3.1.3. The Halogens Flashcards
What group are halogens found in on the periodic table?
Group 7
List 2 properties of halogens
Low boiling and melting points
Exist as diatomic molecules
Explain the trend in boiling point down group 7
Boiling point increases down the halogen group.
Number of electrons increases.
Stronger London forces between molecules.
More energy required to overcome London forces between molecules.
Explain the trend in reactivity down group 7
Reactivity decreases down group 7.
Atomic radius and electron shielding increases.
Nuclear attraction decreases.
Ability to gain an electron to form a 1- ion decreases.
Explain the trend of oxidising ability down group 7
Oxidising ability decreases down the group.
Atomic radius and electron shielding increases.
Nuclear attraction decreases.
Ability to gain an electron to form a 1- ion decreases.
Explain the reducing ability down the group
Reducing ability increases down the group.
Atomic radius and electron shielding increases.
Nuclear attraction between positive nucleus and outermost electrons
decreases.
Electron is more easily lost.
What is the reaction called, when a more reactive halogen replaces a less reactive halide?
Displacement
Colour of chlorine in water and cyclohexane
Pale green
Colour of bromine in water and cyclohexane
Orange
Colour of iodine in water and cyclohexane
Water - brown
Cyclohexane - violet
Order Cl-, Br- and I- in order of strongest to weakest oxidising agent
Cl-, Br-, I-
Write the equation for chlorine oxidising bromide ions
Cl2 (aq) + 2Br (aq) -> Br2 (aq) + 2Cl- (aq)
Define disproportionation
Reduction and oxidation of the same element in the same redox reaction
The equation of Cl2 and water. Using oxidation numbers, Explain why this is a disproportionation reaction.
Cl2 (g) + H2O (l) -> HCl (aq) + HClO (aq)
Cl2 = 0
Cl in HCl = -1 reduction
Cl in HClO = +1 oxidation
What is a benefit and a risk of adding chlorine to drinking water?
Benefit - Kills bacteria
Risk - Toxic
What are the two forms of chlorate ion?
ClO- is chlorate (I)
ClO3- is chlorate (V)
Equation for forming bleach
Cl2 (g)) + 2NaOH (aq) -> NaCl (aq) + NaClO (aq) + H2O (l)
What colour precipitate is formed when acidified silver nitrate (AgNO3) is added to Cl-, Br- and I-
Cl- = white precipitate (AgCl)
Br- = cream precipitate (AgBr)
I- = yellow precipitate (AgI)
How is ammonia (NH3) used identify halide in solution after forming precipitate with silver nitrate?
AgCl dissolves in DILUTE NH3
AgBr dissolves in CONCENTRATED NH3
AGI doesn’t dissolve in NH3
