Chemistry Unit 1 Edexcel Notes (AS Level)

MODEL ANWERS MODEL ANSWERS Why Magnesium has higher melting point than sodium 1. Mg2+ has a smaller ion (Magnesium ions are smaller than sodium ions) 2. Mg2+ has a larger charge than sodium ions 3. Contributes more electrons to sea of electrons 4. Stronger attraction between positive ions and delocalised electrons 5. More energy/heat required to overcome bonds Why ionisation energy increases across a period 1. More protons; a greater nuclear charge 2. The outer electrons stay in the same shell; same shielding 3. Overall greater force of attraction between nucleus and outer electrons Enthalpy change of formation 1. Energy change when 1 mol of a compound is formed from its elements 2. Under standard conditions of 298K and 1atm Enthalpy change of reaction 1. Enthalpy change when the number of moles of reactants reacts as stated in the balanced equation First Ionisation Energy definition 1. The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms; to form 1 mole of gaseous ions 2. Give equation (X —> X+ and e-) Bond Enthalpy definition 1. The average amount of energy needed to break one mole of covalent bonds in the gaseous state Stereoisomerism 1. Occurs in alkenes due to the restricted rotation about the C=C bond 2. Alkanes can freely rotate about their bond; they are simple single bonds 3. E.g. hex-2-ene has isomers because it has different groups attached to the C=C carbons; unlike hex-1-ene which has 3 groups of hydrogen, so it cannot exist as isomers Hazard 1. Potassium Hydroxide solution is corrosive and can damage skin or eyes 2. Hydrogen is flammable/explosive MAKING SALTS 1. Filter (to remove any impurities) 2. Boil/heat to reduce the volume of water 3. Cool and allow crystals to form 4. Filter again 5. Wash with a small volume of water and dry with filter paper Theoretical Lattice vs normal 1. The theoretical lattice will be less exothermic 2. Due to the degree of covalent character; as a result of polarization of the bond 3. There is deviation from the ionic model (100% ionic bonding) Which element has highest ionisation energy (justify) 1. Helium; the electron removed would be close to the nucleus which has a large nuclear charge 2. It does not experience any/little shielding Why the second ionisation energy is higher 1. Electron being removed from positive ion; electron removed is closer to the nucleus 2. The proton:electron ratio is greater in the 1+ ion; remaining electrons more tightly held 3. Greater attraction between nucleus and outer electrons 4. Less repulsion in the new ion Why cracking is important 1. Produces shorter chain alkanes (e.g. diesel); lighter fractions are more useful and are more in demand 2. It produces short chain alkenes which can be used to make plastics/polymers Why reformed cyclic hydrocarbons are advantageous 1. They promote efficient combustion and burn more easily Why ionisation energy increases 1. nuclear charge increases 2. same number of shells/outer electrons in same shells 3. overall greater force of attraction between positive nuclei and outer electrons 4. distance from nucleus is less

Reactions of Alkenes - Bromine; add 2 Br groups

- Bromine water; add Br and OH - Hydrogen halide; add H and X (halide ion) - Potassium Manganate; add two OH groups