group 2 and group 7
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what is redox chemistry
where one species becomes oxidised and the other becomes reduced
what is the trend in reactivity of group 2 metals, down the group
group 2 metals become increasingly reactive down the group atomic radius increases electron shielding increases therefore nuclear attraction decreases, so the outermost electron is more easily lost.
what is the product(s) when group 2 metal oxides react with water
metal hydroxides only.
what is the trend in solubility down group 2
metal hydroxides become increasingly soluble as the solutions they form are more strongly alkaline.
does BeO react with water
no
state 3 uses of group 2 compounds
• Ca(OH)2 is used to neutralise acidic soil • Mg(OH)2 and CaCO3 are used as ‘antacids) used to treat heartburn
what type of bonding is present in group 7 atoms, how does this bonding occur
london forces • electrons are in constant motion • electrons become unevenly distributed in the molecule • this results in a temporary dipole • the temporary dipole causes electrons in a neighbouring molecule to be repelled, causing an induced dipole
what is the trend in boiling point down group 7
boiling point increases down group 7 - down the group the number of electrons in each molecule increases - therefore there is a greater uneven distribution of electrons causing a larger temporary dipole - resulting in stronger london forces which recquire more energy to overcome.
what is the trend in volatility of group 7 down the group
decreases, more energy is required to overcome the forces between the molecules and hence the molecules become more difficult to separate
what is the difference between halogens and halides
halides are the negative ions of halogens halogens are non-metals and are diatomic molecules at room temperature (group 7)
what is the trend in oxidising ability down group 7
they become weaker oxidising agents down the group, they gain electrons to form 1- ions with decreasing ease this is because: - atomic radius increases - electrons shielding increases therefore nuclear attraction decreases so they become less attractive to electrons.
what are displacement reactions
where the halogen “steals” an electron from a halide ion the halogen displaces the halide
write out the equation for the displacement reaction of chlorine molecule reacting with the halide bromide
Cl2 + 2Br - —–> 2Cl- + Br2
how do displacement reactions work
halogens can only displace halides lower down in the group than themselves this is because the halogen is the stronger oxidising agent
what is the appearence of chlorine in water
pale green
what is the appearence of chlorine in cyclohexane
pale green
what is the appearence of bromine in water
orange
what is the appearence of bromine in cyclohexane
orange
what is the appearence of iodine in water
brown
what is the appearence of iodine in cyclohexane
purple
what is a disproportionation reaction
when the same species is both oxidised and reduxed in the same redox reaction
what are the advantages and disadvantages of adding chlorine to water
+ - kills bacteria • can form carcinogenic hydrocarbons + chlorine gas is toxic
what are other methods of water purification, what are the drawbacks
• use of ozone to purify water in swimming pools (expensive) • UV light purified water can become contaminated after treatment so is less effective than chlorine
what is the equation of chlorine reacting with water
Cl2 (g) + H2O (l) —> HClO(aq) + HCl(aq)