4.2 Group 7 Flashcards
What are halogens?
Halogens (group 7 elements) are covalently bonded, simple molecular substance
What are property trends of halogens?
-All are diatomic
-Colours get darker down the group
-MP/BP increases down the group
What colour and state is Fluorine?
Very pale yellow (g)
What colour and state is Chlorine?
Pale green (g)
What colour and state is Bromine?
Brown (l)- Volatile, releases brown fumes
What colour and state is Iodine?
Dark grey (s)- Sublimes, releases purple fumes
What colour and state is Astatine?
Black (s)
What happens when halogens react with metals?
Form ionic compounds
The reaction between sodium and chlorine:
2Na(s) + Cl2(g) –> 2NaCl(s)
-In this reaction, the outer-shell electrons from the metal are transferred to the halogen:
This is a redox reaction because:
* Na loses electrons = oxidised
* Cl gains electrons = reduced
The Cl also changes its name:
* Chlorine atom → Chloride ion
* Halogen → Halide
What is the reactivity trend going down Group 7?
-Halogens get less reactive down the group
Why does gaining an electron become less easy as you go down the halogen group?
- Atoms have more electron shells
- The extra electron is further from the nucleus
- So its attraction to the nucleus is weaker
What is the test for chlorine?
- Damp blue litmus paper → turns white
-This is because the chlorine acts as a bleaching agent, so it removes the colour from the paper
What type of reaction is halogen displacement reactions?
Halogen displacement reactions are all redox reactions.
What happens in the reaction between chlorine and potassium bromide?
-The more reactive halogen atom steals an electron from the halide ion in the salt
-The Cl atoms in Cl2 each take an electron from a Br− ion:
REDOX REACTION:
* Cl (in Cl2) gains an electron = reduced
* Br− loses an electron = oxidised
What happens to the boiling points of the halogens as you go down the group?
Increases
