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Periodic Table Group 1a-8a Notes

Topics: Oxygen, Nitrogen, Hydrogen / Pages: 13 (3119 words) / Published: Jan 18th, 2013
Anderson Kuo
Period 1

CHAPTER 19 – The Representative Elements: Groups 1A through 4A

-19.1- A Survey of the Representative Elements

I. Elements

A. Representative Elements: Groups 1A through 8A ← Filling s and p orbitals ← First member of a group forms the strongest ( bonds; results in diatomic molecules

B. Transition Elements: center of the table ← Filling d orbitals

C. Lanthanides & Actinides: listed separately, on the bottom on the table ← Filling 4f and 5f orbitals

II. Metals/Nonmetals/Metalloids

A. Metals: ← Lose valence electrons to form cations ← Exhibiting valence electron configuration of the noble gas from the preceding period ← Metallic character increases going down a given group

B. Nonmetals: ← Gain electrons to form anions ← Exhibiting valence electron configuration of the noble gas in the same period.

C. Metalloids: ← separate metals from nonmetals

III. Abundance and Preparation

A. Oxygen – major element found in earth

B. 2nd most abundant element is silicon, found in earth’s crust, forms the basis of most sand, rocks and soil; most abundant metals are aluminum and iron, which are found in ores

C. Metallurgy: ← Process of obtaining a metal from its ore ← Always involves reduction ← Why metals? B/c metals are found in the form of cations. ← Carbon is often used in metallurgy; it is the primary reducing agent in the production of steel ← Carbon is the cheapest and most readily available industrial reducing agent for metallic ions

D. Liquefaction: ← The transformation of a gas to a liquid ← Based on the principle that a real gas cools when it expands. ← Process – After each expansion, part of the cooler gas is compressed, while the rest is used to carry away the heat of compression. The compressed gas is then allowed to expand again. Cycle is repeated. ← Main Idea – The remaining gas eventually becomes cold enough to form the liquid state. ← Examples> Elemental nitrogen & oxygen are obtained by this process, then separated by the distillation of liquid air.

-19.2- The Group 1A Elements

A. Alkali Metals ← ns1 valence-electron configurations ← Active metals; all react vigorously with water to release hydrogen gas

B. Lithium ← Lithium is the strongest of the alkali metals ← Results from the very large energy of hydration of the small Li+ ion. ← Relatively high charge density, the ion effectively attracts water molecules and releases a large quantity of energy ← Strongest reducing agent, but reacts more slowly with water than does sodium and potassium ← It has a higher melting point; does not become molten from the heat of reaction with water; smaller area of contact with water

C. Reactions with Oxygen ← Lithium is the only element that forms regular oxides of the general formula M2O in the presence of excess oxygen ← Sodium forms solid Na2O if the oxygen supply is limited, forms sodium peroxide

D. Superoxides ← A compound containing the O2- anion ← Potassium, Rubidium, and Cesium react with Oxygen to produce superoxides ← Superoxides release oxygen gas in reactions with water or carbon dioxide ← Useful in the self-contained breathing apparatuses used by firefighters ← Used in “airpacks” as emergency equipment in labs and production facilities in case toxic fumes are released

E. Alkali Metal Ions ← Important for proper functioning of nerves and mucles ← Examples: Na+ and K+ ions are present in all body cells and fluids ← The Li+ ions affect the levels of neurotransmitters, molecules that assist the transmission of messages along the nerve networks; used in treatment of manic-depressive patients

-19.3- Hydrogen

A. Properties ← Colorless, odorless gas composed of H2 molecules ← Low molar mass and nonpolarity = low boiling point and melting point ← Highly flammable; mixtures of air containing 18% to 60% hydrogen by volume are explosive ← Lab Demonstration – hydrogen gas and oxygen gases bubbles in soap water can be ignited and cause an explosion with a lighted candle on a long stick ← Behaves as a typical nonmetal, forming covalent compounds with other nonmetals and forming salts with active metals

