2.3 Group 7 Flashcards
Explain the trend in atomic radius down group 7:
- increases down the group
- shells/shielding increases
- nuclear attraction on the outer electron decreases
Why is the ionic radius bigger than the atomic radius?
- the same number of protons are attracting one more electron
Explain the trend in boiling points in group 7:
- increases down the group
- X2 molecules increases in size so number of electrons increases
- stronger Van der Waals forces between molecules
- more energy needed to overcome forces
Explain the trend in electronegativity down group 7:
- decreases down the group
- shells/shielding increases
- nuclear attraction on the shared pair of electrons decreases
Explain the trend in 1st ionisation energy down group 7:
- decreases down the group
- shells/shielding increases
- nuclear attraction on the outer electron decreases
- less energy needed to remove the outer electron
Colour of Cl2 (normal/aqueous/cyclohexane)
Normal: pale green
Aqueous: pale green
Cyclohexane: pale green
Colour of Br2 (normal/aqueous/cyclohexane)
Normal: red/brown
Aqueous: orange
Cyclohexane: orange
Colour of I2 (normal/aqueous/cyclohexane)
Normal: grey
Aqueous: brown
Cyclohexane: purple
Describe the solubility of the halogens:
- solubility in water decreases down the group as the halogen molecule becomes larger
- halogens are more soluble in non-polar solvents (e.g. cyclohexane) than in water
Why are halogens good oxidising agents?
- they like to gain (accept) electrons
Explain the trend in the ability of the halogens to act as oxidising agents down the group:
- decreases down the group
- atomic radius increases
- shells/shielding increases
- nuclear attraction on the outer electron decreases
- ability to gain electrons decreases
KEY DEFINITION: disproportionation
- a redox reaction in which the same element is both oxidised and reduced
Give the equation and name for the reaction between chlorine and water:
Cl2 + H2O «» HCl + HClO
* disproportionation
Observations when chlorine is present:
Pale green colour
Observations when HCl is present:
- universal indicator turns red
Observations when HClO is present:
- universal indicator turns white (bleach)
Give the equation for the reaction between chlorine and water in the presence of sunlight:
2Cl2 + 2H2O»_space; 4HCl + O2
(the chloric-1-acid initially formed decomposes in sunlight to form HCl and O2)
What are the risks and benefits of using chlorine in water treatment?
Benefits: kills bacteria/microorganisms
Risks: toxic
Give the equation and name of the reaction between chlorine and cold dilute NaOH?
Cl2 + 2NaOH»_space; NaCl + NaClO + H2O
- disproportionation
What happens in the reaction between chlorine and cold dilute NaOH?
- the green colour of the chlorine fades
- the smell becomes less pungent
What is one use of NaClO?
Domestic bleach
Describe a method to test for halide ions:
- make a solution of the substance to be tested
- add dilute nitric acid to remove unwanted ions
- add silver nitrate solution
- observe the colour of the precipitate
Why is it necessary to add dilute nitric acid when testing for halide ions?
- to remove unwanted ions (e.g. carbonates) that may interfere with the test results by also giving precipitates
Observation and product of Cl- ions and AgNO3:
- white precipitate
- silver chloride (AgCl)
