11. Group 17 Flashcards
What are the colours and states of fluorine, chlorine, bromine and iodine at room temperature?
Fluorine- pale yellow gas
Chlorine- green/ yellow gas
Bromine- orange/brown liquid
Iodine- grey/ black solid
What are the characteristics of a volatile substance?
It will have a low melting and boiling point
Explain the trend of volatility down the group 17?
It decreases down the group because as you go down the group the atomic size increases as an addition electron is added. The London dispersion forces that exist between increase in strength as the atomic size increases therefore making it harder to break them as you go down.
What explains the melting and boiling point trends down the group 17 elements?
The more electrons there are in a molecule the greater the instantaneous dipole-induced dipole forces. So the larger the molecule the stronger the van der waals forces between molecules. So as you go down the group it gets more difficult to separate the molecules
What is thermal stability?
How well a substance can resist breaking down when heated
Explain the trend of thermal stability down group 17 hydrogen halides.
It decreases down the group.
As you go down the group the atomic radius of the halogens increases causing the bond length between hydrogen and halogen to increase. Longer bonds are generally weaker meaning less energy is required to break them.
Explain the bond strength down group 17 elements.
As you go down the group, the atomic radius increases, which makes it harder for the atoms to form strong covalent bonds. The bond length also increases as you go down the group, the longer the bond the weaker it is because the nuclei of the bonded atoms are farther apart.
Explain why the oxidizing power of the halogens decreases going down the group.
As you go down the group, the decreasing electronegativity makes the halogens less able to attract electrons, reducing their oxidizing ability.
Explain why the electronegativity decreases down group 17.
As the number of electron shells increases down the group, the inner electrons create a shielding effect, which reduces the effective nuclear charge. This shielding weakens the nucleus’ pull on the bonding electrons, resulting in a lower electronegativity as you move down the group.
Explain why the hydrogen halides decrease in thermal stability down group 17.
Down the group the atomic radius of the halogens increases. The overlap of its outer shell with a hydrogen atom therefore gives it a longer bond length, the longer the bond the weaker it is and the less energy required to break it.
Explain the trend of halide ions as reducing agents down the group 17.
The reducing power of the halide ions increases going down the group. As you go down the group, the halide ions become larger, with less tightly held outer electrons, which makes them more likely to donate electrons.
How can halide ions be identified in an unknown solution?
By dissolving the solution in nitric acid and then adding a silver nitrate solution followed by ammonia solution.
Explain how to determine which specific halide ion is in a solution.
Add dilute then concentrated ammonia to the silver halide solution.
If the ppt dissolves in dilute ammonia the unknown halide is chloride.
If the ppt does not dissolve in dilute but in concentrated ammonia the unknown halide is bromide.
If the ppt does not dissolve in dilute nor concentrated ammonia the unknown halide is iodide.
What is the color of chloride ion in a silver halide solution
White
What is the color of bromide ion in a silver halide solution
Cream
What is the color of iodide ion in a silver halide solution
Pale yellow
What is the equation for the reaction of sodium chloride ions with concentrated sulfuric acid? And what is observed
H2SO4 (l) + NaCl(s) → HCl(g) + NaHSO4 (s)
HCl gas produced is seen as white fumes.
What are the equations for the reaction of sodium bromide ions with concentrated sulfuric acid? And what is observed?
H2SO4 (l) + NaBr(s) → HBr(g) + NaHSO4 (s)
- The concentrated sulfuric acid oxidizes HBr which decomposes into bromine and hydrogen gas.
2HBr(g) + H2SO4 (l) → Br (g) + SO2 (g) + 2H2O(l)
Bromine is seen as a reddish-brown gas.
What are the equations for the reaction of iodide ions with concentrated sulfuric acid? And what is observed?
- H2SO4 (l) + NaI (s) → HI (g) + NaHSO4 (s)
-hydrogen iodide decomposes the easiest. - The concentrated sulfuric acid oxidizes HI
2HI (g) + H2SO4 (l) → I2 (g) + SO2 (g) + 2H2O (l)
Iodine is seen as a purple vapor - Concentrated sulfuric acid oxidizes HI and is itself reduced to sulfur
6HI (g) + H2SO4 (l) → 3I2 (g) + S (s) + 4H2O (l)
Sulfur is seen as a yellow solid. - The concentrated sulfuric acid oxidises HI and is itself reduced to hydrogen sulfide:
8HI (g) + H2SO4 (l) → 4I2 (g) + H2S (s) + 4H2O (l)
Hydrogen sulfide has a strong smell of bad eggs
Describe the reaction of chlorine and water
It’s a disproportionate reaction
Cl2 (aq) + H2O ——> HCl (aq) + HClO (aq)
Dissociation of caloric acid in water
HClO(aq) → H+ (aq) + ClO- (aq)