B. Hydrides ✓ Binary compounds with hydrogen ✓ Ionic hydrides – formed when hydrogen combines with the most active metals (Group 1A and 2A) • Hydride ion = strong reducing agent – presence of two e- in the small 1s orbital produces large electron-electron repulsions and nucleus has only a 1+ charge • Placed in water ( violent reaction ✓ Covalent hydrides – formed when hydrogen combines with other nonmetals • Example: Water ▪ Polarity leads to a higher boiling point than expected of its molar mass, large heat vaporization, large heat capacity ▪ Higher density as a liquid than solid ▪ One of the few covalent hydrides that is nontoxic to organisms ✓ Metallic Hydrides – formed when transition metal crystals are treated with hydrogen gas • Hydrogen molecules dissociate at the metal’s surface, then the small hydrogen molecules migrate into the crystal structure to occupy holes (interstices). • Form solid solutions, rather than compounds • Hydrogen can be purified by placing it under slight pressure in a vessel containing a thin wall of palladium ( hydrogen diffuses into and through the metal wall and leaves the impurities behind

-19.4- The Group 2A Elements

A. Alkaline Earth Metals ← ns2 valence-electron configuration ← Very reactive, loses two valence electrons to nonmetals to form ionic compounds containing M2+ cations ← Only beryllium oxide also shows some acidic properties, dissolves in aqueous solutions containing hydroxide ions ← More active alkaline earth metals react with water, produces hydrogen gas

B. Importance ← Beryllium: its small size and relatively high electronegativity causes its bonds to be more covalent than a typical metal ← Calcium and magnesium ions are essential for human life • Calcium is found in the structural minerals constituting bones and teeth • Magnesium plays a vital role in metabolism and muscle functions; used to produce the bright light of photographic flash bulbs by reacting with oxygen; b/c of its low density and moderate strength, is a useful structural material • Hard water contains Ca2+ and Mg2+ ions ▪ Form precipitates with soap ▪ Usually removed by ion exchange resins that replace the Ca2+ and Mg2+ ions with Na+ (cation-exchange resin)

-19.5- The Group 3A Elements A. Boron Family ← ns2np1 valence electron configuration • shows the increase in metallic character in going down a group

B. Boron ← Boranes – covalent hydrides; compounds of boron • Electron-deficient = highly reactive • React with very exothermically with oxygen and were once evaluated as potential fuels for rockets in the U.S. space program • Example: BH3 ▪ Unstable compound ▪ The terminal B – H bonds are normal covalent bonds, each with one electron pair ▪ The bridging bonds are three-center bonds using a single pair of electrons to bond all three atoms • Example: B5H9 ▪ A square pyramidal ▪ Four three-center bonds around the base of the pyramid

C. Aluminum ← Most abundant metal on earth ← Properties: • High thermal and electrical conductivities, lustrous appearance • Bonds to nonmetals are significantly covalent; amphoteric nature (can behave as either an acid or base) ← Highly important structural material ← Has high strength –to-weight ratio; protects itself from corrosion by developing a touch, adherent oxide coating

D. Gallium ← Low melting point, extremely high boiling point = largest liquid range of an metal ← Useful for thermometers, especially to measure high temperatures ← Expands when it freezes

-19.6- The Group 4A Elements

A. Carbon Family ← ns2np2 valence-electron configuration ← contains two of the most important elements on earth: • carbon, the fundamental constituent of the molecules necessary for life, and silicon, which forms the basis of the geologic world ← lighter members are nonmetals; heavier metals are metals • all group members can form covalent bonds to nonmetals

B. Carbon ← Carbon compounds cannot react with Lewis bases to form two additional covalent bonds b/c of the small atomic size of carbon and because there are no d orbitals on carbon to accommodate the extra electrons ← Occurs in the earth’s crust mainly in two allotropic forms – graphite and diamond ← Carbon dioxide is a product of human and animal respiration and of the combustion of fossil fuels; produced by fermentation

