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The Representative Elements. Ch 18 & 19. Representative Elements. Their chemical properties are determined by their valence (s and p) electrons. Properties are similar within a group, but first element in a group tends to act differently due to smaller size.

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representative elements
Representative Elements
  • Their chemical properties are determined by their valence (s and p) electrons.
  • Properties are similar within a group, but first element in a group tends to act differently due to smaller size.
  • Most abundant element is oxygen, followed by silicon.
  • Most abundant metals are aluminum and iron, which are found as ores.
group 1 1a alkali metals
Group 1 (1A) – Alkali Metals
  • Have Valence electron configuration ns1
  • Will lose 1 electron to form M+ Ions
  • React vigorously with water to form M+ and OH- ions and hydrogen gas.
  • React with oxygen to form oxides. Lithium will form a regular oxide (Li2O) while sodium will form a peroxide (Na2O2). Potassium, rubidium and cesium form superoxides (MO2)
hydrogen
Hydrogen
  • Can form covalent compounds with other nonmetals.
  • Will form salts, hydrides, with very active metals (group 1A and 2A).
  • Hydride ion, H-, is a strong reducing agent.
  • Covalent hydrides form when hydrogen bonds with other nonmetals.
  • Metallic hydrides occur when hydrogen atoms migrate into transition metal crystals.
group 2 2a alkaline earth metals
Group 2 (2A) – Alkaline Earth Metals
  • Have valence electron configuration ns2
  • Called Alkaline earth because of the basicity of their oxides.
  • React less vigorously with water than group 1.
  • Heavier alkaline earth metals form ionic nitrides and hydrides.
  • Hard water is caused by the presence of Ca+2 and Mg+2 ions.
group 13 3a
Group 13 (3A)
  • Have valence electron configuration ns2 np1
  • Show increasing metallic character goingdown the group.
  • Boron forms covalent compounds with hydrides called boranes. These compounds are highly electron deficient and very reactive.
  • Aluminum has some covalent characteristics as do indium and gallium.
  • Thallium is completely metallic in character.
group 14 4a
Group 14 (4A)
  • Have valence electron configuration ns2 np2
  • Show a change from nonmetallic to metallic properties going down the group.
  • All elements in this group form covalent bonds with nonmetals.
  • MX4 compounds (except carbon)react with Lewis bases to form two additional covalent bonds.
group 15 5a
Group 15 (5A)
  • Have varied chemical properties.
  • All members except nitrogen form molecules with 5 covalent bonds. (Nitrogen has no d sublevel)
  • Nitrogen and Phosphorous are nonmetals and form 3- anions in salts with active metals.
  • Antimony and bismuth are metallic. However their 5+ cations tend to be molecular rather than ionic.
nitrogen
Nitrogen
  • The strength of the triple bond in the N2 molecule is important both thermodynamically and kinetically as they decompose exothermically.
  • The nitrogen cycle is the process through which nitrogen is recycled through the environment.
  • Nitrogen forms a series of oxides in which it has an oxidation state ranging from 1 to 5.
  • Nitric acid is a strong acid which is important as a reducing agent.
  • Ammonia is the most important nitrogen hydride.
  • Has pyramidal molecules with polar bonds.
  • Hydrazine (N2H4) is a powerful reducing agent.
phosphorous
Phosphorous
  • Exists in three elemental forms: white, black and red.
  • Phosphine (PH3) has a structure analogous to that of ammonia but with bond angles closer to 90o.
  • Forms two oxides with oxidation states of 3+ and 5+.
group 16 6a
Group 16 (6A)
  • Shows the usual tendency of increasing metallic properties going down the group.
  • None behave as typical metals
  • Achieve noble gas configurations by adding two electrons to form 2- anions.
  • Form covalent bonds with other nonmetals.
  • Oxygen exists in two elemental forms: O2 and O3.
  • Sulfur has two elemental forms, both of which contain stacks of S8 rings.
  • Sulfur also forms two oxides: SO2 and SO.
  • Sulfur forms a variety of compounds in which it has a +6, +4, +2, 0 or -2 oxidation state.
group 17 7a halogens
Group 17 (7A) - Halogens
  • This group consist of all nonmetals.
  • Form hydrogen halides (HX) that behave as strong acids in water, except for hydrogen fluoride.
  • Oxyacids of the halogens become stronger as the number of oxygen atoms attached to the halogen increase.
  • Interhalogens are compounds of two different halogens
  • Halogen-carbon compounds are important industrially: examples are Teflon, PVC and the Freons.
group 18 8a noble gases
Group 18 (8A) – Noble Gases
  • Full valence shells ns2 np6
  • Generally unreactive.
  • Krypton, xenon and radon will form compounds with the highly electronegative elements fluorine and oxygen.