CHE2C Main Groups

Group 1A Elements

• alkali metals

• all elements have #s^1 VE config EXCEPT for hydrogen (non-metal)

• react vigorously with H2O to release hydrogen gas

  • this becomes more violent as you go down the group

  • Fr > Cs > Rb > K > Na > Li > H

    • reason is for increasing metallic character

• essential for the proper functioning of nerves and muscles

  • ex) Na and K (proton bump)

Method of Preparation (Group 1A Elements)

• lithium

  • electrolysis of molten LiCl

• sodium

  • electrolysis of molten NaCl

• potassium

  • electrolysis of molten KCl

• rubidium

  • reduction of RbOH with Mg and H2

• Cesium

  • reduction of CsOH with Mg and H2

Selected Reactions (Group 1A Elements)

• halogenation

• oxidation

  • hydrogen peroxide is very famous oxidizing agent

    • over the counter medicine, mouth wash, antiseptic

• reaction with water (violent)

Hydrogen

• in the alkali metal (but nonmetal)

• physical

  • colorless, odorless gas

  • low molar mass and non-polar

  • highly flammable

• sources

  • industrial

    • reaction of methane with water at high temp and pressure with metallic catalyst

  • electrolysis of water

    • produces pure hydrogen

  • by-product of gasoline production

• uses

  • industrial

    • production of ammonia by HABER process

  • hydrogenation of unsaturated vegetable oils

Hydrogen Hydrides

• since hydrogen behaves like non-metal, it forms covalent compounds with other nonmetals and salts with active metals

• hydrides

  • binary compounds containing hydrogen

• ionic hydride

  • formed when hydrogen combines with most active metals (Group 1A and 2A)

  • acts as strong reducing agent (strong base)

• covalent hydride

  • formed when hydrogen combines with other nonmetals

  • most important covalent hydride is water (H2O)

• metallic (interstitial) hydrides

  • formed when transition metal crystals are treated with hydrogen gas

  • appear to be solid solutions

  • compositions of nonstoichiometric hydrides vary with the length of exposure of the metal to hydrogen gas

  • lose much of the absorbed hydrogen as gas when heated

Unusual Properties of Water

• high boiling point

• polarity of molecules attribute to water’s unusual properties

• large heat of vaporization and heat capacity

• higher density in liquid form than solid form

• excellent solvent for ionic and polar substances

Group 2A Elements

• alkaline earth metals

• all have the same VE configuration

• very reactive

• oxides are very basic EXCEPT BeO (beryllium oxide) which shows acidic properties

• the more active alkali metals react with water (which produces H2 gas)

• at 25*C, Ca, Sr, Ba react vigorously while Be and Mg show no reaction

  • Mg reacts with boiling water

Calcium

• alkaline earth metals

• found in structural minerals that compose bones and teeth

Magnesium

• alkaline earth metal

• essential in metabolism and muscle function

• useful structural material because of its low density and moderate strength

Method of Preparation (Group 2A elements)

• all are electrolysis of halide

  • X + Cl (n)

Group 2A Ion Exchange

• hard water

  • natural water that contains Ca2+ and Mg2+ interfere with action of detergents and form precipitates with soap

• ion exchange

  • process that removes Ca2+ and Mg2+ in individual homes (water softener)

Group 2A Selected Reactions

• halogenation

• oxidation

• reaction with water

Group 3A Elements

• no specific name

• all same VE configuration

Boron

• group 3A element

• technically metalloid, generally act as typical nonmetal

  • so it forms covalent compounds

• boranes

  • covalent hydride compounds

  • very reactive/explosive

  • react exothermically with oxygen

Aluminum

• group 3A element

• most abundant metal on earth

• contains metallic properties

  • conducts heat and electricity

  • lustrous appearance

• forms covalent bonds with nonmetals

Gallium

• group 3A element

• low melting point and high boiling point

  • largest liquid range of any metal

• used in thermometers

• expands when freezes

• similar to that of aluminum

Indium

• group 3A element

• has chemistry similar to aluminum and gallium

• compounds containing 1+ and 3+ ions

Thallium

• group 3A element

• chemistry is completely metallic

Group 3A Selected Reactions

• halogenation

• oxidation

Group 4A elements

• no specific name

• all have same VE configuration

• form four covalent bonds to nonmetals

• carbon forms pi bonds

Carbon

• group 4A element

• fundamental constituent of molecules that are necessary for life

• occurs in allotropic forms of graphite, diamond, and fullereness

Silicon

• group 4A element

• forms the basis for the geological world

• semimetal that is found widely distributed in silica and silicates

Germanium

• group 4 A element

• rare element and semimetal

  • used in manufacturing of semiconductors for transistors and similar electronic devices

Tin

• group 4A element

• soft, silvery metal that can be rolled into thin sheets

• used in alloys and as a protective coating for steel

• tin disease

Lead

• group 4A element

• ore

• melts at low temperature

• has been in use since 3000 BC

• used in batteries in automobiles

• toxic in nature

Group 4A Selected Reactions

• halogenation

• oxidation

Group 5A Elements

• no specific name

• all have same VE config

• exhibit varied chemical properties

  • nitrogen and phosphorus are non-metals, gain three electrons to form 3- anions in salts with active metals

  • bismuth and antimony exhibit metallic properties

• capable of forming molecules with 5 covalent bonds EXCEPT nitrogen

  • VSEPR model - trigonal bipyramidal with central atom is dsp3 hybridized

• the ability to form pi bonds decreases after nitrogen

Group 5A Method of preparation

• nitrogen = liquefaction of air

Nitrogen

• group 5A element

• percentage of nitrogen in air is 79%-80%

• all elemental nitrogen exists as N2 molecules with strong triple bonds

  • unreactive

  • can coexist with almost all other elements without undergoing reaction

  • useful medium for experiments conducted using inert atmosphere box

• nitrogen based explosives

  • nitroglycerin

    • 4 moles of liquid nitroglycerin produce 29 moles of gaseous products

  • trinitrotoluene (TNT)

