3.2.3-Group 7 Halogens Flashcards
Trends in boiling point down group 7
Increases down group
Increased size makes the van der waals forces increase
More energy required to separate molecules
Trends in electronegativity down group 7
Decreases down group
Increased nuclear charge because more protons but
Increasing number of shells therefore more shielding
Increasing atomic radius therefore attraction drops as distance increases
Atomic size down group 7
Increases down group
Ionic size down group 7
Increases down group
Greater atomic number the more electrons there are which go into shells further away
Ions are larger than atoms due to repulsion from added electrons
Oxidising power of group 7 down group
Halogens are oxidising agents Weaker down the group Nucleus attraction affected by Increased nuclear charge is offset by Increased shielding Increased atomic radius
What does chlorine oxidise
Bromide ion to bromine
Iodide ions to iodine
What does bromine oxidise
Iodide ions to iodine
What does fluorine do as an oxidising agent
Has small size and high electronegativity
So
Brings out highest oxidation energies
Stronger to weakest oxidising agents in group 7
Cl2 Strongest
Br2
I2 Weakest
Why does oxidising agent down group 7 get weaker
When a halogen acts as an oxidising agent it gains an electrons and is reduced
Down group becomes harder because atoms are larger and experience more shielding
What is the order of reducing power in group 7
Strongest I-
Br-
Cl-
Weakest F-
Explain the trend in reducing power of halide ions
When a halide ion acts as a reducing agent it loses electrons given to reduced species
Down group it becomes easier to loads an electron because ions are larger and their is more shielding.
Halide ions tests
Add nitric acid to remove any other ions
Add silver nitrate produces a precipitate for Cl-, Br-, I-
Add ammonia (dilute and conc) used to see if precipitate redissolves to help confirm identity
What will F - show in the halide ion tests and why
No visible change
Silver fluoride is soluble in water
What does Cl- produce with a halide ion tests
White precipitate
Ag+ + Cl- –> AgCl
Predicate dissolves in dilute ammonia
What does Br- produce in halide ion tests
Cream precipitate produced
Ag+ + Br- –> AgBr(s)
Doesn’t dissolve with dilute NH3
Does dissolve in concentrated NH3
What does I- show produce halide ion tests
Yellow precipitate
Ag+ + I- –> AgI (s)
Insoluble in dilute NH3
Insoluble in concentrated NH3
Uses of silver salts
[Ag(NH3)2] +
Tollebs reagent tests for aldehydes
[Ag(CN)2] 2-
Silver plating
[Ag(S2O3)2]3-
Photographic fixer
Reaction of chlorine with water
Cl2(g) + H2O(l) = HCl(aq) + HOCl (aq)
Reaction of chlorine with water in sunlight
2Cl2 +2H2O –> 4HCl + O2
What happens to litmus paper in chlorine water
Red due to acidity of HCl
Bleached white by oxidising power of HOCl
Equation for manufacture of bleach
2NaOH(aq) + Cl2(g) -> NaCl + NaOCl+H2O
Uses of chlorine
Water purification Bleach Solvents Polymers CFC's
Uses of fluorine
CFC
Polymers
Uses of Fluoride
Helps prevent tooth decay
What does water purification do
Prevents spread of water born diseases e.g. Cholera, typhoid, dysentery
Argument against water purification
React with organic matter to form thhalomethanes are linked to with cancer
Taste factor
Quantity of substance influences toxicity
