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Representative Elements - General Chemistry - Lecture Slides, Slides of Chemistry

Alagappa UniversityChemistry

You want to know about chemistry, start with general chemistry. This course introduces basic concepts and give you idea what is important in field of chemistry. Some key words of this lecture are: Representative Elements, Metalloids, Metals and Nonmetals, Ionization Energy, Periodic Table, Electron Affinity, Atomic Size and Group Anomalies, Metallurgy, Alkali Metals, Hydrogen

Typology: Slides

2012/2013

Uploaded on 09/26/2013

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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.
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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 4 f and 5 f orbitals.
  • Metalloids: separate metals from nonmetals, exhibit both metallic and nonmetallic properties.

Figure 19.1 The Periodic 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 P 4 molecules
  • O form O 2 molecule but S forms bigger aggregates, S 8.

Figure 19.2 The Atomic Radii of Some Atoms in Picometers

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) 2Sn(s) + CO2(g)

2PbO(s) + C(s) 2Pb(s) + CO2(g)

SnO(s) + H2(g) Sn(s) + H 2 O(g)

WO ( ) 3 3H ( ) 2 W( ) 3H O( )

heat

s  g l  2 g

heat    heat    heat  

Alkali Metals

  • The group 1A elements with their ns^1 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) + 2H 2 O(l)  2M+(aq) + 2OH-(aq) + H2(g)
  • Observed reducing abilities: Li>K>Na

Hydrogen

  • Hydrogen is a color less, odorless gas composed of H 2 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) + H 2 O(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, CaH 2 )

  • covalent hydrides: hydrogen + other

nonmetals (e.g, H 2 O, CH 4 , NH 3 )

  • metallic (interstitial) hydrides: transition

metal crystals treated with H 2 gas.

Alkaline Earth Metals

  • Group 2A elements are very reactive
  • Valence electron configuration ns^2
  • Lose 2 valence electrons to form noble gas configuration
  • Form ionic compounds containing M2+^ cations
  • Oxides are basic:

MO(s) + H 2 O(l)  M2+(aq) + 2OH-(aq)

  • Ca, Sr, and Ba reacts vigorously with water:

M(s) + 2H 2 O(l) M2+(aq) + 2OH-(aq) + H2(g)

  • Be form covalent bond because of small size and high electronegativity

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: large molecules that have many ionic sites.

Group 3A Elements

  • Valence electron configuration ns^2 np^1.
  • Increase metallic character in going down the

group.

  • B is a nonmetal and its compounds are covalent.
  • Boranes are hydride of B: diborane B 2 H 6
  • 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)

Group 4 Elements

  • Valence electron configuration ns^2 np^2
  • 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 sp^3

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)