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Questions and Answers
What happens to the atomic radius of group 7 elements as you move down the group?
What trend is observed in the reactivity of group 7 elements as you move down the group?
Which halogen is a gas at room temperature?
How does the boiling point of group 7 elements change as you move down the group?
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What is the nature of halide ions and their role in redox reactions?
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What is the effect of increased atomic radius on the ionization energy of group 7 elements?
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What trend is observed in the oxidizing power of the halogens as you move down the group?
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Which of the following statements about halogens is FALSE?
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What happens to the reducing power of halide ions as you move down the group?
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Which precipitate would form when reacting silver nitrate with chloride ions?
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In a disproportionation reaction involving chlorine and water, what are the products formed?
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What precipitate forms when silver nitrate reacts with bromide ions?
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How can you distinguish between the silver bromide and silver iodide precipitates?
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What is a key ingredient produced when chlorine reacts with cold, aqueous sodium hydroxide?
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What is the oxidation state change of chlorine in the disproportionation reaction when reacting with water?
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What risks are associated with using chlorine in water treatment processes?
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What color precipitate forms when Cl- ions react with AgNO3?
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Which ion is confirmed by fizzing when an acid like HCl is added?
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What is the color of the precipitate formed when BaCl2 reacts with sulfate ions?
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What observable change occurs when ammonium ions are tested with red litmus?
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Which Group 2 ion produces a brick red color in flame tests?
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Which of the following statements is true regarding the reaction of precipitates with concentrated ammonia (conc. NH3)?
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What visual change indicates the presence of hydroxide ions when tested with universal indicator?
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Which cation produces a pale green color in flame tests?
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What is the color of the precipitate formed when silver nitrate reacts with iodide ions?
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What occurs when dilute ammonia is added to the white precipitate formed from chloride ions and silver nitrate?
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Which of the following describes the effect of increased shielding on the reducing power of halide ions as atomic size increases?
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When chlorine reacts with cold water, which ions are produced?
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In the presence of concentrated ammonia, which precipitate formed from silver nitrate and bromide ions remains unchanged?
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What is a notable risk associated with using chlorine in water treatment processes?
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What happens when concentrated sodium hydroxide is mixed with chlorine?
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During the disproportionation reaction of chlorine with water, what changes in oxidation states occur?
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What trend is observed in the atomic radius of group 7 elements as you move down the group?
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Why does reactivity decrease among group 7 elements as you move down the group?
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Which of the following statements about ionisation energy in group 7 elements is correct?
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What is the reason for the increasing boiling points of group 7 elements down the group?
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How do halogens behave as oxidizing agents?
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What happens to the oxidizing power of halogens as you move down the group?
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What characterizes halide ions in terms of their reactivity?
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Which halogen is a solid state at room temperature?
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What color precipitate is formed when reacting silver nitrate with iodide ions?
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Which of the following ions indicates an alkaline solution by turning red litmus blue?
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What observable reaction occurs when carbonate ions are treated with hydrochloric acid (HCl)?
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What color does the flame turn when strontium (Sr^2+) ions are tested?
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What happens to silver chloride precipitate when concentrated ammonia (conc. NH3) is added?
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What is the visual indicator of the presence of ammonium ions using red litmus?
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Which of the following cations produces a pale green color during a flame test?
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What indicates the presence of sulfate ions when tested with BaCl2?
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Study Notes
Group 7: The Halogens
- Group 7 are the halogens, highly reactive non-metals
- Their atomic radius increases down the group due to the addition of electron shells
- Each element needs to gain an electron to form a 1- ion to achieve a full outer shell
- Reactivity decreases down the group as the atomic radius increases, meaning it becomes harder to attract an electron
- The first ionisation energy decreases down the group due to a greater atomic radius and increased shielding.
- Halogens are simple covalent molecules held together by van der waals forces
- The strength of these van der waals forces increases down the group, which requires more energy to overcome and results in a higher boiling point
- Fluorine is a gas at room temperature, whereas iodine is a solid
- Halogens are good oxidising agents as they accept electrons from the species being oxidised and are reduced.