C. Silicon ← Second most abundant element in the earth’s crust ← Approximately 85% of the earth’s crust is composed of silica and silicates ← Majorly used in semiconductors for electronic devices

D. Germanium ← Relatively rare element ← A semimetal used mainly in the manufacture of semiconductors for transistors and similar electronic devices

E. Tin ← A soft silvery metal ← Used for centuries in various alloys such as bronze, solder, and pewter ← Exists as three allotropes: white tin, gray tin, brittle tin ← When exposed to low temperatures, gradually changes to the powdery gray tin and crumbles away = tin disease ← Mainly used as a protective coating for steel

F. Lead ← Easily obtained from its ore ← Melts at a low temperature ← Used in the past by Egyptians and then later by the Romans to make eating utensils, glazes on potter, and plumbing systems ← Very toxic; lead poisoning

CHAPTER 20 – The Representative Elements: Groups 5A through 8A

-20.1- The Group 5A Elements

A. The Nitrogen Family ✓ ns2np3 valence shell electron configuration ✓ Group contains two nonmetals (nitrogen and phosphorus), two metalloids (arsenic and antimony), and a metal (bismuth)

B. Nitrogen ✓ Exists as a stable diatomic molecule ✓ The most abundant gas in the Earth’s atmosphere ✓ The triple nitrogen-nitrogen bonds in N2 molecules make nitrogen gas very stable and almost chemically inert ✓ Dispersion forces between N2 molecules are weak

C. Phosphorus ✓ Occurs in several allotropes; the white and red forms are the most common • White phosphorus ▪ Consists of individual tetrahedral P4 molecules ▪ Very reactive ▪ When exposed to air, it ignites spontaneously ▪ Low melting point ▪ Soluble in nonpolar solvents • Red phosphorus ▪ Consists of linear chains of the P4 molecules ▪ Obtained by heating white phosphorus in the absence of oxygen at 1 atm ▪ Less reactive ▪ Higher melting point ▪ Insoluble • Black phosphorus ▪ Obtained from either white or red phosphorus by heating at high pressures

D. Arsenic and Antimony ✓ Covalent network solid with high melting points

E. Bismuth ✓ Only metal in the group ✓ Heaviest element that contains stable isotopes

F. Important Trends in Chemical Behaviors ✓ Nitrogen can form a maximum of four covalent bonds ✓ Other elements in the 5A family can form more than four covalent bonds by utilizing one or more nd orbitals ✓ Nitrogen and phosphorus form simple anion with “-3” charge when reacted with very reactive metals ✓ Bismuth is primarily covalent in character, but forms ionic compounds with F2 or when reacted with nitric acid

-20.2- The Chemistry of Nitrogen

A. Nitrogen ✓ An inert molecule and will only react with other elements at very high temperatures ✓ The strength of the triple bond in the N2 molecule is important both thermodynamically and kinetically • Thermodynamically: great stability in the triple bond = most binary compounds containing nitrogen decompose exothermically to the elements, except ammonia (NH3) ▪ Thermodynamic stability of N2 is seen in the power of nitrogen based explosives (ex. Nitroglycerin, TNT – trinitrotoluene) ▪ An explosion = large volumes of gas produced in a fast, highly exothermic reaction ▪ Alfred Nobel discovered that if nitroglycerin is absorbed in porous silica, it can be handled safely • Kinetically: b/c most binary compounds containing nitrogen decompose exothermically, the value of K decreases significantly with a temperature increase ✓ Made available for biological processes by being fixed and converted into a form that can be absorbed by plants

B. Nitrogen Fixation ✓ The process of transforming N2 to other nitrogen-containing compounds (ex. Haber process) ✓ Results from the high-temperature combustion in automobiles ✓ Occurs naturally ✓ Nitrogen fixation includes: • Atmospheric fixation by lightening • Biological fixation by certain microbes – alone or in symbiotic relationship with plants • Industrial fixation

