Group 7 Flashcards
What group are the halogens in?
Group 7 (Group 17 in modern periodic tables).
How many electrons do halogens have in their outer shell?
Seven electrons.
Why are halogens considered highly reactive?
Because they have seven electrons in their outer shell and are close to achieving a full octet.
What is unique about astatine?
It is an artificially produced radioactive element.
What is the half-life of astatine’s most stable isotope?
8.5 hours.
In what minerals is fluorine typically found?
Fluorspar (CaF₂) and cryolite (Na₃AlF₆).
Where is chlorine most commonly found in nature?
Chlorine occurs chemically combined as sodium chloride in sea water, underground deposits (rock salt), and salt flats.
What are compounds formed between halogens and metals called?
Metal halides
What type of bond exists in halogen diatomic molecules, and how does it form?
A covalent bond, which forms when each halogen atom shares one electron to complete their outer shells.
Give an example of a halogen diatomic molecule and its representation.
Chlorine gas, represented as Cl₂.
What causes van der Waals forces between halogen molecules?
Temporary dipoles that form due to the changing electron distribution in atoms or molecules.
How do temporary dipoles affect adjacent molecules?
They induce dipoles in adjacent molecules, leading to attraction between the molecules.
Why are van der Waals forces important in halogen boiling points?
The strength of these forces determines how much energy is needed to separate the molecules and turn the substance into a gas.
What is the relationship between the number of electrons in a molecule and the strength of van der Waals forces?
More electrons lead to stronger van der Waals forces because the electron cloud is larger and more easily distorted.
Why do larger halogen atoms have stronger van der Waals forces?
Their larger electron clouds increase the likelihood of significant temporary dipoles.
Explain why fluorine has the lowest boiling point among halogens.
Fluorine atoms have only 9 electrons, resulting in weak van der Waals forces that require little energy to break.
What is the boiling point of chlorine, and why is it higher than fluorine’s?
Chlorine’s boiling point is -35 °C because it has 17 electrons, resulting in stronger van der Waals forces compared to fluorine.
What is the boiling point of chlorine, and why is it higher than fluorine’s?
Chlorine’s boiling point is -35 °C because it has 17 electrons, resulting in stronger van der Waals forces compared to fluorine.
How does the trend in boiling points continue from bromine to iodine?
Boiling points increase because bromine and iodine have more electrons, leading to even stronger van der Waals forces.
What happens to halogen molecules during boiling?
Energy from the surroundings is used to break the van der Waals forces, allowing the molecules to separate and enter the gas phase.
Arrange the boiling points of fluorine, chlorine, bromine, and iodine in increasing order.
Fluorine (-188 °C) < Chlorine (-35 °C) < Bromine (58.8 °C) < Iodine (184.4 °C).
Why does the boiling point trend down Group 7 align with the increase in atomic number?
As atomic number increases, halogens have more electrons, leading to stronger van der Waals forces and higher boiling points.
What is the key energy requirement for halogens to transition from liquid to gas?
Enough energy must be supplied to overcome the intermolecular van der Waals forces.
How does the size of a halogen molecule affect its boiling point?
Larger molecules have stronger intermolecular forces, requiring more energy to break and leading to higher boiling points.
What are the intermolecular forces between halogen molecules called?
Van der Waals forces.
How are temporary dipoles formed in halogen molecules?
Temporary dipoles form when the electron distribution in a molecule or atom changes, causing one end to be more negative and the other less negative.
What happens when a temporary dipole forms in a molecule?
It induces a temporary dipole in an adjacent molecule, and the intermolecular forces attract them to each other.
How does the number of electrons affect van der Waals forces?
The more electrons an atom or molecule has, the stronger the van der Waals forces
Why are van der Waals forces stronger in larger atoms or molecules?
Because their electron clouds are more easily distorted and extend further from the nucleus
Why does the boiling point of halogens increase down the group?
The number of electrons increases down the group, strengthening van der Waals forces and requiring more energy to break them.
What is the boiling point of fluorine, and why is it so low?
Fluorine has a boiling point of -188 °C because it has only 9 electrons, resulting in very weak van der Waals forces.
How does the boiling point of chlorine compare to fluorine, and why?
Chlorine has a higher boiling point of -35 °C because it has 17 electrons, creating stronger van der Waals forces
How do bromine and iodine compare in boiling points to fluorine and chlorine?
