3.2 Group 2 and Halogens for A-Level Chemistry (OCR B

What collective name is given to the elements in Group 2 of the Periodic Table?

Alkaline earth metals

Examples include Mg, Ca, Sr and Ba.

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What happens to atomic radius as you move down Group 2 from Mg to Ba?

Increases

Additional electron shells increase the size of the atoms.

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Fill in the blank:

The first ionisation energy of Group 2 elements generally _______ down the group.

decreases

Increased distance and shielding reduce attraction to the outer electron.

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True or False:

The reactivity of Group 2 metals increases down the group.

True

Lower ionisation energies make electron loss easier.

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What type of bonding holds atoms together in Group 2 metals?

Metallic bonding

Positive ions are surrounded by delocalised electrons in a lattice.

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True or False:

Magnesium reacts rapidly with cold water.

False

Magnesium reacts very slowly with cold water but reacts faster with steam.

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Fill in the blank:

Magnesium reacts with steam to produce magnesium _______ and hydrogen.

oxide

Mg + H₂O (steam) → MgO + H₂.

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What trend occurs in the solubility of Group 2 hydroxides down the group?

Increases

For example, Mg(OH)₂ is sparingly soluble while Ba(OH)₂ is much more soluble.

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True or False:

Magnesium hydroxide is used in medicine as an antacid.

True

It neutralises excess stomach acid.

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What agricultural substance is used to neutralise acidic soils?

Calcium hydroxide

It increases soil pH to improve crop growth.

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Fill in the blank:

The solubility of Group 2 _______ decreases down the group.

sulfates

BaSO₄ is insoluble in water.

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What reagent is used to test for sulfate ions in solution?

Acidified barium chloride

A white precipitate of BaSO₄ confirms sulfate ions.

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What property of magnesium hydroxide allows it to be used as an antacid?

It is sparingly soluble in water.

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How does melting point change down Group 2?

It generally decreases down the group.

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How is titanium extracted from TiCl₄ using magnesium?

TiCl₄ + 2Mg → Ti + 2MgCl₂

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Why does the melting point of Group 2 elements decrease down the group?

The ions get larger, so charge density decreases and metallic bonding becomes weaker.

Weaker electrostatic attraction between positive ions and delocalised electrons.

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What is the role of magnesium in extracting titanium from TiCl₄?

It acts as a reducing agent.

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Why are CaO or CaCO₃ used in flue gas treatment?

To remove SO₂ (a pollutant)

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What are the equations for removing SO₂ using CaO/CaCO₃?

CaO + SO₂ → CaSO₃
CaCO₃ + SO₂ → CaSO₃ + CO₂

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Why is SO₂ removed from flue gases?

To reduce acid rain and environmental damage.

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What is BaSO₄ used for in medicine?

Barium meal- lines the gut in X rays

It is insoluble so it does not release toxic Ba²⁺ ions, and it absorbs X-rays due to its high density, outlining the gut.

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What is the equation for the sulfate test using BaCl₂?

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

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Why is the solution acidified when testing for sulfate ions?

Study These Flashcards

To remove carbonate impurities that could also form a precipitate

What would happen if the solution was not acidified?

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Carbonate ions could form BaCO₃(s), giving a false positive.

What general **trend in electronegativity** occurs down **Group 7** from fluorine to iodine?

Decreases ## Footnote Increased atomic radius and shielding reduce the nucleus’ attraction for bonding electrons.

What happens to the **boiling point** of **halogens** as you move down Group 7?

Increases ## Footnote Larger molecules have stronger London dispersion forces.

# Fill in the blank: The increase in **boiling point** down the halogen group is due to stronger _\_\_\_\_\_\_ forces.

van der Waals ## Footnote These induced dipole–dipole forces increase with molecular size.

# True or False: **Chlorine** is a stronger **oxidising agent** than iodine.

True ## Footnote Oxidising ability decreases down the group.

What happens to the **oxidising ability** of **halogens** down Group 7?

Decreases ## Footnote Larger atoms gain electrons less easily.

# True or False: **Iodide ions** are stronger **reducing agents** than chloride ions.

True ## Footnote Reducing ability of halide ions increases down the group.

# Fill in the blank: In **displacement reactions**, a more reactive halogen will _\_\_\_\_\_\_ a less reactive halide from solution.

displace ## Footnote For example, Cl₂ displaces Br^- from solution.

