Chapter Twenty

1
Chapter Twenty

• The s-Block Elements

2
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.
• Four of the 14 elements that comprise the s-block
  elements are somewhat unusual cases, although not
  all for the same reason.
• Hydrogen, Helium, Francium, and Radium have
  certain characteristics that make them stand out
  from the s-block elements.

3
alkali metals
halogens
alkaline earth
main group elements
18
1
p block
2
13
16
17
15
14
H
He
transition metals d block
2p
Li
B
C
O
2s
Be
F
Ne
N
3p
11
12
3
4
5
7
10
3s
Mg
6
8
9
S
Al
Na
Si
Cl
Ar
P
Noble gasses
4p
3d
Mn
Ge
Sc
Ti
Cr
Co
4s
K
V
Cu
Zn
Br
Ca
Ni
Se
Ga
Kr
Fe
As
5p
4d
5s
Sn
In
Rb
Sr
Xe
I
Te
Sb
6p
5d
6s
Cs
Ba
6d
7s
s block
4f
5f
4
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 Earths crust.
• The most direct method of producing hydrogen is
  the decomposition of water.
• The most active of the metals, those of Group 1A
  and the heavier members of Group 2A, displace
  H2(g) even from pure water.

5
Important Scientific Developments LinkedTo The
Element Hydrogen
6
Preparation Of Hydrogen

• Most often H2 is produced from water.
• Water gas reaction 1000oC
• C (s, coal or coke) H2O (g) CO (g) H2
  (g)
• Water gas shift reaction
• catalyst, 1000oC
• CO (g) H2O (g) CO2 (g) H2 (g)
• Reforming of methane major source of H2 now
• catalyst, 1000oC
• CH4 (g) H2O (g) CO (g) 3 H2 (g)
• Electrolysis of water
• electrolysis
• 2 H20 (l) 2 H2 (g) O2 (g)

7
The Electrolysis Of Water
8
Laboratory Preparation Of Hydrogen

• The most common reaction is that of a moderately
  active metal with a strong acid.
• Zn (s) 2 H (aq) ? Zn2 (aq) H2 (g)
• Mg (s) H2SO4 (aq) ? MgSO4 (aq) H2 (g)

9
Binary Compounds Of Hydrogen

• Hydrogen reacts with non-metals to form molecular
  compounds.
• H2 (g) Cl2 (g) ? 2 HCl (g)
• 3 H2 (g) N2 (g) ? 2 NH3 (g)
• Important molecular hydrides are those of
  carbon (organic chemistry).
• Hydrogen reacts with the most active metals to
  form ionic hydrides, in which hydrogen exists as
  the hydride ion, H-.
• 2 Na (s) H2 (g) ? 2 NaH
• Ca (s) H2 (g) ? CaH2 (s)
• Ionic hydrides react with water to liberate
  H2(g).
• CaH2 (s) 2 H2O (l) ? Ca(OH)2 (aq) 2 H2 (g)
• When hydrides are formed from transition
  elements, the products, called metallic hydrides,
  retain some metallic properties such as
  electrical conductivity.

10
Representing A Metal Hydride
11
Uses Of Hydrogen

• Manufacture of ammonia
• 3 H2 (g) N2 (g) ? 2 NH3 (g)
• Synthesis of methanol
• catalyst
• CO (g) 2 H2 (g) CH3OH (g)
• As reducing agent in metallurgy
• 850oC
• WO3 (s) 3 H2 (g) W (s) 3 H2O (g)
• Liquid hydrogen as a rocket fuel
• oxyhydrogen welding torch

12
The Alkali Metals
13
Properties And Trends in Group 1A

• The Group 1A metals exhibit regular trends for a
  number of properties.
• The atomic ionic radii increase from Li to Cs.
• The first ionization energy and electronegativity
  decrease from Li to Cs.
• From Li to Cs, the atoms become more metallic.
• The alkali metals are soft, conduct electricity
  well and have low melting points.
• Each element produces characteristic flame.
• They are quite reactive metals. Cations of 1
  charge are formed.

