Chapter 20 The Representative Elements. Section 20.1 A Survey of the Representative Elements Return...

Chapter 20

The Representative Elements

Section 20.1

A Survey of the Representative Elements

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The Atomic Radii of Some Representative Elements (in Picometers)

Section 20.2

Atomic MassesThe Group 1A Elements

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Reaction of Group 1A Metals

• Reactions with water:

2Li(s) + 2H2O → 2LiOH(aq) + H2

2Na(s) + 2H2O → 2NaOH(aq) + H2

2K(s) + 2H2O → 2KOH(aq) + H2

2Rb(s) + 2H2O → 2RbOH(aq) + H2

2Cs(s) 2H2O → 2CsOH(aq) + H2

2X(s) 2H2O → 2XOH(aq) + H2

Section 20.2


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• In the presence of excess oxygen:

4Li + O2 → 2Li2O

2Na + O2 → Na2O2

K + O2 → KO2

Rb + O2 → RbO2

Cs + O2 → CsO2

• In the presence of a halogen:

2Na + Cl2 → 2NaCl

Section 20.2


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Reactions of Group 1A Oxides

In water…• oxides form hydroxides

Li2O + H2O → 2LiOH

• peroxides form hydroxides and hydrogen peroxide

Na2O2 + 2H2O → 2NaOH + H2O2

• superoxides form hydroxides and hydrogen peroxide and oxygen

2KO2 + 2H2O → 2KOH + 2H2O2 + O2


Section 20.2


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Reactions of Group 1A Oxides continued…

• In dilute acid, instead of a base forming, an acid-base reaction occurs and forms a salt and the other products from reaction with water.

Li2O + HCl → LiCl + H2O

Na2O2 + HCl → NaCl + H2O2

KO2 + HCl → KCl + H2O2 + O2


Section 20.3

The Mole The Chemistry of Hydrogen

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Hydrides

• Binary compounds containing hydrogen: Ionic hydrides:

hydrogen + the most active metals (group I and group II)

(eg; LiH, CaH2)

Covalent hydrides:hydrogen + other nonmetals

(eg; H2O, CH4, NH3)

Metallic (interstitial) hydrides:transition metal crystals treated with H2 gas

Section 20.3


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Exercise

Predict the products formed by the following reactants:

LiH(s) + H2O(l) → H2(g) + LiOH(aq)

Ionic hydrides react with water to produce hydrogen gas and a hydroxide.

Section 20.3


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• Reactions with water:

Be has no rxn with water

Mg(s) + H2O(l) → Mg(OH)2(s) + H2

Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2

Sr(s) + 2H2O(l) → Sr(OH)2(aq) + H2

More reactive with water as you go down the group

X(s) + 2H2O → X(OH)2(aq) + H2

Section 20.4

The Group 2A Elements

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Reactions of Group 2A Metals


Section 20.5


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• Group 3A elements generally show the increase in metallic character in going down the group that is characteristic of the representative elements.

• B, Al, Ga, In, Tl

• Notice that Boron is a nonmetal!

Section 20.5


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Some Important Reactions

Section 20.5


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Complex ion formation of Al

• Al(H2O)63+ ↔ Al(OH)(H2O)5

2+ + H+

• Salt that produces an acidic solution

• Lewis acid base reaction


What species is acting as the Lewis acid? Lewis base?

Al OH-

Section 20.6


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• Contains two of the most important elements on earth: carbon and silicon.

• Can form four covalent bonds to nonmetals. CH4, SiF4, GeBr4

Section 20.8

The Chemistry of Nitrogen

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• Exhibits varied chemical properties. • N, P, As, Sb, Bi • Compounds of N

– NH3 NF3 only 3 bonds total

• Compounds of P – PH3, PF3, but also PF6 How???

Section 20.8


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Nitrogen Fixation

• The process of transforming N2 to other nitrogen–containing compounds.

• The Haber Process:

N2(g) + 3H2(g) → 2NH3(g)

∆Ho = -92 kJ

Section 20.8


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Nitrogen Oxides

• Nitrogen in its oxides has oxidation states from +1 to +5. In other compounds, nitrogen could have oxidation

states of -1 to -3.

Compound Oxidation State of N

N 2O +1

NO +2

N 2O3 +3

NO 2 +4

HNO 3 +5

Section 20.8


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Nitrogen Oxyacids

• Nitric acid, HNO3 (strong acid)

• Nitrous acid, HNO2 (weak acid)

3 2 2 24HNO ( ) 4NO ( ) + 2H O( ) + O ( ) hvl g l g

+2 2HNO ( ) H ( ) + NO ( )aq aq aq

Section 20.8


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The Ostwald Process

Section 20.9

The Chemistry of Phosphorus

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Phosphorus Oxyacids

• P4O10 + H2O → H3PO4 (phosphoric acid)

• P4O6 + H2O → H3PO3 (phosphorous acid)

• Hypophosphorous acid, H3PO2

Section 20.12

The Chemistry of Sulfur

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Sulfur Oxide Reactions

2SO2(g) + O2(g) → 2SO3(g)

SO2(g) + H2O(l) → H2SO3(aq) (sulfurous acid)

SO3(g) + H2O(l) → H2SO4(aq) (sulfuric acid)

Section 20.13


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Preparation of Hydrogen Halides

H2(g) + X2(g) 2HX(g)

• When dissolved in water, the hydrogen halides behave as acids, and all except hydrogen fluoride are completely dissociated (strong acids)

Section 20.13


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Halogen Oxyacids and Oxyanions

• All halogens except fluorine combine with various numbers of oxygen atoms to form a series of oxyacids

• Notice the varying oxidation states of the halogen.

Section 20.13


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Halogen Oxyacids and Oxyanions

• The strengths of these acids vary in direct proportion to the number of oxygen atoms attached to the halogen, with the acid strength increasing as more oxygens are added.


Section 20.14


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Noble Gases

• He and Ne form no compounds.• Kr and Xe have been observed to form

chemical compounds:

Xe(g) + 2F2(g) → XeF4(s) [6 atm, 400oC]

XeF6(s) + 3H2O(l) → XeO3(aq) + 6HF(aq)

Section 20.14


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Of course there are more reaction types to consider

• Refer to Packet from Winter Break for more reaction types

• (Ch 9, 10, 13 Chemical Equations Handouts)


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