C. Atmospheric Fixation ✓ The enormous energy of lightening breaks N2 and O2 molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides ✓ The nitrogen oxides dissolve in rain and form nitrates ✓ Contributes to some 10% of total nitrogen fixed (traditionally)

D. Biological Fixation ✓ The ability to fix nitrogen is found only in certain bacteria ✓ The nitrogen-fixing bacteria readily allow the conversion of nitrogen to ammonia and other nitrogen-containing compounds useful to plants • Produce ammonia at soil temperature and 1 atm of pressure • Some live in a symbiotic relationship with plants of the legume family (ex. Alfalfa, soybeans)

E. Industrial Fixation ✓ Under great pressure and high temperatures, atmospheric nitrogen can combine with hydrogen to form ammonia ✓ Ammonia produced can be applied to the soil as fertilizer, important for the growth of plants ✓ Carried out by the Haber Process (at 250 atm and 400(C)

F. Decay ✓ Plants’ metabolism produces organic nitric compounds, which are microorganisms of decay ✓ Break down the molecules in dead organisms into ammonia

G. Nitrification ✓ Ammonia produced by decay is converted into nitrates (2 steps) 1. Bacteria of the genus Nitrosomonas oxidize ammonia into nitrites 2. Bacteria of the genus Nitrobacter oxidize the nitrites into nitrates

H. Denitrification ✓ The return of nitrogen from decomposed matter to the atmosphere by bacteria that change nitrates to nitrogen gas

I. Nitrogen Hydrides ✓ Most important hydride of nitrogen is ammonia – a toxic, colorless gas with a pungent odor ✓ Second nitrogen hydride of major importance is hydrazine (N2H4) • Colorless liquid with a pungent odor • A powerful reducing agent • Reacts vigorously with halogens • Used to produce porous plastics like Styrofoam products

J. Nitrogen Oxides ✓ Nitrogen forms a series of oxides in which it has an oxidation state from +1 to +5 ✓ Forms a series of oxides including N2O, NO, NO2, N2O3, and N2O5

K. Oxyacids of Nitrogen ✓ Nitric acid is an important industrial chemical used in the manufacture of many products • Is produced commercially by the oxidation of ammonia in the Ostwald process • Reacts with metal oxides, hydroxides, and carbonates ✓ Ostwald process 1. Ammonia is oxidized to nitric oxide 2. Nitric oxide reacts with oxygen to produce nitrogen dioxide 3. Absorption of nitrogen dioxide with water

-20.3- The Chemistry of Phosphorus

A. Phosphorus Oxides and Oxyacids ✓ Phosphorus reacts with oxygen to form oxides in which it has oxidation states of +5 and +3 ✓ Forms oxides including P4O6 and P4O10 ✓ P4O10 dissolves in water to form phosphoric acid, H3PO4 ✓ Phosphoric acid easily undergoes condensation reactions, where a molecule of water is eliminated in the joining of two molecules of acid ✓ P4O6 placed in water forms H3PO3 (a diprotic acid)

B. Phosphorus in Fertilizers ✓ Essential for plant growth ✓ Often present as insoluble minerals (inaccessible to plants) ✓ Soluble phosphate fertilizers are made by treating phosphate rock with sulfuric acid to make superphosphate of lime

C. Phosphorus Halides ✓ Phosphorus formas all possible halides of the general formulas PX3 and PX5, with the exception of PI5

-20.4- The Group 6A Elements

A. The Oxygen Family ✓ ns2np4 valence-electron configuration ✓ Most common chemical behavior – to achieve a noble gas configuration by adding two electrons to become a 2- anion in ionic compounds with metals ✓ Can form covalent bonds with other nonmetals

B. Selenium ✓ There is an inverse relationship between the incidence of cancer and the selenium levels in soil • Greater dietary intake of selenium furnishes protection from cancer ✓ Selenium is psychologically important ✓ Selenium deficiency leads to the occurrence of congestive heart failure ✓ A semiconductor

