what do we know about fluorine, chlorine and bromine?

What do we know about fluorine, chlorine and bromine?

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Group 7

1. Explain the trend in boiling points of Cl2, Br2, and I2 in terms of Van der Waals’ forces.

2. Explain reactivity of the halides with reference to negative ions, atomic size, shielding and nuclear attraction.

3. Interpret and make predictions from the chemical and physical properties of Gp 7 elements and their compounds.

Quick Check of Forces

Put these ‘attractions’ in order of strength:

• Covalent/ionic/metallic bonds

• Van der Waals forces

• Permanent dipole-dipole forces (e.g. hydrogen bonding)

Boiling points – Explain the pattern

Practical

Complete the practical on your sheet, and describe the trend for reactivity of halides.

What does displacement mean?

Explain the reactivity of the halides

Key Words

Negative ions

Atomic size

Shielding

Nuclear attraction

Redox Reactions

½ Cl2 + e- Cl-

Interpreting and predicting properties

1) Which halogen has a lower boiling point than chlorine and why?

2) What will happen when aqueous NaBr is put in a test tube with Cl2?

3) Which of H-F and H-Br will have the largest dipole (and therefore higher boiling point)?

Group 7 – The Halogens

1) Describe the precipitation reactions, including ionic equations, of the aqueous Cl-, Br- and I- with silver ions followed by aqueous ammonia. 2) Describe the use of precipitation reactions as a test for the different halide ions.

Practical

Complete the practical to positively identify the halogen ions.

Then describe (in bullet points) how these tests are useful for identifying ionic compounds containing halogen ions.

Question: What would you expect for Astatine?

Independent study

Contrast the benefits and associated risks of using chlorine in water treatments.

Bullet points – you will be tested on Thursday.

Chlorine – Good or bad!

Group 7 – Redox and disproportionation

1. Describe the redox reactions of Gp 7 elements, including ionic reactions, in the presence of organic solvent to illustrate relative reactivity of Gp 7.

2. Describe the term disproportionation as a reaction in which an element is simultaneously oxidized and reduced.

Two group 7 experiments

Displacement due to different reactivity.

Colour change.

Shows up better with an organic solvent.

Test for Group 7 ions.

Add nitric acid.Add silver nitrate.

Ag+(aq) + X-

(aq)AgX(s)

A new type of redox reaction…Disproportionation

Reaction to make bleach - Sodium chlorate (I):

2NaOH(aq) + Cl2(aq) NaClO(aq) + NaCl(aq) + H20(l)

Why chlorine kills bacteria in swimming pools (and drinking water)

H20(l)+ Cl2(g) HCl(aq) +HClO(aq)

Attempt Exam questions on p47

1) Try yourself

2) Then ask a friend or Mr Boorman