- Atomic Radius Decreases Across A Period.
- Number of protons increases, so the positive charge of the nucleus increases.
- Electrons are pulled closer to the nucleus, so atomic radius decreases.
- Shielding doesn't change because the extra electrons gained are added to the outer energy level.
- Ionisation Energy Increases Across A Period.
- Number of protons increases, causing a stronger nuclear attraction.
- Extra electrons are roughly the same energy level, so there is little shielding or extra distance to lessen the nuclear attraction.
- Ionisation Energy Decreases Down A Group.
- There are extra electron shells, so there is weaker nuclear attraction.
- The shielding between the outer electrons and the nucleus overcomes the nucleus' positive charge.
- Melting & Boiling Point Increase Across A Period.
- Metals: The metallic bonds get stronger; increasing number of delocalised electrons and decreasing ionic radius. Higher charge density.
- Macromolecular: Atoms are linked by strong covalent bonds, lots of energy needed to break the bonds.
- Simple Molecular Substances: Van der Waals' forces are easily overcome.
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Group 2 - The Alkaline Earth Metals
- Group 2 elements lose their outer electrons to form 2+ ions.
- Reactivity increases down group 2. When they react, they lose electrons. The easier it is to lose electrons, the more reactive the element.
- Group 2 elements react with water to produce hydroxides.
- Metal Hydroxide + Hydrogen
- They burn in oxygen to form solid, white oxides.
- Group 2 oxides and hydroxides are bases.
- They form alkaline solutions in water.
- The oxides form more strongly alkaline solutions as you go down the group
- Hydroxides become more soluble.
- Thermal Decomposition: When a substance breaks down when heated.
- Group 2 carbonates decompose to form the oxide and carbon dioxide.
- Thermal stability increases down the group, so it takes more heat to decompose carbonates.
- Group 2 compounds are used to neutralise acidity.
- Calcium Hydroxide [Ca(OH)2] is lime; used to neutralise soils.
- Magnesium Hydroxide [Mg(OH)2] is an antacid.
- H+ (aq) + OH- (aq) --> H2O (l)
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Group 7 - The Halogens
- Boiling and melting point of halogens increase down the group.
- Due to increased strength of van der Waals forces.
- Halogens become less reactive down the group.
- They react by gaining an electron - they are oxidising agents.
- Shielding increases, so attraction is lower.
- Halogens displace less reactive halide ions.
- F > Cl > Br > I > Al
- Silver Nitrate Solution is used to test for halides.
- Chlorine --> White precipitate.
- Bromine--> Cream precipitate.
- Iodine --> Yellow precipitate.
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Disproportionation & Water Treatment
- Halogens undergo disproportionation with alkalis.
- Chlorine and Sodium Hydroxide make bleach
- 2NaOH + Cl2 --> NaClO + NaCl + H2O
- Chlorine is used to kill bacteria in water.
- Chlorine + water = disproportionation.
- Cl2 + H2O --> HCl + HClO (reverisible reaction)
- Aqueous chloric (i) acid ionises to make chlorate (i) ions.
- Chlorate (i) ions kill bacteria.
- Adding chlorine makes water safe to drink and swim in.
- Benefits Of Chlorine In Water:
- It kills disease-causing microorganisms.
- It prevents reinfection further down the water supply.
- It prevents growth of algae.
- Risks Of Chlorine In Water:
- Chlorine gas is very harmful if inhaled.
- Chlorine reacts with organic compounds in water to form chlorinated hydrocarbons.
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