C. Polonium ✓ Has 27 isotopes and is highly toxic and radioactive

-20.5- The Chemistry of Oxygen ← Elemental forms are O2 and O3 • O2 and especially O3 are powerful oxidizing agents • O2 constitutes 21% of the volume of earth’s atmosphere ▪ Liquid O2 is a pale blue liquid • O3 (ozone) can be prepared by passing an electric discharge through pure oxygen gas ▪ The electrical energy disrupts the bonds in some O2 molecules to give oxygen atoms, which react with other O2 molecules to form O3 ▪ A pale blue, highly toxic gas ▪ Ozonolysis – ozone as a replacement for chlorine in municipal water purification ▪ Exists in the upper atmosphere of the earth ▪ Absorbs ultraviolet light and acts as a screen to prevent radiation from penetrating the earth’s surface

-20.6- The Chemistry of Sulfur ← Sulfur is found in nature both in large deposits of the free element and in widely distributed ores ← 60% of sulfur produced comes from underground deposits (Texas and Louisiana) ← Recovered by the Frasch process 1. Superheated water is pumped into the deposit to melt the sulfur 2. Molten sulfur is forced to the surface by air pressure ← Elemental sulfur only exists as S2 molecules only in the gas phase at high temperatures ← Because sulfur atoms form much stronger ( bonds than ( bonds, S2 is less stable at 25(C ← Most stable form of sulfur at 25(C and 1 atm is rhombic sulfur ← The elemental forms, rhombic and monoclinic sulfur, both contain S8 molecules

A. Sulfur Oxides and Oxyacids ✓ Most important oxides are SO2 (which forms H2SO3 in water) and SO3 (which forms H2SO4 in water) ✓ SO3 is a corrosive gas with a choking odor that forms white fumes of sulfuric acid when it reacts with moisture in the air

B. Other Compounds of Sulfur ✓ Sulfur reacts with both metals and nonmetals to form a wide variety of compounds in which it has a +6, +4, +2, 0, or -2 oxidation state

-20.7- The Group 7A Elements

A. The Halogens ✓ ns2np5 valence-election configuration ✓ Because of their high relativities, the halogens are not found as the free elements of nature; found as halide ions (X-) in various minerals and in seawater ✓ Have very high electronegativity values ✓ Tend to form polar covalent bonds with other nonmetals and ionic bonds with metals in their lower oxidation states

B. Hydrogen Halides ✓ Gaseous hydrogen and gaseous halogens produce hydrogen halides ✓ Can be prepared by treating halide salts with acid ✓ When dissolved in water, the hydrogen halides behave as acids, and all except hydrogen fluoride (a weak acid) are completely dissociated ✓ Hydrogen fluoride is considered a weak acid; although the enthalpy of hydration favors dissociation of HF, the entropy of hydration strongly opposes it ✓ HCl is the most important of the hydrohalic acids (the aqueous solutions of the hydrogen halides).

C. Oxyacids and Oxyanions ✓ All the halogens except fluorine combine with various numbers of oxygen atoms to form a series of oxyacids ✓ Disproportionation reaction – where a given element is both oxidized and reduced

D. Other Halogen Compounds ✓ The halogens react readily with most nonmetals to form a variety of compounds ✓ Halogens react with each other to form interhalogen compounds • General formula: ABn, where n is typically 1, 3, 5, or 7 and A is the larger of the two halogens • Interhalogens are volatile, highly reactive compounds that acts as strong oxidizing agents • React readily with water

-20.8- The Group 8A Elements

A. The Noble Gases ✓ Electron configuration of 2s2 for helium and ns2np6 for the others ✓ All the group 8A elements are monatomic gases and are generally very unreactive ✓ The heavier elements form compounds with electronegative elements such as fluorine and oxygen ✓ Helium was identified by its characteristic emission spectrum; formed from α-particle decay of radioactive elements; important substance that is used as a coolant ✓ Neon is employed in luminescent lighting ✓ Argon is used to provide the noncorrosive atmosphere in incandescent light bulbs ✓ Only krypton and xenon form chemical compounds

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