The Representative Elements Ch 20 Representative Elements Their

The Representative Elements Ch 20

Representative Elements • Their chemical properties are determined by their valence (s and p) electrons. • Properties are similar within a group, but first element in a group tends to act differently due to smaller size. • Most abundant element is oxygen, followed by silicon. • Most abundant metals are aluminum and iron, which are found as ores.

Group 1 (1 A) – Alkali Metals • Have Valence electron configuration ns 1 • Will lose 1 electron to form M+ Ions • React vigorously with water to form M+ and OH- ions and hydrogen gas. • React with oxygen to form oxides. Lithium will form a regular oxide (Li 2 O) while sodium will form a peroxide (Na 2 O 2). Potassium, rubidium and cesium form superoxides (MO 2)

Selected Reactions of the Alkali Metals Reaction Comment 2 M + X 2 2 MX X 2 = any halogen molecule 4 Li + O 2 2 Li 2 O Excess oxygen 2 Na + O 2 Na 2 O 2 M + O 2 MO 2 M = K, Rb or Cs 2 M + S M 2 S 6 Li + N 2 2 Li 3 N Li only 12 M + P 4 4 M 3 P 2 M + H 2 2 MH 2 M + 2 H 2 O 2 MOH + H 2 2 M + 2 H+ 2 M+ + H 2 Violent reaction!

Hydrogen • Can form covalent compounds with other nonmetals. • Will form salts, hydrides, with very active metals (group 1 A and 2 A). • Hydride ion, H-, is a strong reducing agent. • Covalent hydrides form when hydrogen bonds with other nonmetals. • Metallic hydrides occur when hydrogen atoms migrate into transition metal crystals.

Group 2 (2 A) – Alkaline Earth Metals • Have valence electron configuration ns 2 • Called Alkaline earth because of the basicity of their oxides. • React less vigorously with water than group 1. • Heavier alkaline earth metals form ionic nitrides and hydrides. • Hard water is caused by the presence of Ca+2 and Mg+2 ions.

Selected Reactions of the Alkaline Earth Metals Reaction Comments M + X 2 MX 2 = any halogen molecule 2 M + O 2 2 MO Ba gives Ba. O 2 as well M + S MS 3 M + N 2 M 3 N 2 High temperatures 6 M + P 4 2 M 3 P 2 High temperatures M + H 2 MH 2 M = Ca, Sr or Ba; high temperatures; Mg also needs high pressure M + 2 H 2 O M(OH)2 + H 2 M = Ca, Sr or Ba M + 2 H+ M+2 + H 2 Be + 2 OH- + 2 H 2 O Be(OH)42 - + H 2

Group 13 (3 A) • Have valence electron configuration ns 2 np 1 • Show increasing metallic character going down the group. • Boron forms covalent compounds with hydrides called boranes. These compounds are highly electron deficient and very reactive. • Aluminum has some covalent characteristics as do indium and gallium. • Thallium is completely metallic in character.

Selected Reactions for Group 13 (3 A) Elements Reactions Comments X 2 = any halogen molecule; Tl gives Tl. X as well but no Tl. I 3 2 M + 3 X 2 2 MX 3 High temperatures; Tl gives Tl 2 O as well 4 M + 3 O 2 2 M 2 O 3 High temperatures; Tl gives Tl 2 S as well 2 M + 3 S M 2 S 3 M = Al only 2 M + N 2 2 MN 2 M + 6 H+ 2 M + 2 OH- 2 M 3+ M = Al, Ga or In; Tl gives Tl+ + 3 H 2 + 6 H 2 O 2 M(OH)4 - + 3 H 2 M = Al or Ga

Group 14 (4 A) • Have valence electron configuration ns 2 np 2 • Show a change from nonmetallic to metallic properties going down the group. • All elements in this group form covalent bonds with nonmetals. • MX 4 compounds (except carbon)react with Lewis bases to form two additional covalent bonds.

Selected Reactions of the Group 14 (4 A) Elements Reactions Comments M + 2 X 2 MX 4 X 2 = any halogen molecule; M = Ge, or Sn; Pb gives Pb. X 2 M + O 2 MO 2 M = Ge, or Sn; high temperatures; Pb gives Pb. O or Pb 3 O 4 M + 2 H+ M 2+ + H 2 M = Sn or Pb

Group 15 (5 A) • Have varied chemical properties. • All members except nitrogen form molecules with 5 covalent bonds. (Nitrogen has no d sublevel) • Nitrogen and Phosphorous are nonmetals and form 3 - anions in salts with active metals. • Antimony and bismuth are metallic. However their 5+ cations tend to be molecular rather than ionic.

Nitrogen • The strength of the triple bond in the N 2 molecule is important both thermodynamically and kinetically as they decompose exothermically. • The nitrogen cycle is the process through which nitrogen is recycled through the environment. • Nitrogen forms a series of oxides in which it has an oxidation state ranging from 1 to 5. • Nitric acid is a strong acid which is important as a reducing agent. • Ammonia is the most important nitrogen hydride. • Has pyramidal molecules with polar bonds. • Hydrazine (N 2 H 4) is a powerful reducing agent.

Phosphorous • Exists in three elemental forms: white, black and red. • Phosphine (PH 3) has a structure analogous to that of ammonia but with bond angles closer to 90 o. • Forms two oxides with oxidation states of 3+ and 5+.

Group 16 (6 A) • Shows the usual tendency of increasing metallic properties going down the group. • None behave as typical metals • Achieve noble gas configurations by adding two electrons to form 2 - anions. • Form covalent bonds with other nonmetals. • Oxygen exists in two elemental forms: O 2 and O 3. • Sulfur has two elemental forms, both of which contain stacks of S 8 rings. • Sulfur also forms two oxides: SO 2 and SO. • Sulfur forms a variety of compounds in which it has a +6, +4, +2, 0 or -2 oxidation state.

Group 17 (7 A) - Halogens • This group consist of all nonmetals. • Form hydrogen halides (HX) that behave as strong acids in water, except for hydrogen fluoride. • Oxyacids of the halogens become stronger as the number of oxygen atoms attached to the halogen increase. • Interhalogens are compounds of two different halogens • Halogen-carbon compounds are important industrially: examples are Teflon, PVC and the Freons.

Group 18 (8 A) – Noble Gases • Full valence shells ns 2 np 6 • Generally unreactive. • Krypton, xenon and radon will form compounds with the highly electronegative elements fluorine and oxygen.

Transition Elements Ch 21

The last electron in transition metals occupy the d sublevel. Because these inner orbitals cannot participate as easily in bonding as the s and p orbitals the chemistry is not greatly affected by the gradual change in the increased number of electrons in the d orbital.

• Have metallic physical and chemical properties. • In forming ionic compounds with nonmetals, the transition metals exhibit several typical characteristics: • More than one oxidation state is usually found • Cations are often complex ions • Most compounds are colored • Most compounds have paramagnetic properties

• Transition metals form a variety of ions by losing one or more of their electrons. • The maximum possible oxidation state for a given transition element corresponds to the loss of all the s and d electrons. • Transition metals form coordination compounds which consist of complex ions and counter ions. • These coordination complexes are very important to biological chemistry.

Naming Coordination Compounds • The cation is named before the anion • The ligands are named before the metal ion • An o is added to the root name of an anion in the ligand • Prefixes are used to denote the number of simple ligands • The oxidation state of the central metal ion is designated by a Roman numeral in parenthesis • If more than one ligand is present, name them alphabetically (prefixes do not count) • If complex ion has a negative charge, the suffix –ate is added to the name of the metal