increse the boiling point.
• Making insoluble salts: 1-mix solution of two substances that will form insoluble salt. 2-Filter the mixture. The insoluble salt will be trapped in the fliter paper.3- Wash the salt with distilled water. 4- Leave the salt to dry on the filter paper.
• What must be added so vapour doesn't escape?

  A bung
• Water treatment stages

  Sedimentation- put waste in water tank, leave it to settle, large insoluble particles sink to the bottom of a tank to form a sludge. Filtration- small insoluble particles are removed by filtering through beds of sand. Chlorination- chlorine gas is bubbled from the water to kill microbes.
• Electrodes must be

  Inert and conductors of electricity
• Why does Buckminster fullerene have low melting point and is slippery


  There are weak intermolecular forces between the molecules. Therefore, only need a little bit of energy to overcome them.
• Dynamic equilibrium


  The concentration of products and reactants remains constant. The rate of the forward reaction is equal to the rate of backward reaction.
• Haber process

  Temperature- 450°C Pressure- 200 atmospheres Catalyst- iron
• Haber process


  If pressure increased the equilibrium will shift to the side with the fewer moles.
• Higher pressures can be dangerous or expensive to maintain
• Stages of the life cycle assessment

  Stages: 1.Extracting and processing raw materials. 2. Manufacturing and packaging the product. 3. Using the product. 4. Disposing of the product.
• An ion is a charged particle formed when an atom or a group of toms gain or lose electrons.