14
Diagonal Relationships The Special Case Of
Lithium

• In some of its properties, lithium and its
  compounds resemble magnesium and its compounds.
• 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.
• Lithium carbonate and lithium hydroxide decompose
  to form the oxide on heating, while the
  carbonates and hydroxides of other Group 1A
  metals are thermally stable.

15
Diagonal Relationships
16
Preparation Of Li, Na, K

• To convert an alkali metal ion into an alkali
  metal atom, the ion must take on an electron - a
  process of reduction.
• Na is obtained from electrolysis of molten NaCl.
• electrolysis
• 2 NaCl (l) 2 Na (l) Cl2 (g)
• Li is extracted mainly from spodumene,
  LiAl(SiO3)2. Some are from electrolysis of LiCl.
• K is obtained by reduction of KCl (l) with Na at
  850oC.
• 850oC
• KCl (l) Na (l) NaCl (l) K (g)

17
Typical Reactions Of The Alkali Metals
18
Uses Of Alkali Metals

• 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.
• Lithium is used in lightweight electrical
  batteries of the type found in clocks and
  watches, hearing aids, and heart pacemakers.
• Sodium is used as a reducing agent for other
  metals.
• MCl4 4 Na ? 4 NaCl M M Ti, Zr, Hf
• Potassium is used to produce KO2 which is used in
  life-support system.
• 4 KO2 (s) 2 CO2 (g) ? 2 K2CO3 (s) 3 O2 (g)

19
Important Compounds of Li, Na, K

• Li2CO3 is raw material for Li compounds.
• NaCl is raw material for Na compounds.
• Many Na compounds can be prepared from NaCl.
• KCl is raw material for K compounds.

20
Chemicals Produced From Sodium Chloride
21
Preparation Of Sodium Compounds From NaCl
22
The Solvay Process Chemical Process From An
Engineers Viewpoint
23
The Alkali Metals And Living Matter

• Hydrogen, oxygen, carbon, and nitrogen are the
  most abundant elements in the human body, in the
  order listed.
• 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.
• Lithium carbonate is used in medicine to level
  out the dangerous manic highs that occur in
  manic-depressive psychoses.

24
alkali metals
halogens
alkaline earth
main group elements
18
1
p block
2
13
16
17
15
14
H
He
transition metals d block
2p
Li
B
C
O
2s
Be
F
Ne
N
3p
11
12
3
4
5
7
10
3s
Mg
6
8
9
S
Al
Na
Si
Cl
Ar
P
Noble gasses
4p
3d
Mn
Ge
Sc
Ti
Cr
Co
4s
K
V
Cu
Zn
Br
Ca
Ni
Se
Ga
Kr
Fe
As
5p
4d
5s
Sn
In
Rb
Sr
Xe
I
Te
Sb
6p
5d
6s
Cs
Ba
6d
7s
s block
4f
5f
25
Properties Of The Group 2A Metals
26
Properties And Trends In Group 2A

• Group 2A shows the same general trends of
  increasing atomic and ionic sizes and decreasing
  ionization energies from top to bottom as does
  Group 1A.
• Except for Be, the metals have similar
  properties. They readily react to produce
  cations with 2 charge, and they are good
  reducing agents.
• The hydroxides and oxides are strong bases but
  they are not very soluble. The solubilities of
  the metal hydroxides of Group 2A in water
  increase from top to bottom.
• As the cation size increases, the interionic
  attractions that hold the crystalline solid
  together decrease in strength and the
  solubilities of the compounds in water increases.
• Be is more like Al than other alkali earth metals
  diagonal relationship.

