19.2-.3 Luc LaLonde

19.2 Group 1A Elements (Excluding Hydrogen)

• Very active metals due to ns1 valence electron configuration.

• Alkali metals

Sources

• Lepidolite contains several pure alkali metals such as lithium, rubidium and, cesium

Reaction With Water

• React vigorously with water to release Hydrogen gas• 2M(s) + 2H2O(l) 2M+(aq) + 2OH-(aq) + H2(g)• Would expect lithium to be weakest alkali metal as a

reducing agent in water but this is not the case.• Because of its high charge density, the Li+ ion very

effectively attracts the water molecule. A lot of energy is released in this process, favoring the formation of Li+ and making Lithium a strong reducing agent in aqueous solutions

Notice Ionization energy and Radius

The Need for Speed

• Lithium strongest reducing agent but not fastest reacting.

• (Rate controlled by kinetic factors)• Lithium reacts slower because it has a higher

melting point than other elements, such as sodium and potassium, which means that it doesn’t become molten from the heat of reaction. Sodium and Potassium become molten which increases surface area (A factor that increases the rate of reaction)

Types of Compounds Formed by Alkali Metals With Oxygen

(3-All Ionic)

1. Oxides

• M2O• Lithium does when excess oxygen is present• 4Li(s) + O2(g) 2Li2O(s)

2. Peroxides

• M2O2

• O22- anion

• 2Na(s) + O2(g) Na2O2(s)

• Reaction with WaterNa2O2(s)+2H2O(l)2Na+(aq)+H2O2(aq)+2OH-(aq)

3. Superoxides

• Potassium, rubidium, and cesium react with oxygen to produce superoxides.

• MO2

• O2- anion

• K(s) + O2(g) KO2(s)• Release oxygen gas in reactions with water or carbon

dioxide. Useful for self contained breathing packs for fire fighters.

2MO2(s)+2H2O(l)2M+(aq)+2OH-(aq)+O2(g)+H2O2(aq)4MO2(s) + 2CO2(g) 2M2CO3(s) + 3O2(g)

In Summary

Alkali Metals in Biology

• Important for functioning of body• Sodium and potassium ions in all body cells• Blood plasma has [Na+]=0.15M [K+]=0.005M

– Fluids inside cells are opposite [Na+]=0.005M [K+]=0.15M– Lithium Carbonate used for manic-depressive patients– Li+ affects neurotransmitters

Practice Problem 1

• Predict the products formed by the following reactants

• 1. Li3N(s) + H2O(l)

• 2. KO2(s) + H2O(l)

Answers

1.Solid Li3N contains the N3- anion, which has a strong attraction for three H+ ions to form NH3.

Li3N(s) + 3H2O(l) NH3(g) + 3Li+(aq) + 3OH-(aq)

2. 2KO2(s)+2H2O(l)2K+(aq)+2OH-(aq)+O2(g)+H2O2(aq)

19.3 Hydrogen

• Low boiling point• Low melting point• Flamable-mixtures of air containing from 18%

to 60% hydrogen by volume are explosive• Source- reaction of methane and water at high

temperatures and pressuresCH4 + H2O(g) =================> CO(g) + 3H2(g)

(Heat, Pressure, Catalyst)

More Sources

• By product of gasoline production, in which hydrocarbons with high molar masses are broken down (cracked) to produce smaller molecules more suitable for use as motor fuel.

• Electrolysis of water- not efficient due to high costs of electricity for this process.

Uses

• Hydrogenating unsaturated vegetable oils through Haber Process

Types of Hydrides, Binary Compounds Containing Hydrogen

(3 Classes)

Ionic Hydrides

• H- anion (hydride ion)• Cation from Group 1A or 2A• Ex: LiH and CaH2

• Hydride ions are strong reducing agents due to 1s electron repulsions

• Violently react with waterLiH(s) + H2O(l) H2(g) + Li+(aq) + OH-(aq)

Covalent Hydrides

• Hydrogen and other non-metals• Ex: HCl, NH3, H2O

• Water is most important covalent hydrides due to all the amazing things that water does

• Water is one of the few covalent hydrides that is non-toxic to humans

Metallic (or Interstitial) Hydrides

• Formed when transition metal crystals are treated with hydrogen gas. The hydrogen molecules dissociate at the metals surface, and the small hydrogen atoms migrate into the crystal structure to occupy holes.

• Palladium can absorb 900 times its volume of hydrogen gas.

• Non-stoich formulas such as LaH2.76

• Much of absorbed hydrogen is released upon heating.• Could be used in engines as means of storage of

Hydrogen gas for combustion in car engines.