1. Chapter 13 The s-Block Elements

2. Chapter 13: s-Block Elements
Introduction
Early chemical knowledge was mostly of a practical nature, a how-to of chemical processes
The periodic table provides an organizational scheme for a systematic study of the elements and their compounds
EOS
Hydrogen, helium, francium, and radium have certain characteristics that make them stand out from the s-block elements
Chapter 13: s-Block Elements

3. Chapter 13: s-Block Elements
Hydrogen
Because hydrogen atoms are the simplest of all the atoms, hydrogen has always been considered rather special
Hydrogen makes up 0.9% of the mass and 15.1% of the atoms in Earth’s crust, but makes up 89% of the atoms of the Sun, and 90% of all atoms in the universe as a whole
EOS
The most direct method of producing hydrogen is the decomposition of water
Chapter 13: s-Block Elements

4. Chapter 13: s-Block Elements
Electrolysis of Water
H2(g) forms at the negative electrode (cathode)
O2(g) forms at the positive electrode (anode)
EOS
Stoichiometry of gas produced is 2:1 (H2:O2)
WaterElectrolysis
Chapter 13: s-Block Elements

5. Developments Linked to Hydrogen
EOS
Chapter 13: s-Block Elements

6. Binary Compounds of Hydrogen
Hydrogen reacts with other nonmetals to form molecular compounds
When combined with metals forms a “hydride”
e.g., LiH, lithium hydride
Hydrogen reacts with the most active metals to form ionic hydrides, in which hydrogen exists as the hydride ion, H–
EOS
Ionic hydrides react with water to liberate H2(g)
Chapter 13: s-Block Elements

7. Chapter 13: s-Block Elements
Molecular Mass
When hydrides are formed from transition elements, the products, called metallic hydrides, retain some metallic properties such as electrical conductivity
EOS
Chapter 13: s-Block Elements

8. Chapter 13: s-Block Elements
Uses of Hydrogen
Nearly half the hydrogen gas produced is used in the manufacture of ammonia (NH3)
Another chemical manufacturing process that uses hydrogen is the synthesis of methanol, an industrial solvent
Liquid hydrogen is used as a rocket fuel
EOS
An oxyhydrogen welding torch using atomic hydrogen readily cuts through steel and can be used to melt tungsten, which has a melting point of about 3400 oC
Chapter 13: s-Block Elements

9. The Alkali Metals (Group IA)
The most active of the metals, those of Group 1A and the heavier members of Group 2A, displace H2(g) even from pure water
SodiumReaction
EOS
Chapter 13: s-Block Elements

10. Group 1A Properties and Trends
The alkali metals have two notable physical properties: they are all soft and have low melting points
When freshly cut, the alkali metals are bright and shiny—typical metallic properties. The metals quickly tarnish, however, as they react with oxygen in the air
EOS
Irregular trends suggest that factors are working against each other in determining a property (such as the density “discrepancies” between sodium and potassium)
Chapter 13: s-Block Elements

11. Chapter 13: s-Block Elements
Group 1A Properties
Flame tests are used to identify Gp 1A elements
FlameTests
EOS
Chapter 13: s-Block Elements

12. Diagonal Relationships
In some of its properties, lithium compounds resemble magnesium and its compounds
EOS
Chapter 13: s-Block Elements

13. The Special Case of Lithium
Lithium carbonate, fluoride, hydroxide, and phosphate are much less water-soluble than those of other alkali metals
Lithium is the only alkali metal that forms a nitride (Li3N)
When it burns in air, lithium forms a normal oxide (Li2O) rather than a peroxide or a superoxide
EOS
Lithium carbonate and lithium hydroxide decompose to form the oxide on heating, while other Group 1A carbonates and hydroxides are thermally stable
Chapter 13: s-Block Elements

14. Preparation of the Alkali Metals
To convert an alkali metal ion into an alkali metal atom, the ion must take on an electron—a process of reduction
Potassium was the first to be prepared by electrolysis
Liquid sodium is used as a heat transfer medium in some types of nuclear reactors and in automobile engine valves, and its vapor can be used in lamps for outdoor lighting
EOS
Lithium is used in lightweight electrical batteries of the type found in clocks and watches, hearing aids, and heart pacemakers
Chapter 13: s-Block Elements

15. Typical Alkali Metal Reactions
EOS
Chapter 13: s-Block Elements

16. Chemicals Produced from Sodium Chloride
EOS
Chapter 13: s-Block Elements

17. Preparation of Sodium Compounds from NaCl
EOS
Chapter 13: s-Block Elements

18. Chapter 13: s-Block Elements
The Solvay Process
EOS
Chapter 13: s-Block Elements

19. The Alkali Metals and Living Matter
Sodium ions are found primarily in fluids outside cells and potassium ions are abundant in fluids within cells
Because most alkali metal compounds are water soluble, many acidic drugs are administered in the form of their sodium or potassium salts
EOS
Lithium carbonate is used in medicine to level out the dangerous manic “highs” that occur in manic-depressive psychoses
Chapter 13: s-Block Elements

