Chapter 19 The Representative Elements: Groups 1A Through 4A

19.1 Survey of the Representative Elements Elements in group 1A through 8A are called representative elements because they display a wide range of physical and chemical properties. Elements in group 1A through 8A are called representative elements because they display a wide range of physical and chemical properties. Representative elements display the range of possible valence electrons from one in group 1A to eight in group 8A. Representative elements display the range of possible valence electrons from one in group 1A to eight in group 8A. The valence electrons of representative elements are in s or p orbitals. The valence electrons of representative elements are in s or p orbitals. Metals tend to lose their valence electrons to form cations with a configuration of the noble gas from the preceding period Metals tend to lose their valence electrons to form cations with a configuration of the noble gas from the preceding period Nonmetals tend to gain electrons to form anins with a configuration of the noble gas in the same period Nonmetals tend to gain electrons to form anins with a configuration of the noble gas in the same period

Metalloids or semi metals

Atomic size and Group anomalies 1. H, Be, B, C, N, O & F have properties that distinguish them from their groups due to their relatively small sizes 2. H is nonmetal and forms covalent bonds; Li is metal and forms ionic bonds 3. All oxides of G 2A are ionic except that of Be (BeO) it is covalent also amphoteric. 4. Same is applicable for G 3A 5. G 5A: carbon forms readily C-C but Si forms readily Si-O 6. Si-Si exists but less stable the C-C 7. O=C=O exists but O=Si=O is not stable; Si-O-Si is stable. 8.Si does not form  bonds. Si 3p valence orbitals do not overlap with the O- 2p orbitals 2.

 bonding is important for relatively small elements of the 2 nd period. N exists as N≡N due to tendency to form  bonds P exists as P 4 ; P large atoms are like Si do not form strong  bonds. They prefer to achieve noble gas configuration but forming single bonds. O (G 6A) exists as O=O; tendency to form  bonding S does not form  bonding thus it exists as S 8. F has smaller electron affinity than Cl (not expected) the small size of F in F-F with 6 lone pairs of electrons leads to much greater repulsion compared to Cl Abundance and Preparation (P. 917): Self study

Distribution (Mass Percent) of the 18 Most Abundant Elements in the Earth's Crust, Oceans, and Atmosphere

Abundance of Elements in the Human Body

19.2 Group 1A Elements ns 1 valence electron configuration. ns 1 valence electron configuration. Comprise H and alkali metals Comprise H and alkali metals Alkali Metals

Sources and Methods of Preparation of the Pure Alkali Metals

Selected Physical Properties of the Alkali Metals Group 1: M (s) + H 2 O (l)  2M + (aq) + 2 (OH) - (aq) + H 2(g) Li has the highest ionization potential and the highest oxidation potential. Due to its small size and large energy of hydration, thus Li + attracts water effectively and large energy is released when the ion is formed. Thus formation of Li + is favored and Li behaves as a strong Reducing agent.

Types of Compounds Formed by the Alkali Metals with Oxygen

Selected Reactions of the Alkali Metals

19.3 Hydrogen Also prepared from the electrolysis of water

Hydrides Covalent hydrides Metallic/interstitial hydrides

19.4 Group 2A Elements

Group 2A Elements Ns 2 metals. They are called “Alkaline Earth metals” Ns 2 metals. They are called “Alkaline Earth metals” Their oxides are basic Their oxides are basic MO(s) + H 2 O M(OH) 2 MO(s) + H 2 O M(OH) 2 The differences in reactivity among them are shown by their reaction with water: The differences in reactivity among them are shown by their reaction with water: M(s) + 2H 2 O M(OH) 2 + H 2 (g) M(s) + 2H 2 O M(OH) 2 + H 2 (g) Ca, Ba, Sr react easily with cold water Ca, Ba, Sr react easily with cold water Mg reacts with hot water Mg reacts with hot water Be does not react with water Be does not react with water

Selected Physical Properties, Sources, and Methods of Preparation for the Group 2A Elements

