Transcript Chapter 19 The Representative Elements: Group 1A through 4A

Chapter 19
The Representative Elements:
Group 1A through 4A
Reviewing the Periodic Table Regions:
• Representative elements: Groups 1A - 8A - filling s and
p orbitals (s and p valence electrons).
• Transition elements: Center of the table - filling d
orbitals.
• Lanthanides, Actinides: listed separately, on the
bottom of the table - filling 4f and 5f orbitals.
• Metalloids: separate metals from nonmetals, exhibit
both metallic and nonmetallic properties.
Figure 19.1 The Periodic Table
Metals and Nonmetals
• Metals:
–
–
–
–
Lose one or more valence electrons
Form cations (positive ions)
Low ionization energy
Found on the left side of the periodic table
• Nonmetals:
–
–
–
–
–
Gain one or more electrons
Form anions (negative ions)
Large ionization energy
Most negative electron affinity
Found on the right side of the table
Atomic Size and Group Anomalies
• Atomic size increases down a group.
• Large increase in atomic radius in going from first to
second member.
• First element shows properties that are quite different
from the others.
• Hydrogen is a nonmetal but lithium is a very active
metal.
• BeO is amphoteric but other group 2A oxides are basic.
• Usually C forms C-C bonds but Si forms Si-O bonds
• N forms :NN: but P forms tetrahedral P4 molecules
• O form O2 molecule but S forms bigger aggregates, S8.
Figure 19.2 The Atomic Radii of Some Atoms in Picometers
Figure 19.3 The Structure of Quartz
Metallurgy
. . . the process of obtaining a metal from its ore.
This always involves reduction of the ions to the
elemental metal (oxidation state = 0).
Reducing agents are used to produce the metals
from their ores.
2SnO(s) + C(s) heat
 2Sn(s) + CO2(g)
2PbO(s) + C(s) heat
 2Pb(s) + CO2(g)
SnO(s) + H2(g) heat
 Sn(s) + H2O(g)
WO3 (s)  3H2 ( g)
heat
W(l )  3H2O( g)
Alkali Metals
• The group 1A elements with their ns1 valence electron
configurations are very active metals. They lose their
valence electrons very readily. They have low ionization
energies and react with nonmetals to form ionic solids.
2Na(s) + Cl2(g)  2NaCl(s)
• The expected trend in reducing ability,
Cs>Rb>K>Na>Li
• Alkali metals all react vigorously with water to release
hydrogen gas.
2M(s) + 2H2O(l)  2M+(aq) + 2OH-(aq) + H2(g)
• Observed reducing abilities: Li>K>Na
Group 1A Oxides
In the presence of ample oxygen,
4Li + O2  2Li2O (regular oxide)
2Na + O2  Na2O2 (peroxide)
K + O2  KO2 (superoxide)
Rb + O2  RbO2 (superoxide)
Cs + O2  CsO2 (superoxide)
Hydrogen
• Hydrogen is a color less, odorless gas composed of H2
molecules.
• Because of its low molar mass and nonpolarity,
hydrogen has a low boiling point (-253oC) and melting
point (-260oC).
• Industrial source: methane reacts with water at high
temp.(800-1000oC) and high pressure (10-50 atm) in
presence of nickel catalyst
CH4(g) + H2O(g)  CO(g) + 3H2(g)
• Hydrogen can be produced by electrolysis of water
which is not economically feasible because of the high
cost of electricity.
• The major industrial use of hydrogen is in the
production of ammonia.
Hydrides
. . . are binary compounds containing
hydrogen.
• ionic hydrides: hydrogen + the most
active metals (e.g, LiH, CaH2)
• covalent hydrides: hydrogen + other
nonmetals (e.g, H2O, CH4, NH3)
• metallic (interstitial) hydrides: transition
metal crystals treated with H2 gas.
Figure 19.5 The Structure of Ice, Showing the Hydrogen Bonding
Alkaline Earth Metals
• Group 2A elements are very reactive
• Valence electron configuration ns2
• Lose 2 valence electrons to form noble gas
configuration
• Form ionic compounds containing M2+ cations
• Oxides are basic:
MO(s) + H2O(l)  M2+(aq) + 2OH-(aq)
• Ca, Sr, and Ba reacts vigorously with water:
M(s) + 2H2O(l) M2+(aq) + 2OH-(aq) + H2(g)
• Be form covalent bond because of small size and high
electronegativity
The Structure of Solid BeH2
Figure 19.6 Preparation for the Group 2A Elements
Ion Exchange
• Ca2+ and Mg2+ ions cause the hardness of water.
These ions of hard water interfere with the action
of detergents and form precipitate with soap.
Those ions are removed by ion exchange with ion
exchange resins.
• Ca2+ and Mg2+ are often removed during ion
exchange, releasing Na+ into solution.
• Ion exchange resin:
many ionic sites.
large molecules that have
Group 3A Elements
• Valence electron configuration ns2np1.
• Increase metallic character in going down the
group.
• B is a nonmetal and its compounds are covalent.
• Boranes are hydride of B: diborane B2H6
• Al is the most abundant metal on earth.
• Al forms covalent bond with nonmetals
• Gallium has unusually low melting point at
29.8oC (Al:660oC)
Figure 19.8 The Structure of B2H6
Group 4 Elements
• Valence electron configuration ns2np2
• C and Si are the two most important elements
on earth
• Increase metallic character in going down the
group
• C is a nonmetal, Si & Ge are semimetals, Sn
and Pb are metals
• All elements form four covalent bond to
nonmetals
Group 4 Elements
continued…
• Form tetrahedral molecules because of sp3
hybridization
• Carbon occurs as graphite and diamond
• Si forms silica and silicates are the most
abundant of the earth crust
• Ge used in the manufacture of semiconductors
• Sn used in various alloys such as bronze (20%
Sn and 8% Cu)
Inert Pair Effect
• The tendency for the heavier elements of
Groups 3A and 4A to exhibit lower
oxidation states as well as their expected
oxidation states.
• Group 3A +1 and +3 oxidation states
• Group 4A +2 and +4 oxidation states