M3 B3 Group 7
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What are group 7 elements known as?
The Halogens
What type of molecule do halogens form??
Diatomic molecules (2 atoms per molecule)
What type of structure do halogen molecules have?
Simple molecular (London forces between molecules)
At RTP, What are the states of the following elements: - Flourine - Chlorine - Bromine - Iodine
• Flourine- Gas • Chlorine- Gas • Bromine- Liquid • Iodine- Solid
What is the trend in melting point and boiling point down group 7?
Melting/ boiling point INCREASES down group 7. • Number of electrons increases so greater uneven electron distribution. • Stronger induced dipole-dipole attractions. • So more energy is required to break the attractions between molecules. • Hence mpt/ bpt increases.
Define: Volatility
This is the ease in which a liquid turns into a gas.
What is the trend in volatility down group 7?
Volatility DECREASES down group 7. - There is an increase in the number of electrons - Increases uneven distribution of electrons - This creates stronger induced dipole-dipole attractions. - So more energy is required to overcome the attraction between molecules.
What is the trend in Reactivity down group 7?
Reactivity DECREASES down group 7. - Down the group, the atoms have more electron shells. - More shielding of nuclear charge - Less nuclear attraction for incoming electrons. - Electrons are gained less easily by Iodine than Chlorine.
What is electron affinity, and does chlorine have a greater or lower electron affinity than bromine?
Electron affinity is an atoms ability to attract electrons. Chlorine has a greater electron affinity for electrons than bromine or iodine.
Define: oxidising ability/ power?
This is the ability of an atom or species to oxidise another species (take an electron from it)
What colour are the following Elements in water and cyclohexane: - Chlorine - Bromine - Iodine
Water: - Chlorine- Pale green - Bromine- Orange - Iodine- Brown Cyclohexane: - Chlorine- Pale green - Bromine- Orange - Iodine- Purple
Define: Displacement
A reaction in which a more reactive element displaces a less reactive element from an ionic compound in aqueous solution
The more reactive halogen TAKES electrons from the less reactive halide (oxidises it), why is this? (use chlorine as an example)
• Cl has less electrons shells than Br- or I-. • Cl therefore has less shielding. • Cl has more nuclear attraction for electrons • Cl takes electrons from Br- and I-
What is the reaction for chlorine with water?
Chlorine + water = hydrochloric acid + chloric acid. (HClO)
What is a disproportionation reaction?
This is a reaction which ans the same element is both reduced and oxidised (ox. no. increases and decreases).
What is the reaction used for the sterilisation of water? And what is the main product?
Chlorine + water = chloric acid and hydrochloric acid The HOCl forms reactive oxygen atoms that destroy bacteria in water.
What reaction is used in the production of bleach?
Chlorine + sodium hydroxide = Sodium chlorate (NaClO) and sodium chloride and water
What are the key issues with using chlorine?
• Chlorine is a toxic gas • It is corrosive and irritating to the eyes and skin and mucous membranes. • Causes vomiting, nausea, dizziness, headaches and coughing. • May react with organic matter (rotting vegetation) to form Trichloromethane (traces of hydrocarbons)