- Their oxidising power decrease down the group as their ability to attract electrons decreases due to shielding and a greater atomic radius
- A halogen will displace any halide beneath it in the periodic table
- Halide ions are the negative ions formed from halogens
- They are good reducing agents which donate electrons to the species being reduced
- Their reducing power increases down the group as electrons are easier to lose from larger ions due to shielding and a larger atomic radius
- Halide ions react with sulfuric acid to form different products depending on how strong a reducing agent they are, with stronger reducing agents reacting further
- Acidfied silver nitrate is used to test for halide ions
- Silver nitrate reacts with halide ions to form coloured precipitates
- The colour of precipitate can be hard to distinguish, they can be further tested using ammonia
- Cl- with silver forms a white precipitate (AgCl) that dissolves in dilute and concentrated ammonia
- Br- with silver forms a cream precipitate (AgBr) that dissolves in concentrated ammonia only
- I- with silver forms a yellow precipitate (AgI) that doesn't dissolve in concentrated ammonia
- Chlorine reacts with cold water to produce chlorate(I) ions (ClO-) and chloride ions
- This is a disproportionation reaction as the chlorine is oxidised and reduced, with its oxidation state going from 0 to +1 and -1
- In the presence of UV light chlorine decomposes water to produce oxygen and hydrochloric acid
- Chlorine is reduced in this reaction
- Chlorine is used in water treatment to kill bacteria but it can be toxic
- Chlorine can be mixed with cold aqueous sodium hydroxide to produce sodium hypochlorite, a key ingredient in bleach
- Anions are tested using acidified silver nitrate and ammonia
- Anions (SO42-) are tested using BaCl2, which reacts to form a white precipitate
- Anions (OH-) can be identified with red litmus, which turns blue
- Anions (CO32-) can be identified by reacting with an acid which will cause fizzing and release CO2 gas
- The gas can be collected and bubbled through limewater, which will turn cloudy, confirming it as CO2
- Cations (Ca2+) can be identified with a flame test and will produce a brick red flame
- Cations (Sr2+) can be identified with a flame test and will produce a red flame
- Cations (Ba2+) can be identified with a flame test and will produce a pale green flame
- Cations (NH4+) can be identified with a red litmus test because they release ammonia gas which is a base, the litmus will turn from red to blue
- Cations (NH4+) can also be identified by adding NaOH, which will produce ammonia gas quickly
Group 7 Elements - The Halogens
- Group 7 elements are highly reactive non-metals that need to gain an electron to form a 1- ion and achieve a full outer shell of electrons.
- As you go down group 7, the atomic radius increases due to the addition of electron shells.
- Reactivity decreases down the group because the attraction of the nucleus weakens due to shielding making it harder for atoms to attract an electron.
- The first ionization energy of group 7 elements decrease down the group due to a greater atomic radius and increased amounts of shielding.
- Group 7 elements are simple covalent molecules held together by Van der Waals forces, which increase in strength as you go down the group. This means more energy is required to overcome the intermolecular forces resulting in a higher boiling point.
- Fluorine is a gas at room temperature, whereas iodine is a solid.
- Halogens act as strong oxidizing agents because they accept electrons from the species being oxidized and are reduced.
- Oxidizing power decreases down the group as their ability to attract electrons decreases due to shielding and a greater atomic radius.
- A halogen will displace any halide beneath it in the periodic table, meaning a higher halogen will displace a lower halogen.
Halide Ions
- Halide ions are the negative ions of halogens and act as good reducing agents.
- This is because they donate electrons to species being reduced and are themselves oxidized.
- Reducing power increases down the group as electrons are easier to lose from larger ions (due to shielding and larger atomic radius).
Silver Nitrate
- Acidified silver nitrate is used to test for halide ions as it reacts to form different colored precipitates depending on the ion present.
- The precipitates formed may not be clear to distinguish, so they can be tested further using ammonia.
Chlorine and Chlorate(I) ions
- Chlorine reacts with cold water to produce chlorate(I) ions (ClO-) and chloride ions.
- This is a disproportionation reaction because the chlorine is both oxidized and reduced. The oxidation state goes from zero to +1 and -1.
- In the presence of UV light, chlorine decomposes water to produce oxygen and hydrochloric acid. The chlorine is reduced in this reaction.
- Chlorine is used in water treatment processes, but it can be toxic.
- Chlorine can be mixed with cold, aqueous sodium hydroxide to produce sodium hypochlorite, which is a key ingredient in bleach.
Tests for Ions
- Halides can be tested using acidified silver nitrate and ammonia.
- Sulfates can be tested using BaCl2, which reacts to form a white precipitate.
- Hydroxides can be tested using red litmus paper (which turns blue) or a universal indicator (which turns blue-purple).
- Carbonates can be tested by adding acid (such as HCl), which will cause the substance to fizz (effervescence) and produce CO2 gas. This gas can be collected and bubbled through limewater, which will turn cloudy, confirming it as carbon dioxide.
Cations
- Calcium (Ca2+), Strontium (Sr2+), and Barium (Ba2+) ions can be identified using flame tests.
- Ammonium (NH4+) ions can be identified by holding red litmus paper over the substance being tested. If ammonium ions are present, the litmus paper will turn blue. Alternatively, NaOH can be added to produce ammonia gas faster.
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Description
Test your knowledge on Group 7, the halogens, and their properties. This quiz covers their reactivity, atomic radii, and ionization energies, along with their behavior as oxidizing agents. Understand the trends within this group of highly reactive non-metals.