BeCl 2 and BeF 2 melts are poor conductors: – –Therefore they are covalent rather than ionic solids. BeCl 2 and BeF 2

Selected Reactions of the Group 2A Elements

Ions in Natural Waters: Hard Water Rainwater is not chemically pure water. Rainwater is not chemically pure water. Contains dissolved atmospheric gases. Contains dissolved atmospheric gases. Once on the ground it may pick up a few to about 1000 ppm of dissolved substances. Once on the ground it may pick up a few to about 1000 ppm of dissolved substances. If the water contains Ca 2+ and or Mg 2+ ions we say that the water is hard. If the water contains Ca 2+ and or Mg 2+ ions we say that the water is hard. Hardness may be permanent or temporary. Hardness may be permanent or temporary.

Temporary Hard Water Contains HCO 3 - ion. Contains HCO 3 - ion. When heated gives CO 3 2-, CO 2 and H 2 O. When heated gives CO 3 2-, CO 2 and H 2 O. The CO 3 2- reacts with multivalent ions to form precipitates. (for example CaCO 3, MgCO 3 ) The CO 3 2- reacts with multivalent ions to form precipitates. (for example CaCO 3, MgCO 3 ) Water softening on a large scale is carried out by precipitating the multivalent ions using slaked lime Ca(OH) 2. CaCO 3 would be precipitated Water softening on a large scale is carried out by precipitating the multivalent ions using slaked lime Ca(OH) 2. CaCO 3 would be precipitated

Permanent Hard Water Contains significant concentrations of anions other than carbonate. Contains significant concentrations of anions other than carbonate. For example SO 4 2-, HSO 4 -. For example SO 4 2-, HSO 4 -. Usually soften by precipitating the Ca 2+ and Mg 2+ using sodium carbonate leaving sodium salts in solution. Usually soften by precipitating the Ca 2+ and Mg 2+ using sodium carbonate leaving sodium salts in solution.

Water Softening by ion-exchange Ion exchange. Ion exchange. Undesirable cations, Mg 2+ Ca 2+ and Fe 3+ are changed for ions that are not as undesirable, ex. Na +. Undesirable cations, Mg 2+ Ca 2+ and Fe 3+ are changed for ions that are not as undesirable, ex. Na +. Resins or zeolites. Resins or zeolites.

A typical cation-exchange resin. when hard water is passed over the cation-exchange resin, the ca 2+ and mg 2+ bind to the resin

19.5 Group 3A Elements ns 2 np 1 elements ns 2 np 1 elements Boron is a nonmetal that forms covalent bonds; other elements are metals Boron is a nonmetal that forms covalent bonds; other elements are metals Al forms significant covalent bonding with nonmetals; that is why Al forms significant covalent bonding with nonmetals; that is why Al 2 O 3 has amphoteric nature. Al 2 O 3 has amphoteric nature.

Selected Physical Properties, Sources, and Methods of Preparation for the Group 3A Elements

Selected Reactions of the Group 3A Elements

19.6 Group 4A Elements They have the valence electron configuration: ns 2 np 2 They have the valence electron configuration: ns 2 np 2 Contain the two most important elements on the earth, C and Si which form the basic of geologic world. Contain the two most important elements on the earth, C and Si which form the basic of geologic world. They all form covalent bonds with nonmetals: They all form covalent bonds with nonmetals: CH 4, SiF 4, GeBr 4, SnCl 4, PbCl 4 ( ِAll sp 3 hybridization) CH 4, SiF 4, GeBr 4, SnCl 4, PbCl 4 ( ِAll sp 3 hybridization)

Selected Physical Properties, Sources, and Methods of Preparation for the Group 4A Elements

Selected Reactions of the Group 4A Elements

Chapter 20 The Representative Elements: Groups 5A Through 8A

20.1 Group 5A Elements The Nitrogen Family ns 2 np 3 valence electrons configuration ns 2 np 3 valence electrons configuration Nitrogen can exist in many oxidation states. Nitrogen can exist in many oxidation states. N and P are nonmetallic. N and P are nonmetallic. As and Sb are metalloid. As and Sb are metalloid. Bi is metallic. Bi is metallic.