What **reagent** is used to test for **halide ions** in aqueous solution?

Acidified silver nitrate ## Footnote It forms characteristic precipitates with halide ions.

# True or False: **Silver nitrate solution** is acidified to remove **interfering carbonate ions**.

True ## Footnote Nitric acid prevents false positives from other precipitates.

# Fill in the blank: A **white precipitate** formed with silver nitrate indicates the presence of _\_\_\_\_\_\_ ions.

chloride ## Footnote AgCl forms a white precipitate.

What happens when **dilute ammonia** is added to **silver chloride**?

Dissolves ## Footnote AgCl dissolves because it forms a soluble complex ion.

Which **silver halide** does not dissolve in **ammonia solution**?

Silver iodide ## Footnote AgI is the least soluble of the silver halides.

What **ions** are formed when **chlorine reacts with water** in the main equilibrium reaction?

Chloride and chlorate(I) ## Footnote Cl₂ + H₂O ⇌ Cl^- + ClO^- + H⁺.

What type of **ion** is **ClO⁻** formed when chlorine reacts with water?

Chlorate(I) ion ## Footnote Also known as the hypochlorite ion.

# Fill in the blank: When **chlorine dissolves in water**, it forms chloride ions and _\_\_\_\_\_\_ (I) ions.

chlorate ## Footnote These ions contribute to chlorine’s disinfectant properties.

# True or False: **Chlorine** can react with water to produce **oxygen and chloride ions**.

True ## Footnote An alternative reaction forms O₂ and HCl.

What is the **main use of chlorine** in **public water supplies**?

To kill bacteria. ## Footnote Chlorine kills bacteria and other microorganisms.

# True or False: The **health benefits** of **chlorinating drinking water** generally outweigh the risks.

True ## Footnote Chlorination has greatly reduced waterborne diseases.

# Fill in the blank: Chlorine reacts with **cold dilute sodium hydroxide** to form sodium chloride and sodium _\_\_\_\_\_\_ (I).

chlorate ## Footnote The product is sodium chlorate(I) (sodium hypochlorite).

What common **household chemical** contains **sodium chlorate(I)**?

Bleach ## Footnote Sodium hypochlorite is widely used as a disinfectant and bleaching agent.

# True or False: **Chlorate(I) ions** act as **oxidising agents** in disinfectants.

True ## Footnote They kill microbes by oxidising biological molecules.

Why is **chlorine** effective in **killing bacteria** in water treatment?

Strong oxidising agent ## Footnote It disrupts essential cellular components in microorganisms.

# Fill in the blank: In **water treatment**, chlorine is added because it kills harmful _\_\_\_\_\_\_.

microorganisms ## Footnote This prevents diseases such as cholera and typhoid.

What **societal factor** must be considered when adding chemicals like **chlorine to water supplies**?

Risk–benefit balance ## Footnote Decisions weigh health benefits against potential chemical risks.

Explain **why the electronegativity** of the halogens **decreases** going down the group

The number of electron shells increases down the group. This increases atomic radius and electron shielding. As a result, the nucleus has a weaker attraction for bonding electrons.

What is the colour of the **silver bromide precipitate**?

Cream

What is the colour of the **silver iodide precipitate**?

Yellow

How does **NaCl react with concentrated H₂SO₄**?

Forms HCl gas. This is an acid-base reaction only, no redox occurs.

How does **NaBr** react with concentrated **H₂SO₄**?

Forms **HBr** gas. **HBr** can be oxidized by **H₂SO₄** to produce **Br₂**. ## Footnote This occurs because **Br⁻** is a stronger reducing agent than **Cl⁻**.

How does **NaI** react with concentrated **H₂SO₄**?

Forms **HI** gas. **HI** is a strong reducing agent, leading to further reactions that can produce: * **I₂** (iodine) * **H₂S**, **SO₂**, or **S** (depending on conditions)

Why do **larger halide ions** have **stronger reducing ability**?

Larger ions (I⁻, Br⁻) have weaker hold on their electrons, making them more able to donate electrons → stronger reducing agents → more likely to reduce H₂SO₄

3.2 Group 2 and Halogens Flashcards

Predict reactivity and properties of Group 2 elements and halogens using trends in atomic structure and redox behavior. (55 cards)