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A-level Chemistry: Group 7, The Halogens Part 1

Chemistry35 CardsCreated 2 months ago

This deck covers key concepts about Group 7 elements, the halogens, including their physical properties, chemical behavior, and reactions.

What colour is fluorine?

Pale yellow
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Key Terms

Term
Definition
What colour is fluorine?
Pale yellow
What colour is chlorine?
green
What colour is bromine?
red-brown
What colour is iodine?
grey
What physical state is fluorine at room temperature?
gas
What physical state is chlorine at room temperature?
gas

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TermDefinition
What colour is fluorine?
Pale yellow
What colour is chlorine?
green
What colour is bromine?
red-brown
What colour is iodine?
grey
What physical state is fluorine at room temperature?
gas
What physical state is chlorine at room temperature?
gas
What physical state is bromine at room temperature?
liquid
What physical state is iodine at room temperature?
solid

Boiling points _____ down the group

increase

Why do boiling points increase down the group? (3)

  • ∵ Van der Waals forces between molecules

  • Increase with size or Mr or surface area

  • More energy needed to overcome these forces

Trend is shown in changes of physical state from fluorine (gas) to iodine (solid))

Electronegativity _______ down the group
decreases

Why does electronegativity decrease down the group? (2)

  • Shielding increases or the atomic size increases

  • Weaker attraction by nucleus for bonding pair of electrons in the covalent bond

Halogens become _____ oxidising down the group
less
Why do halogens become less oxidising down the group?
Get less reactive down the group ∵ atoms become larger Outer shell further away from nucleus ∴ electrons less attracted to it
How can you see the relative oxidising strengths of halogens?
By displacement reactions with halide ions

What is the basic rule for halogens in a displacement reaction with halide ions

A halogen will displace a halide from solution if the halide is below it in the periodic table

What can we use these displacement reactions (halogens and halides) for?
To help identify which halogen (or halide) is present in solution
Why can’t you investigate fluorine in aqueous solution?
∵ it reacts with water
Name 2 uses of chlorine
Used to kill bacteria in water Mix it with sodium hydroxide to make bleach
Describe how you get bleach
If you mix chlorine gas with cold, dilute, aqueous sodium hydroxide, you get sodium chlorate(I) solution (NaClO(aq)) = bleach

Write an equation to show how bleach is made

Cl₂(g) + 2NaOH(aq) → NaCl(aq) + NaOCl(aq) + H₂O(l)

Write the oxidation states of chlorine in this equation

  • In Cl₂ → 0

  • In NaCl → –1

  • In NaOCl → +1

What do the oxidation states of chlorine in this equation tell us?

Oxidation state of Cl goes up and down, meaning chlorine is both oxidised and reduced. This is called disproportionation.

Name 3 uses of sodium chlorate(I) solution (bleach)
Water treatment (kills bacteria) Bleach paper and textiles
When you mix chlorine with water, what does it undergo?
Disproportionation

Write an equation to show the reaction of chlorine with water to form chloride ions and chlorate(I) ions. Include the oxidation states for chlorine.

Cl₂(aq) + H₂O(l) → Cl⁻(aq) + ClO⁻(aq) + 2H⁺(aq)

Oxidation states of chlorine:

  • In Cl₂ → 0

  • In Cl⁻ → –1

  • In ClO⁻ → +1

In sunlight, what can chlorine do to water & what does this form?
Can decompose water to from chloride ions and oxygen

Write an equation to show the reaction of chlorine with water to form chloride ions and oxygen

2Cl₂(aq) + 2H₂O(l) → 4Cl⁻(aq) + O₂(g) + 4H⁺(aq)

______ ____ kill bacteria
Chlorate(I) ions
Chlorine is ___
toxic
Name 3 advantages of adding chlorine to water supplies
Chlorine is important part of water treatment
Describe disadvantages of adding chlorine to water supplies (3)
Risks from using chlorine to treat water
Reducing Power of Halides Down the Group
Increases
Why does the reducing power of halides increase down the group?
(To reduce something, halide ion needs lose electron from its outer shell)
Describe the test for halides
Add dilute nitric acid (HNO3) and then silver nitrate solution (AgNO3) Precipitate is formed (of silver halide)