Bi and Sb tend to be metallic Bi and Sb tend to be metallic But no ionic compounds containing Bi 5+ and Sb 5+ are known But no ionic compounds containing Bi 5+ and Sb 5+ are known BiF 5, SbF 5 and SbCl 5 are molecular rather than ionic BiF 5, SbF 5 and SbCl 5 are molecular rather than ionic G 5A elements can form molecules or ions that involve 3, 5 or 6 covalent bonds to the G 5A atom G 5A elements can form molecules or ions that involve 3, 5 or 6 covalent bonds to the G 5A atom NH 3, PH 3, NF 3, and AsCl 3. They all behave as Lewis base. NH 3, PH 3, NF 3, and AsCl 3. They all behave as Lewis base. All G 5A elements except N can form molecules (MX 5 ) with 5 covalent bonds. All G 5A elements except N can form molecules (MX 5 ) with 5 covalent bonds. The ability of G 5A elements to form  bonds decreases dramatically after N. The ability of G 5A elements to form  bonds decreases dramatically after N. This is why N exists as N 2 molecules; while other elements in the group exist as larger aggregates containing single bonds: P 4, As 4, Sb 4 This is why N exists as N 2 molecules; while other elements in the group exist as larger aggregates containing single bonds: P 4, As 4, Sb 4

The Molecules of the Types MX 3, MX 5, and MX 6 Formed by Group 5A Elements

The Structures of the Tetrahedral MX 4 + and Octahedral MX 6 - Ions

20.2 The Chemistry of Nitrogen Since N 2 molecule contains a triple bond, most binary compounds (except NH 3 ) containing N decompose exothermically to the elements Since N 2 molecule contains a triple bond, most binary compounds (except NH 3 ) containing N decompose exothermically to the elements In the preparation of NH 3 from N 2 and H 2, too much energy is needed to disrupt the N≡N bond. In the preparation of NH 3 from N 2 and H 2, too much energy is needed to disrupt the N≡N bond. Thus, though K (10 6 ) is high the reaction is very slow at room temperature. Thus, though K (10 6 ) is high the reaction is very slow at room temperature. Haber process is used to prepare NH 3 (high pressure, high temperature and a catalyst are needed) Haber process is used to prepare NH 3 (high pressure, high temperature and a catalyst are needed) Nitrogen fixation: The process of transforming N 2 to other nitrogen containing compounds Nitrogen fixation: The process of transforming N 2 to other nitrogen containing compounds

Nitrogen fixation can be carried out by: Nitrogen fixation can be carried out by: Haber process (ammonia can be applied to the soil as a fertilizer) Haber process (ammonia can be applied to the soil as a fertilizer) High temperature combustion process in automobile engines. NO produced is converted into NO 2 that with moisture is concerted into NO 3 - that reaches soil. High temperature combustion process in automobile engines. NO produced is converted into NO 2 that with moisture is concerted into NO 3 - that reaches soil. Natural. Lightning produces the energy that disrupt N 2 and O 2 molecules producing reactive N and O atoms that attack other molecules to form nitrogen oxides that convert eventually to NO 3 - Natural. Lightning produces the energy that disrupt N 2 and O 2 molecules producing reactive N and O atoms that attack other molecules to form nitrogen oxides that convert eventually to NO 3 - Nitrogen-fixing bacteria that reside on the root of nodules of plants such as beans and peas. This converts N 2 to ammonia and other nitrogen containing compounds. Nitrogen-fixing bacteria that reside on the root of nodules of plants such as beans and peas. This converts N 2 to ammonia and other nitrogen containing compounds. Denitrification: return of N element to the atmosphere as N 2 gas. Bacteria changes NO 3 - to N 2 Denitrification: return of N element to the atmosphere as N 2 gas. Bacteria changes NO 3 - to N 2

