Group 7 Flashcards
(20 cards)
What are the Group 7 elements?
Fluorine (F2), chlorine (Cl2), bromine (Br2), iodine (I2), and astatine (At2).
What is the general electronic configuration of Group 7 elements?
[noble gas] ns2 np5.
What happens to atomic radius and electronegativity as you go down Group 7?
Atomic radius increases due to additional electron shells, and electronegativity decreases because the increased shielding reduces the nuclear attraction for bonding electrons.
What is the trend in boiling points down Group 7?
Boiling points increase due to stronger van der Waals forces as the size and mass of the molecules increase.
What are the physical states of the first four halogens at room temperature?
Fluorine: Pale yellow gas
Chlorine: Green gas
Bromine: Red-brown liquid
Iodine: Shiny grey solid (sublimes to a violet gas)
What is the trend in oxidizing power of halogens down the group?
Oxidizing power decreases because the larger atomic radius and increased shielding reduce the ability to attract electrons.
What is a displacement reaction involving halogens?
A more reactive halogen displaces a less reactive halogen from its compound.
Example: Cl2 + 2KI → 2KCl + I2
What is the trend in reducing power of halide ions down the group?
Reducing power increases because the larger ionic radius makes it easier to lose an electron.
What happens when halide ions react with concentrated sulfuric acid?
Chloride (Cl-): Produces HCl (steamy fumes).
Bromide (Br-): Produces HBr and SO2 (steamy fumes and choking gas).
Iodide (I-): Produces HI, SO2, S, and H2S (steamy fumes, choking gas, yellow solid, and rotten egg smell).
What is the test for halide ions?
Add dilute HNO3 and AgNO3. Precipitate colors:
Cl-: White (soluble in dilute NH3)
Br-: Cream (soluble in concentrated NH3)
I-: Yellow (insoluble in NH3)
How does chlorine react with water?
Cl2 + H2O ↔ HCl + HClO
This is a disproportionation reaction.
What is the reaction of chlorine with cold, dilute NaOH?
Cl2 + 2NaOH → NaCl + NaClO + H2O
This produces bleach (sodium chlorate(I)).
What is the use of chlorine in water treatment?
Chlorine kills bacteria by forming chloric(I) acid (HClO), which is an oxidizing agent.
Why is chlorine both beneficial and controversial in water treatment?
Beneficial: Kills harmful bacteria, making water safe to drink.
Controversial: Can form chlorinated hydrocarbons, which are carcinogenic.
What is the trend in bond enthalpy of halogen-halogen bonds?
Bond enthalpy decreases down the group because atomic size increases, weakening the bond.
What colors do Group 7-related cations produce in a flame test?
Group 7 elements themselves do not produce flame test colors, but related Group 1 and 2 cations show:
Lithium (Li+): Crimson red
Sodium (Na+): Yellow
Potassium (K+): Lilac
Calcium (Ca2+): Brick red
Strontium (Sr2+): Red
Barium (Ba2+): Pale green
What happens when sodium chloride reacts with concentrated sulfuric acid?
Reaction: NaCl + H2SO4 → HCl + NaHSO4
Observation: Steamy fumes of HCl.
Explanation: Chloride ions are weak reducing agents, so no further reaction occurs.
What happens when sodium bromide reacts with concentrated sulfuric acid?
Initial Reaction: NaBr + H2SO4 → HBr + NaHSO4 (produces steamy fumes of HBr).
Further Reaction: 2HBr + H2SO4 → Br2 + SO2 + 2H2O.
Observations: Steamy fumes of HBr, brown fumes of Br2, and choking gas (SO2).
Explanation: Bromide ions are stronger reducing agents than chloride ions, reducing H2SO4 to SO2.
What happens when sodium iodide reacts with concentrated sulfuric acid?
Initial Reaction: NaI + H2SO4 → HI + NaHSO4 (produces steamy fumes of HI).
Further Reactions:
2HI + H2SO4 → I2 + SO2 + 2H2O
6HI + SO2 →3I2 + H2S + 3H2O
Observations: Steamy fumes of HI, purple fumes or black solid (I2), choking gas (SO2), yellow solid (S), and rotten egg smell (H2S).
Explanation: Iodide ions are the strongest reducing agents, reducing H2SO4 to SO2, S, and H2S.
Why do halide ions react differently with concentrated sulfuric acid?
The difference lies in the reducing power of the halide ions, which increases down the group.
Chloride ions (Cl-) are poor reducing agents, so no further reduction of H2SO4 occurs.
Bromide ions (Br-) can reduce H2SO4 to SO2, and iodide ions (I-) reduce it further to S and H2S.
