GROUP 2 (Alkaline earth metals) & Halogens (Group 7)
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What is the trend in reactivity from Mg > Ba?
• Shielding increases • nuclear attraction on outer e- decreases • atomic radius increases • IE decreases
What is the observation of Mg reacting with oxygen?
• bright light • white solid is formed In an element more reactive than Mg solid is formed at a faster rate, light is brighter and bubbling is vigorous
What is the trend in solubility of the group 2 hydroxides?
• Mg(OH)₂ - very sparingly soluble >forms a white precipitate • Ca(OH)₂ - sparingly soluble • Sr(OH)₂ - slightly soluble • Ba(OH)₂ - soluble Hydroxides are more soluble as you go down the group
What happens to the pH of hydroxides in group 2?
pH increases - more OH⁻ ions are in solution so the solution is more alkaline as you go down the group
What are the products when a metal reacts with an acid?
Salt and hydrogen - remember MASH M - metal, A - acid, S - salt, H - hydrogen
What are the products of a neutralisation reaction?
Salt and water - CO₂ if there is a carbonate ion
What is the industrial use of Magnesium hydroxide?
To neutralise excess stomach acid
What is industrial use of calcium hydroxide?
Neutralises acidic soils (H₂SO₄)
What is industrial use of calcium carbonate?
• Known as chalk or marble • Thermal decpmosition gives CaO which is used to make cement
What is the alkalline gas you need to know?
NH₃
What is trend in electronegativity as you go down group 7?
Electronegativity decreases * no. of shells increases * shielding increases * weaker attraction between nucleus and electrons in a covalent bond
What is the trend in boiling point as you go down group 7?
BP increases * no. of e- increases * stronger london forces between the molecules * more energy needed to overcome the forces
What is the appearance of the halogens at room temp, Aq solution and organic liquid?
Why do you need to add organic liquid to a test tube containing a halogen?
Br₂ & I₂ solution are similar in aqueous solution so organic liquid allows distinctly different colours to be seen
What is an oxidising agent?
Electron acceptor
Why does the ability of a halogen to act as an oxidising agent decrease as you go down the group?
• shielding increases • atomic radius or no. of shells increases - nuclear attraction decreases • ability to accept e- decreases • reactivity decreases Strength in decreasing order: fluorine, chlorine, bromine & iodine
TRUE or FALSE: Chlorine can be both oxidised and reduced in the same reaction
TRUE - called disproportionation
What is disproportionation?
Oxidation and reduction of the same element
What happens if universal indicator paper is added to chlorine water?
• Turns red because both products are acids i.e. HCl & HClO • Red colour disappears and indicator turns white because HClO is an effective bleach
How is chlorine used in water treatment?
• Sterilises drinking water & water in swimming baths • Toxic so can only be used in small amounts • If levels are not controlled chlorine in water can react with organic comnpounds to form chlorinated hydrocarbons
What is observed when a chloride ion reacts with silver nitrate?
White precipitate
What is observed when a bromide ion reacts with silver nitrate?
Cream precipitate
What is observed when a iodide ion reacts with silver nitrate?
Yellow precipitate
Why add nitric acid before adding silver nitrate?
• Solutions often contain carbonate ions and hydroxide ions naturally - they create false white precipitates of silver carbonate & silver hydroxides • They must be removed from the solution before testing for halide ions