27
Molecular Structure Of BeCl2
Cl Be Cl
Nonionic in molten state while all other alkaline
earth chlorides are almost entirely ionic
28
Preparation Of The Alkaline Earth Metals

• To obtain beryllium metal, beryl
  (3BeO.Al2O3.6SiO2) is first converted to BeF2.
  Then the BeF2 is reduced to beryllium, using
  magnesium as the reducing agent.
• BeF2 (g) Mg (l) 1000oC Be (s) MgF2 (s)
• Calcium is generally obtained by electrolysis of
  molten calcium chloride.
• Strontium and barium can also be obtained by
  electrolysis, but are usually obtained by the
  high-temperature reduction of their oxides, using
  aluminum as the reducing agent.
• Magnesium is obtained by the electrolysis of
  molten MgCl2, in a process called The Dow Process.

29
The Dow Process
30
Uses Of The Alkaline Earth Metals

• Alloys of beryllium with other metals have many
  applications such as springs, clips, and
  lightweight structural materials.
• Magnesium has a lower density than any other
  structural metal and is an important
  metallurgical reducing agent. Magnesium is also
  used in batteries and fireworks.
• Calcium is used to reduce the oxides or fluorides
  of less common metals to the free metals. Calcium
  is also used in the manufacture of batteries and
  in forming alloys with aluminum, silicon, and
  lead.

31
Reactions Of The Alkaline Earth Metals

• Reactions with water is more vigorous toward the
  bottom of the family.
• M (s) 2 H2O (I) ? M(OH)2 H2 (g) M Ca,
  Sr, Ba
• Mg does react with steam, but MgO is formed
  rather than Mg(OH)2.
• Mg (s) 2 H2O (g) ? MgO (s) H2 (g)
• All alkali earth metals react with dilute acids
  to displace hydrogen.
• M (s) 2 H (aq) ? M2 (aq) H2 (g)

32
Reactions Of The Alkaline Earth Metals

• The following reactions occur with Mg, Ca, Sr,
  Ba, NOT with Be.
• M (s) X2 ? MX2 (s) X2 F2, Cl2, Br2, I2
• 2 M (s) O2 (g) ? 2 MO (s)
• 3 M (s) N2 (g) ? M3N2 (s)

33
Important Compounds Of Mg And Ca

• Several magnesium compounds occur naturally,
  either in mineral form or in brines. These
  include the carbonate, chloride, hydroxide, and
  sulfate.
• Limestone is a naturally occurring form of
  calcium carbonate, containing some clay and other
  impurities.
• Calcium carbonate is the most widely used calcium
  compound.
• Gypsum has the formula CaSO42H2O. Another
  hydrate of calcium sulfate is plaster of paris
  which has the formula CaSO4 ½H2O and is obtained
  by heating gypsum.

34
Important Reactions of Ca Compounds

• ?
• Calcination CaCO3 (s) ? CaO (s) CO2 (g)
• lime or
• quicklime
• Hydration CaO (s) H2O (l) ? Ca(OH)2 (s)
• slaked lime
• Carbonation Ca(OH)2 (s) CO2 (g) ? CaCO3 (s)
  H2O (l)
• The three steps are combined and used to prepare
  chemically pure CaCO3(s) from limestone.

35
Some Important Mg Compounds
36
The 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 bones and teeth.
• Strontium is not essential to living matter, but
  it is of interest because of its chemical
  similarity to calcium.
• Barium also has no known function in organisms
  in fact the Ba2 ion is toxic.

37
Hard Water And Water Softening

• Hard water is groundwater that contains
  significant concentrations of ions from natural
  sources, principally Ca2, Mg2, and sometimes
  Fe2, along with associated anions.
• If the primary anion is the hydrogen carbonate
  ion, the hardness is said to be temporary
  hardness.
• If the primary anions are other than bicarbonate
  ion, then the hardness is called permanent
  hardness.
• 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.

38
Water Softening By Ion Exchange
39
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.
• 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 in other
  words, the soap softens the water first.

40
Cleaning Action Of A Soap
41
Summary

• The main sources of H2 are the electrolysis of
  water, the water-gas reactions, and reforming of
  hydrocarbons.
• Of the the elements, the Group 1A metals have the
  largest atomic radii and lowest ionization
  energies.
• The Group 2A metals have smaller atomic radii and
  greater ionization energies than the Group 1A
  metals.
• 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.