Group 7
Why are the halogens more soluble in cyclohexane than in water
- The halogens which are non polar molecules mix easily with cyclohexane, which is also non-polar. - easy mixing is possible where the intermolecular forces between solute and solvent molecules are about the same strength, the halogens and cyclohexane both form London forces which are similar in strength. - water is a polar substance and so can form hydrogen bonds that iodine can't
How do you show you have a solution of iodine
1) add an ORGANIC SOLVENT and shake the solution, halogens are more soluble in organic solvents, iodine will turn purple in the organic layer which is the upper layer because its less dense 2) Add starch and shake. Iodine will change from brown -> blue black
What is the problem in distinguishing between bromine and iodine solutions?
Both solutions can appear brown depending on the concentration of the solutions
State the solubility of chlorine, bromine and iodine in water
Cl2 - slightly soluble, Br2 - slightly soluble, I2 - slightly soluble
describe the reaction between hot iron and chlorine
Hot iron burns brightly in chlorine forming iron chloride
What happens to the intermolecular forces of the halogens as you go down the group and why
The London forces increase between the molecules due to the increasing number of electrons
Explain the trend in oxidising power of the halogens
The fewer the number of shells, the less shielded the electrons are from the nucleus. The attraction of the electrons to the nucleus is therefore stronger and the atom is likely tp accept electrons
Explain the trend in reducing power of the halides
The more electron shells, the more shielding of the nucleus and the outer electrons become less strongly held. Therefore they are lost more easily and the halide ion is more readily oxidised
How do displacement reactions between halogens and halide ions work?
The more reactive halogens (the strongest oxidising agents) will displace the more reactive halides (the strongest reducing agents) from solutions of their ions I.e. chlorine will displace bromide and iodide ions from solution
Iodine reacts with metals to form...
covalent halides
What colour and state is iodine in pure form
dark grey solid
What colour and state is bromine in pure form
dark red/ brown LIQUID
Trend of oxidising power of halogens
decreases down a group, fluorine being a very strong oxidising agent and iodine mild
Trend of reducing power of halides
increases down group, iodide is a good reducing agent and fluoride is a very poor reducing agent
Why does iodine form a brown precipitation if excess KI is present
iodine reacts with the iodide ions to from trioxide ions which give the solution its brown colour
Chlorine and bromine react with S block metals to form...
ionic halides
Why is fluorine not used in laboratories
it is too dangerous
Uses of bromine
make flame retardants, medicines and dyes
uses of chlorine
manufacture of PVC, kill bacteria in drinking water, bleach paper + textiles
uses of iodine
medicines, dyes and catalysts
the larger the molecules the ... polarisable
more
What is observed in the reaction: Cl2(g) + 2Br(aq) -> 2Cl-(aq) + Br2(aq)
orange colour will appear in solution on adding chlorine
Bromine colour in non-polar solvents
orange solution
What colour and state is chlorine in pure form
pale green GAS
What colour and state is flouring in pure form
pale yellow gas
Iodine colour in non-polar solvents
purple solution
what is electronegativity?
the ability of an atom to attract electrons in a covalent bond
Why does the electronegativity of group 7 decrease down the group
the atomic radius increases and so the shielding increases so the electrons in the covalent bond are further from the nucleus and are therefore less strongly attracted to the nucleus
Uses of flourine
the manufacture of the very slippery, non-stick polymer poly(tetraflourethene)
What happens to the melting and boiling temps as you go down group 7
they become higher
How are the halogens oxidising agents
they can accept electrons and get reduced
Are the halogens volatile
yes