20. Group 2A Metal Properties
EOS
Chapter 13: s-Block Elements

21. Group 2A Properties and Trends
Group 2A shows the same general trends of increasing atomic and ionic sizes and decreasing ionization energies from top to bottom as Group 1A
The higher densities of the Group 2A metals are mainly a consequence of the large differences in atomic sizes
EOS
There is an interesting trend in the solubilities of the metal hydroxides of Group 2A in water: cation size , the interionic attractions  and the solubilities of the compounds in water increase
Chapter 13: s-Block Elements

22. Molecular Structure of BeCl2
Beryllium forms an sp hybrid set of orbitals
EOS
Chapter 13: s-Block Elements

23. Preparation of the Alkaline Earth Metals
Be: the mineral beryl (3 BeO·Al2O3·6 SiO2) is first converted to BeF2 which is reduced to beryllium using magnesium as the reducing agent
Ca: obtained by electrolysis of molten CaCl2
Sr and Ba: made by electrolysis or high-temperature reduction of their oxides using aluminum as the reducing agent
EOS
Mg is obtained by the electrolysis of molten MgCl2, in a process called The Dow Process
Chapter 13: s-Block Elements

24. Chapter 13: s-Block Elements
The Dow Process
EOS
Chapter 13: s-Block Elements

25. Uses of the Alkaline Earth Metals
Alloys of Be with other metals have many applications such as springs, clips, and lightweight structural materials
Mg has a lower density than any other structural metal and is an important metallurgical reducing agent. Mg is also used in batteries and fireworks
EOS
Ca is used to reduce the oxides or fluorides of less common metals to the free metals
Also forms alloys with aluminum, silicon, and lead
Chapter 13: s-Block Elements

26. Chapter 13: s-Block Elements
Compounds of Mg and Ca
Several magnesium compounds occur naturally, either in mineral form or in brines and include the carbonate, chloride, hydroxide, and sulfate
Limestone is a naturally occurring form of CaCO3, containing some clay and other impurities
EOS
Gypsum has the formula CaSO4·2 H2O. Another hydrate of calcium sulfate is plaster of paris which has the formula CaSO4 ·½ H2O and is obtained by heating gypsum
Chapter 13: s-Block Elements

27. Important Magnesium Compounds
EOS
Chapter 13: s-Block Elements

28. Group 2A Metals and Living Matter
Persons of average size have approximately 25 g of magnesium in their bodies: the recommended daily intake of magnesium for adults is 350 mg
Calcium is essential to all living matter. The human body typically contains from 1 to 1.5 kg of calcium
EOS
Barium has no known function in organisms; in fact, the Ba2+ ion is toxic
Chapter 13: s-Block Elements

29. Chapter 13: s-Block Elements
Water Applications
Hard water is groundwater that contains significant concentrations of ions from natural sources
If the primary anion is the HCO3–, the hardness is said to be temporary hardness, otherwise it is permanent hardness
EOS
Water softening can be accomplished through ion exchange, the process of exchanging undesirable ions for ions that are less objectionable by using synthetic resins called zeolites
Chapter 13: s-Block Elements

30. Chapter 13: s-Block Elements
Ion Exchange
EOS
Chapter 13: s-Block Elements

31. Chapter 13: s-Block Elements
Soaps and Detergents
A soap acts by dispersing grease and oil films into microscopic droplets
The droplets detach themselves from the surfaces being cleaned, become suspended in water, and are removed by rinsing
The alkali metal soaps are water soluble, the alkaline earth metal soaps are not
EOS
A soap can function well in hard water only after a part of it is used up to precipitate all the alkaline earth metal ions present
Chapter 13: s-Block Elements

32. Cleaning Action of a Soap
Hydrophilic portion
Hydrophobic portion
Water phase
EOS
Organic phase
Chapter 13: s-Block Elements

33. Chapter 13: s-Block Elements
Summary of Concepts
The main sources of H2 are the electrolysis of water, the water-gas reactions, and reforming of hydrocarbons
Of the s-block elements, the Group 1A metals have the largest atomic radii and lowest ionization energies
EOS
The Group 2A metals have smaller atomic radii and greater ionization energies than the Group 1A metals
Chapter 13: s-Block Elements

34. Chapter 13: s-Block Elements
Summary of Concepts
EOS
The slight dissolution of minerals in acidified rainwater introduces ions into groundwater. This dissolving action is responsible for natural caverns, limestone formations, and “hardness” in water
Chapter 13: s-Block Elements