The Nitrogen Cycle

Some Common Nitrogen Compounds

20.3 The Chemistry of Phosphorus Chemical properties of P are significantly different from N for the following reasons: Chemical properties of P are significantly different from N for the following reasons: Nitrogen’s stability to form much stronger  bonds Nitrogen’s stability to form much stronger  bonds Grater electronegativity of N Grater electronegativity of N Larger size of P atom Larger size of P atom Availability of empty valence d orbitals on P Availability of empty valence d orbitals on P White phosphorus exists as P4: very reactive and bursts into flames on contact with air. White phosphorus exists as P4: very reactive and bursts into flames on contact with air. It is commonly stored under water It is commonly stored under water Black P and Red P are network solids Black P and Red P are network solids

( a) The P 4 Molecule Found in White Phosphorus (b) The Crystalline Network Structure of Black Phosphorous (c) The Chain Structure of Red Phosphorus

P is essential for plant growth P is essential for plant growth Soluble phosphate fertilizer is made by treating phosphate rock with sulfuric acid to make superphosphate of lime, that is a mixture of : Soluble phosphate fertilizer is made by treating phosphate rock with sulfuric acid to make superphosphate of lime, that is a mixture of : CaSO 4. 2H 2 O and Ca(H 2 PO 4 )2. H 2 O CaSO 4. 2H 2 O and Ca(H 2 PO 4 )2. H 2 O A reaction of NH3 and P produces NH 4 H 2 PO 4 A reaction of NH3 and P produces NH 4 H 2 PO 4 a very efficient fertilizer a very efficient fertilizer

20.4 The Group 6A Elements The valence electron configuration is ns 2 np 4 The valence electron configuration is ns 2 np 4 Non of these elements behaves as a metal Non of these elements behaves as a metal They achive the noble gas configuration by adding 2 electrons to become 2 - anion They achive the noble gas configuration by adding 2 electrons to become 2 - anion G 6A elements can form covalent bonds with other nonmetals G 6A elements can form covalent bonds with other nonmetals Due to the presence of empty d orbitals (except O), they form molecules in which central atom is surrounded by more than 8 electrons: SF 4 and SF 6 Due to the presence of empty d orbitals (except O), they form molecules in which central atom is surrounded by more than 8 electrons: SF 4 and SF 6

Group 7A ns2 np5 valence electron configuration. ns2 np5 valence electron configuration. All nonmetals All nonmetals Reactive. Not free in nature. Found as halide (X - ) ions. Reactive. Not free in nature. Found as halide (X - ) ions. Astatine radioactive with t 1/2 = 8.3 hrs for its longest living isotope Astatine radioactive with t 1/2 = 8.3 hrs for its longest living isotope Very high electronegativities (4, 3, 2.8, 2.5 and 2). Very high electronegativities (4, 3, 2.8, 2.5 and 2). Ionic bonds with metals and covalent bonds with nonmetals in low oxidation states & polar covalent in metals in high oxidation states. Ionic bonds with metals and covalent bonds with nonmetals in low oxidation states & polar covalent in metals in high oxidation states.

Hydrogen Halides HCl is the most important acid. HCl is the most important acid. HF is used for etching glass. HF is used for etching glass. SiO 2 (s) + 4HF(aq)  SiF 4 (g) + 2H 2 O(l)

Group 8A ns 2 p 6 configuration; Un-reactive. ns 2 p 6 configuration; Un-reactive. He. Component of the sun. He. Component of the sun. Present in natural gas (from decay of radioactive elements). Present in natural gas (from decay of radioactive elements). Used as Coolant and a rocket pressurizing gas. Used as Coolant and a rocket pressurizing gas. Ne. Used in Luminescent lighting. Ne. Used in Luminescent lighting. Ar. Used as a non-corrosive atmosphere in light bulbs. Ar. Used as a non-corrosive atmosphere in light bulbs. Xe & Kr form compounds with O and F. Xe & Kr form compounds with O and F.