Learning Objectives

• Understand the properties of Group 2 elements.
• Explain the trends in the atomic and physical properties within the group.
• Describe the reactivity and uses of Group 2 elements.
• Analyze the compounds formed by Group 2 elements.

Introduction to Group 2 Elements

• Group 2 elements are also known as alkaline earth metals.
• They include the elements beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
• These elements are found in the second column of the periodic table.

Atomic and Physical Properties

• Increasing atomic number from top to bottom: greater atomic radius.
• Smaller atomic size compared to Group 1 elements.
• Low ionization energies.
• Low electronegativity.
• Formation of 2+ cations.

Reactivity of Group 2 Elements

• Group 2 elements are highly reactive but less reactive than Group 1 elements.
• Reactivity increases from top to bottom of the group.
• Reactivity is due to low ionization energies, which allow the loss of two electrons to form a 2+ cation.
• React with oxygen to form oxides.

Uses of Group 2 Elements

1. Beryllium:
   • Used in the aerospace industry for its lightweight and high-strength properties.
   • Used as a moderator for nuclear reactors.

2. Magnesium:
   • Used in alloys, such as aluminum-magnesium alloy, for improved strength and corrosion resistance.
   • Used in fireworks to produce brilliant white light.

3. Calcium:
   • Essential for the strength and structure of bones and teeth.
   • Used as a reducing agent in the extraction of metals from their ores.

Compounds of Group 2 Elements

• Group 2 elements form compounds with various elements.
• Examples include:
  • Magnesium oxide (MgO): Used as a refractory material and in the production of cement.
  • Calcium carbonate (CaCO3): Found in limestone and used in the manufacturing of cement and as a dietary supplement.
  • Barium sulfate (BaSO4): Used in medical imaging as a contrast agent.

Trends in Melting and Boiling Points

• Melting and boiling points generally decrease down the group.
• This trend is due to:
  • Increasing atomic size.
  • Weaker metallic bonding.

Example: Melting and Boiling Points

Element | Melting Point (°C) | Boiling Point (°C) |-| Beryllium | 1287 | 2469 Magnesium | 650 | 1090 Calcium | 842 | 1492 Strontium | 769 | 1384 Barium | 727 | 1870

Equations for Reactions of Group 2 Elements

1. Reaction with Oxygen:
   • Example: 2Mg + O2 → 2MgO

2. Reaction with Water:
   • Example: Ca + 2H2O → Ca(OH)2 + H2

3. Reaction with Halogens:
   • Example: Ba + Cl2 → BaCl2

4. Reaction with Acids:
   • Example: Mg + 2HCl → MgCl2 + H2

5. Reaction with Sulfur:
   • Example: Sr + S → SrS

Properties of Group 2 Elements

• Group 2 elements have a general electron configuration of [noble gas] ns2.
• They have a silvery-white appearance.
• Relatively low densities and melting points compared to transition metals.
• Good conductors of heat and electricity.
• Form white compounds.
• Have a strong affinity for oxygen, forming oxides.

Atomic and Ionic Radii

• Atomic radii increase down the group.
• This is due to the addition of new electron shells.
• Ionic radii also increase down the group.
• Stronger attraction between the positive nucleus and the outer electrons results in a smaller atomic size.

Ionization Energies

• Ionization energy decreases down the group.
• The outermost electron in Group 2 elements is in an s-orbital, shielded from the nucleus by inner electrons.
• This makes removal of the outermost electron easier down the group.
• Lower ionization energies result in higher reactivity.

Reactivity with Water

• Group 2 elements react with water to form metal hydroxides and hydrogen gas.
• Example: Ca + 2H2O → Ca(OH)2 + H2
• The reaction becomes more vigorous down the group.
• Magnesium reacts slowly with cold water, beryllium does not react with water.

Reactivity with Oxygen

• Group 2 elements react with oxygen to form metal oxides.
• Example: 2Mg + O2 → 2MgO
• The reactivity with oxygen increases down the group.
• Beryllium does not readily form an oxide layer due to its strong affinity for oxygen.

Reactivity with Halogens

• Group 2 elements react with halogens to form metal halides.
• Example: Ba + Cl2 → BaCl2
• The reactivity increases down the group.
• Beryllium does not readily form halides due to its small size and high ionization energy.