    • 2 moles of solid TNT produce 20 moles of gaseous products and energy

• nitrogen fixation

  • process of transforming N2 to other nitrogen-containing compounds (haber process —> ammonia)

  • in nature, bacteria converts nitrogen to ammonia and urea (fertilizer)

Nitrogen Hydride, Oxides, and Oxyacids

• hydride

  • ammonia

    • toxic and colorless gas

  • hydrazine

    • powerful reducing agent

    • rocket propellant

• oxide

  • dinitrogen monoxide

    • laughing gas

    • mild anesthetic

    • produced by microorganisms in soil

    • controls earth’s atmosphere by absorbing infrared radiation

  • nitrogen monoxide

• oxyacids

  • nitric acid

    • makes explosives

    • produced by ostwald process

    • common laboratory reagent and strong oxidizing agent

    • nitrating agent

Phosphorus

• group 5A elemnt

• phosphides

  • Na3P and Ca3P

  • phosphide salts react vigorously with water to produce phosphine

  • colorless, toxic gas that is analogous to ammonia

• phosphorus oxyacids

  • phosphoric acid

    • weak acid

    • poor oxidizing agent

Group 6A Elements

• chalcogens

• none of these elements behave as typical metals (nonmetals)

• have common chemical behavior where they react with metal to attain noble gas configuration

• form covalent bonds with other nonmetals

Selenium

• group 6A element

• show inverse relationship between the incidence of cancer and the selenium levels in soil

  • high selenium = decreased cancer rate

polonium

• group 6A element

• highly toxic and radioactive

  • polonium - 210 is natural containment of tobacco

  • responsibly for cancer in smokers

Oxygen

• group 6A element

• present in atmosphere as gas / ozone, soil / rocks, water, humans

• reacts with carbon containing molecules (combustion) to provide energy

• comprises 21% of volume of earth’s atmosphere

• paramagnetic in nature

• ozone (O3)

  • prepared by passing an electrical discharge through pure oxygen gas

  • less stable than oxygen, highly toxic

  • exists naturally in upper atmosphere

  • powerful oxidizing agent

    • used to kill bacteria in pools / aquariums

    • used in municipal water treatment and washing produce after it comes out of fields

Sulfur

• group 6A element

• found in nature as large deposits of free element, ores like galena and gypsum

• recovered using frasch process

  • superheated water is pumped into a deposit to melt sulfur

  • sulfur is forced to the surface by air pressure

• aggregates of sulfur and their stability

  • exists as S2 molecules in gas phase at high temperature

  • S2 less stable at 25*C than its larger aggregates like S6 or S8

  • most stable form of sulfur is S8

Sulfur Oxides and Oxyacids

• oxides

  • sulfur monoxide

    • highly unstable

    • weak pi bonds

  • sulfur dioxide

    • produce when sulfur is burned in air

    • colorless gas with pungent odor

  • sulfur trioxide

  • all good efficient antibacterial agent

• oxyacid

  • sulfurous acid

  • sulfuric acid

  • good lead storage batteries

  • dehydrating agent because of the high affinity for water

Group 7A Elements

• halogens

• all have same VE config

• nonmetals whose properties vary smoothly while going down the group

  • exceptions

    • low electron affinity of fluorine

    • small bond energy of F2 elements

• have high reactivities

  • cannot be found as free elements

• have high electronegativity values

  • form polar covalent bonds with nonmetals

  • form ionic bonds with metals in their low oxidation states

Group 7A Selected Physical Properties

• fluroine

  • EN: 4.0, radius: 136

• chlorine

  • EN: 3.0, radius: 181

• bromine

  • EN: 2.8, radius: 195

• iodine

  • EN: 2.5, radius: 216

• astatine

  • EN: 2.2, radius: X

Method of Preparation Group 7A

• chlorine = electrolysis of aqueous NaCl

Hydrogen Halides, Acids, Oxyacids and Oxyanions with Group 7A

• halides

  • reaction occurs with explosive vigor when fluorine and hydrogen mix

  • hydrogen and chlorine have little reaction in dark with while react rapidly in presence of UV light

  • bromine and iodine react with hydrogen at slow rate

  • behave as acids

    • exception: hydrogen fluoride

    • acid strength trend

      • H-I > H-Br > H-Cl > H-F

      • strongest —> weakest

• hydrohalic acids

  • hydrochloric acid

    • used for cleaning steel prior to galvanization

  • hydrofluoric acid

    • used to etch glass

• oxyacids and oxyanions

  • strengths of acids vary in direct proportion to the number of oxygen atoms attached to halogen

    • acid strength increases as more oxygen atoms are added

  • perchloric acid

    • powerful oxidizing agent

  • hypochlorous acid

    • acid and its salts are strong oxidizing agents

    • used as disinfectants and household bleaches

  • chlorate salts

    • strong oxidizing agent

    • used as weed killers and in fireworks / explosives

Group 8A Elements

• noble gases

• highly unreactive

• all have same VE config EXCEPT He (2S2)

Helium

• group 8A element

• found in natural gas deposits

• does not form compounds

• used as coolant, pressurizing gas for rocket fuels, and diluent in gasses which are used in deep-sea diving and spaceship atmospheres

Neon

• group 8A element

• does not form compounds

• used in neon signs

Argon

• group 8A element

• forms chemical bonds under certain circumstances

• provides a noncorrosive atmosphere in incandescent light bulbs

Krypton and Xenon

• form many stable chemical compounds