Bromine and iodine have progressively higher boiling points because their larger number of electrons creates stronger van der Waals forces, requiring more energy to break.
What types of compounds do halogens form?
Halogens form compounds with covalent molecules (e.g., hydrogen chloride gas) or ionic compounds (e.g., halide salts such as sodium chloride).
What are halides?
Halides are compounds made from halogen atoms and atoms of another element, often forming salts that are ionically bonded
Why are halogens good oxidising agents?
Halogen atoms readily accept electrons, making them strong oxidising agents
What is the trend in oxidising power down the halogen group?
The oxidising power decreases down the group:
F₂ > Cl₂ > Br₂ > I₂
Why is fluorine not used in laboratory experiments?
Fluorine is the most reactive and hazardous element known. It requires specialized equipment to handle safely
What is a displacement reaction involving halogens?
It is a reaction in which a more reactive halogen displaces a less reactive halogen from a solution of its halide ions
Write the general equation for a displacement reaction between halogens and halide ions.
X₂ (aq) + 2Y⁻ (aq) → 2X⁻ (aq) + Y₂ (aq)
(Where X is the more reactive halogen and Y is the less reactive halogen.)
What happens when chlorine is added to potassium bromide solution?
A yellow-orange solution of bromine forms:
Cl₂ (aq) + 2KBr (aq) → 2KCl (aq) + Br₂ (aq)
or
Cl₂ (aq) + 2Br⁻ (aq) → 2Cl⁻ (aq) + Br₂ (aq)
Why does chlorine displace bromine from potassium bromide?
Chlorine is a stronger oxidising agent than bromine and withdraws an electron from bromide ions, forming bromine molecules.
What is the visual change in the reaction between chlorine and potassium bromide?
The solution turns yellow-orange due to the formation of bromine.
What happens when bromine is added to potassium iodide solution?
A brown solution of iodine forms:
Br₂ (aq) + 2KI (aq) → 2KBr (aq) + I₂ (aq)
or
Br₂ (aq) + 2I⁻ (aq) → 2Br⁻ (aq) + I₂ (aq)
What are the oxidation and reduction half-equations for the reaction between chlorine and bromide ions?
Oxidation (bromine):
2Br⁻ → Br₂ + 2e⁻
Reduction (chlorine):
Cl₂ + 2e⁻ → 2Cl⁻
In the reaction between chlorine and bromide ions, which species is oxidised, and which is reduced?
- Bromide ions (Br⁻) are oxidised to bromine (Br₂).
- Chlorine (Cl₂) is reduced to chloride ions (Cl⁻
Why does bromine displace iodine from potassium iodide solution?
Bromine is a stronger oxidising agent than iodine and withdraws an electron from iodide ions, forming iodine molecules.
What are the redox half-equations for the reaction between bromine and iodide ions?
Oxidation (iodine):
2I⁻ → I₂ + 2e⁻
Reduction (bromine):
Br₂ + 2e⁻ → 2Br⁻
What is the visual change when bromine reacts with potassium iodide?
The solution turns brown due to the formation of iodine.
Which halogens can displace iodine from its halide solution?
Both chlorine and bromine can displace iodine because they are stronger oxidising agents.
What determines whether a halogen will displace another halogen in a halide solution?
A halogen higher up in the group (stronger oxidising agent) will displace a halogen lower in the group (weaker oxidising agent) from its halide solution.
Summarise the reactivity trend of halogens in displacement reactions.
Reactivity order:
Fluorine > Chlorine > Bromine > Iodine
A more reactive halogen displaces a less reactive halogen from its halide.
Why does the oxidising power of halogens decrease down the group?
Down the group, the atomic size increases, and the outer electrons are farther from the nucleus, reducing the attraction for electrons and making it harder to accept them
Why is fluorine the strongest oxidising agent?
Fluorine has the smallest atomic radius and highest electronegativity, making it extremely effective at attracting electrons.
Why is fluorine excluded from laboratory displacement reactions?
Fluorine is highly reactive and dangerous, requiring specialized equipment to handle safely.
Why is fluorine excluded from laboratory displacement reactions?
Fluorine is highly reactive and dangerous, requiring specialized equipment to handle safely.