Reactivity with Acids

• Group 2 elements react with acids to liberate hydrogen gas and form metal salts.
• Example: Mg + 2HCl → MgCl2 + H2
• The reactivity increases down the group.
• Beryllium does not react with acids due to its passive oxide layer.

Compounds of Group 2 Elements

• Group 2 elements form a wide range of compounds.
• Common compounds include oxides, hydroxides, carbonates, and sulfates.
• Examples:
  • Magnesium hydroxide (Mg(OH)2): Used as an antacid to neutralize excess stomach acid.
  • Calcium carbonate (CaCO3): Found in limestone and serves as a building material.

Uses of Group 2 Compounds

• Compounds of Group 2 elements find applications in various industries.
• Examples:
  • Barium sulfate (BaSO4): Used as a contrast agent in X-ray imaging.
  • Magnesium sulfate (MgSO4): Used in agriculture as a fertilizer.
  • Calcium hydroxide (Ca(OH)2): Used in the production of cement and as a flocculant in water treatment.

Summary

• Group 2 elements are also known as alkaline earth metals.
• They have similar atomic and physical properties, but reactivity increases down the group.
• Group 2 elements react with water, oxygen, halogens, and acids to form various compounds.
• They find uses in a wide range of industries, from construction to medicine.

Trends in Solubility of Group 2 Compounds

• Group 2 hydroxides and sulfates become less soluble down the group.
• Solubility of compounds decrease due to increased lattice energy.
• Example: Solubility of alkaline earth metal sulfates in water decreases in the order: Ba > Sr > Ca > Mg.

Trends in Thermal Stability of Group 2 Compounds

• Group 2 carbonates and nitrates become less thermally stable down the group.
• Decomposition of compounds is driven by the formation of more stable products.
• Example: Thermal decomposition of Group 2 carbonates forms metal oxides and carbon dioxide gas.

Flame Test Colors of Group 2 Elements

• Each Group 2 element gives off a characteristic flame color.
• Beryllium: No characteristic flame color.
• Magnesium: Brilliant white flame.
• Calcium: Brick red flame.
• Strontium: Crimson red flame.
• Barium: Pale green flame.

Biological Significance of Calcium and Magnesium

• Calcium: Essential for muscle contraction, nerve function, and blood clotting.
• Magnesium: Plays a crucial role in energy metabolism and enzyme function.
• Adequate intake of these elements is crucial for healthy bodily functions.

Aqueous Chemistry of Group 2 Elements

• Group 2 hydroxides are weakly basic and dissolve in water to form alkaline solutions.
• Example: Mg(OH)2(aq) + 2H2O(l) → Mg(OH)2(aq) + 2OH-(aq)
• Group 2 carbonates react with acids to form carbon dioxide gas, water, and a metal salt.
• Example: CaCO3(s) + 2HCl(aq) → CO2(g) + H2O(l) + CaCl2(aq)

Industrial Uses of Calcium

• Calcium compounds find applications in various industries.
• Calcium oxide (CaO), known as quicklime, is used in cement production and as a desiccant.
• Calcium carbonate (CaCO3) is used in the manufacturing of paper, plastics, and paints.
• Calcium hydroxide (Ca(OH)2), also known as slaked lime, is used in water treatment and as a pH adjuster in food products.

Industrial Uses of Magnesium

• Magnesium and its alloys are used extensively in the automotive and aerospace industries.
• Magnesium alloys are lightweight and exhibit good strength-to-weight ratios.
• Magnesium is used in the production of flares, fireworks, and photography flashbulbs.
• Magnesium sulfate (MgSO4) is used in medical applications, such as Epsom salts and as a magnesium supplement.

Environmental Impacts of Group 2 Elements

• Group 2 elements and their compounds can have both positive and negative environmental impacts.
• Positive: Use of magnesium alloys in vehicles reduces weight and fuel consumption.
• Negative: Improper disposal of Group 2 compounds can lead to water pollution and toxicity to aquatic organisms.
• Proper handling and disposal is necessary to minimize environmental impacts.

Summary

• Group 2 elements, or alkaline earth metals, have similar properties and trends.
• Reactivity and solubility of compounds increase down the group.
• Group 2 elements have important biological roles and find applications in various industries.
• Understanding the properties and compounds of Group 2 elements is essential in chemistry and many other fields.