3. Group 7, the halogens
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What is electronegativity?
The power of an atom to attract the electrons in a covalent bond
What happens to electronegativity down group 7?
It decreases
Why does electronegativity decrease down group 7?
• atoms get larger down group so outer electrons are further from nucleus • outer electrons are more shielded
What happens to boiling point down group 7?
It increases
Why does boiling point increase down group 7?
• halogens are simple molecular so held together by VDWs * strength of VDWs ↑ as size of the molecule ↑ (i.e. number of electrons within the molecule ↑)
Why do larger molecules have stronger VDWs forces?
More electrons present, so greater asymmetrical distribution of charge
What is oxidising ability?
The ability for elements to accept an electron to become ions
What is the oxidising ability of halogens?
The ability of the halogens to accept an electron to become halide ions
Are halogens good oxidising agents?
Yes
Why are halogens good oxidising agents?
They have the ability to accept an electron to become halide ions
What happens to oxidising power down group 7?
It decreases
Why does the oxidising power of the halogens decrease down group 7?
• atomic radius ↑ • more shielding • therefore worse at gaining an electron due to ↓ nuclear attraction
Where can the trend that the oxidising power of the halogens decreases down the group be seen?
In the reactions of halogens with halide ions in solution where the more reactive halogen will displace the less reactive halogen from the solution
Why can’t the oxidising ability of fluorine be shown in the reaction of halogens with halide ions in solution?
F2 reacts with water so cannot be investigated this way
What is the difference between a halide and a halogen in terms of how they react?
Halogens are reduced; halides are oxidised
What does ‘the reducing ability of the halides’ mean?
The ability to cause other atoms to gain electrons
What happens to the reducing ability of the halides down group 7?
It increases
Why does the reducing ability of the halides increase down group 7?
• larger halide ion so easier to donate electrons • outermost electrons further from attraction of nucleus and more shielded by outer electrons • therefore attraction for the outermost electrons → weaker
What are the observations when a solid metal chloride is added to sulphuric acid?
White misty fume
What are the observations when a solid metal bromide is added to sulphuric acid?
• white misty fume • orange/brown fume • sodium dichromate paper → green
What are the observations when a solid metal iodide is added to sulphric acid?
• white misty fume • purple fumes • sodium dichromate paper → green • yellow solid • rotten egg smell or lead ethanoate paper → black in presence of H₂S
What is the product when sulphuric acid has been added to a solid metal chloride?
HCl
What are the products when sulphuric acid has been added to a solid metal bromide?
• HBr • Br₂ • SO₂
What are the products when sulphuric acid has been added to a solid metal iodide?
• HI • I₂ • SO₂ • S • H₂S