How are metal halides formed, and what type of bonding do they exhibit?
Metal halides form when halogens react with Group 1 and Group 2 metals. The bonding is ionic, and the compounds have giant lattice structures consisting of metal ions and halide ions.
What is the electron configuration of a chloride ion (Cl⁻)?
The chloride ion has the same electron configuration as an argon atom, achieving a noble gas electronic configuration
Why can halide ions act as reducing agents?
Halide ions can transfer electrons and be oxidised to halogens, making them reducing agents
What is the trend in the reducing ability of halide ions down Group 7?
The reducing ability of halide ions increases down the group.
What role does concentrated sulfuric acid (H₂SO₄) play in its reaction with sodium halides?
H₂SO₄ acts as an acid, donating H⁺ ions to the halide ions, producing hydrogen halides (e.g., HCl, HBr, HI).
Write the reaction between NaCl and concentrated H₂SO₄.?
NaCl (s) + H₂SO₄ (aq) → HCl (g) + NaHSO₄ (aq)
Is the reaction between NaCl and H₂SO₄ a redox reaction?
No, there is no change in oxidation states, so it is not a redox reaction
What is observed during this reaction?
A colourless gas (HCl) evolves, and a colourless solution forms
Write the initial reaction between NaBr and concentrated H₂SO₄.
NaBr (s) + H₂SO₄ (aq) → HBr (g) + NaHSO₄ (aq)
Is the initial reaction between NaBr and H₂SO₄ a redox reaction?
No, there is no change in oxidation states in the initial reaction.
What secondary reaction occurs with HBr?
2HBr (g) + H₂SO₄ (aq) → Br₂ (g) + SO₂ (g) + 2H₂O (l)
What changes in oxidation states occur during the secondary reaction?
Bromine (Br⁻) is oxidised from -1 to 0 in Br₂.
Sulfur is reduced from +6 in H₂SO₄ to +4 in SO₂
What are the observations in this reaction?
Bromine is seen as a brown-orange liquid, and the colourless sulfur dioxide gas has a pungent odour
Write the initial reaction between NaI and concentrated H₂SO₄.
NaI (s) + H₂SO₄ (aq) → HI (g) + NaHSO₄ (aq)
What secondary reactions occur with HI?
- 2HI (g) + H₂SO₄ (aq) → I₂ (g) + SO₂ (g) + 2H₂O (l)
- 6HI (g) + H₂SO₄ (aq) → 3I₂ (g) + S (s) + 4H₂O (l)
- 8HI (g) + H₂SO₄ (aq) → 4I₂ (g) + H₂S (g) + 4H₂O (l)
What are the oxidation and reduction changes in these reactions?
Oxidation: I⁻ changes from -1 to 0 in I₂.
Reduction (varying products):
Sulfur changes from +6 in H₂SO₄ to: +4 in SO₂.
0 in S. -2 in H₂S
What are the observations for these reactions?
• Purple iodine vapour (I₂) is seen.
• Sulfur dioxide (SO₂) is colourless with a pungent odour.
• Sulfur (S) appears as a pale yellow solid, though it may be difficult to see in the reaction mixture.
• Hydrogen sulfide (H₂S) is a colourless gas with a rotten egg smell.
How do the reactions of halides with concentrated H₂SO₄ illustrate trends in reducing power?
The reducing power of halide ions increases down the group:
Cl⁻ < Br⁻ < I⁻.
Why does the reducing ability of halide ions increase down the group?
Down the group, halide ions have a larger atomic radius and weaker attraction between the outer electrons and the nucleus, making it easier to lose electrons.
What states are hydrogen halides in at room temperature?
All hydrogen halides are gases at room temperature
What states are hydrogen halides in at room temperature?
All hydrogen halides are gases at room temperature
Why are fluorides and chlorides excluded from certain reactions with concentrated sulfuric acid?
Hydrogen fluoride (HF) and hydrogen chloride (HCl) do not reduce sulfuric acid and therefore do not undergo further reactions like other hydrogen halides. Sodium fluoride (NaF) reacts similarly to sodium chloride (NaCl)
What happens when hydrogen bromide (HBr) reacts with concentrated sulfuric acid?
• Hydrogen bromide reduces the sulfur in sulfuric acid (H₂SO₄) to sulfur dioxide (SO₂).
• Bromide ions (Br⁻) are oxidised to bromine (Br₂).
What products are formed in the reaction between hydrogen bromide and sulfuric acid?
• Sulfur dioxide (SO₂) is produced as sulfur is reduced.
• Bromine (Br₂) is produced as bromide ions (Br⁻) are oxidised
What happens when hydrogen iodide (HI) reacts with concentrated sulfuric acid?
• Hydrogen iodide reduces sulfur in sulfuric acid to mainly hydrogen sulfide (H₂S).
• Small amounts of sulfur dioxide (SO₂) and sulfur (S) are also produced.
• Iodide ions (I⁻) are oxidised to iodine (I₂)
What products are formed in the reaction between hydrogen iodide and sulfuric acid?
• Hydrogen sulfide (H₂S), a gas with a rotten egg smell.
• Sulfur dioxide (SO₂), a colourless gas with a pungent odour.
• Sulfur (S), a pale yellow solid.
• Iodine (I₂), a purple vapour
What is the trend in the reducing ability of halide ions?
The reducing ability increases down Group 7, in this order:
F⁻ < Cl⁻ < Br⁻ < I⁻.
Why is hydrogen iodide a stronger reducing agent than hydrogen bromide, and why is hydrogen bromide a stronger reducing agent than hydrogen chloride?
• Hydrogen iodide (HI) is a stronger reducing agent than hydrogen bromide because iodide ions (I⁻) are larger and have weaker bonds, making them more likely to lose electrons.
• Hydrogen bromide (HBr) is a stronger reducing agent than hydrogen chloride (HCl) for similar reasons, with bromide ions (Br⁻) being larger and more easily oxidised than chloride ions (Cl⁻).
Summarise the trend in the reducing power of halide ions.
The reducing power of halide ions increases down the group, with the order:
F⁻ < Cl⁻ < Br⁻ < I⁻.
What is the purpose of adding silver nitrate to halide ions in solution?
To identify halide ions through precipitation reactions, where silver halides form precipitates of different colors.
What colors of precipitates do halides form with silver nitrate?
• Chloride (Cl⁻): White precipitate
• Bromide (Br⁻): Cream precipitate
• Iodide (I⁻): Yellow precipitate
• Fluoride (F⁻): No precipitate (AgF is water-soluble)
Why is silver nitrate acidified with dilute nitric acid?
To prevent the formation of precipitates from other ions, such as carbonate ions.
How do silver halides dissolve in ammonia?
• Silver chloride (AgCl): Dissolves in dilute ammonia.
• Silver bromide (AgBr): Dissolves in concentrated ammonia.
• Silver iodide (AgI): Does not dissolve in ammonia
Why is chlorine added to water during treatment?
To disinfect the water by killing bacteria and viruses.
What is the chemical reaction of chlorine with water during disinfection?
Cl2(aq) + H2O(l) (reversible arrow) HOCl(aq) + HCl(aq)
(Hypochlorous acid forms, disrupting cell membranes of bacteria and killing them.)
What happens when chlorine reacts with water?
Chlorine undergoes disproportionation, where it is simultaneously oxidized and reduced:
Cl2 + H2O (Reversible arrow) HOCl + HCl
How does chlorine react in sunlight?
Chloric(I) acid (HOCl) decomposes to form hydrochloric acid and oxygen:
2HOCl(aq) —> 2HCl(aq) + O2(g)
What is the reaction of chlorine with cold, dilute sodium hydroxide?
Cl2(g) + 2NaOH(aq) —> NaClO(aq) + NaCl(aq) + H2O(l)
(Sodium chlorate(I), used as bleach, is formed.)
What happens when chlorine reacts with hot, concentrated sodium hydroxide?
3Cl2(g) + 6NaOH(aq) —> NaClO3(aq) + 5NaCl(aq) + 3H2O(l)
(Sodium chlorate(V), used as a weed killer, is formed.)
What are some environmental concerns associated with chlorine use?
• Formation of dioxins and chlorofluorocarbons (CFCs), which cause skin conditions and contribute to ozone depletion.
• Residual chlorine in waste materials.
What happens to damp litmus paper when exposed to chlorine gas?
The litmus paper turns red (due to acidic conditions from HCl) and then is bleached white (due to chlorine’s oxidizing properties).
