Group Trends for Metals and Nonmetals

Noble Gases

Chapter 8

 

Alkali metals

Alkali metals – combine directly with most nonmetals

            M _(s) + S _(s) → M₂S _(s)

            M _(s) + Cl_{2 (g)} → 2MCl _(s)

            M _(s) + H_{2 (g)} → 2MH

                        NaH     H^-  hydride ion

                                    (H⁺ hydrogen ion)

Alkali metals react vigorously with H₂O

            2M _(s) + 2H₂O _(l) → 2MOH _(aq) + H_{2 (g)}

Alkali metals react directly with O₂:

            4Li _(s) + O_{2 (g)} → 2Li₂O _(s)

            2Na _(s) + O_{2 (g)} → Na₂O_{2 (s)}

                                       sodium peroxide

                                         (Na₂O + O₂)

            K, Rb, Cs → superoxides O₂^-

            KO_{2 (s)}              RbO_{2 (s)}            CsO_{2 (s)}

            O in –½ oxidation state

Alkali metals stored under mineral oil or kerosene (exclude O₂, H₂O)

Flame Tests:     Li – red

                        Na – yellow

                        K – purple

 

Alkaline Earth Elements

Solids, harder, more dense, higher melting points than alkali metals

First ionization energies > those of alkali metals

            Less reactive

React with H₂O

            Mg _(s) + H₂O _(g) (steam) → MgO _(g) + H_{2 (g)}

            Ca _(s) + 2H₂O _(l) → Ca(OH)_{2 (aq)} + H_{2 (g)}

            Mg _(s) + Cl_{2 (g)} → MgCl_{2 (s)}

            2Mg _(s) + O_{2 (g)} → 2MgO _(s)

Heavier alkaline earth elements Ca, Sr, Ba react with nonmetals – stored to exclude O₂ and H₂O

Flame tests:      Ca – brick red

                        Sr – crimson red

                        Ba – green

 

Group Trend Selected Nonmetals

H         H_{2 (g)}     electron configuration of 1s¹

High first ionization energy (I₁): 1312 kJ/mole

React with nonmetals → molecular compounds

2H_{2 (g)} + O_{2 (g)} → 2H₂O _(l)                    ∆H° = -571.5 kJ

            highly exothermic

metal hydrides

            2Na _(s) + H_{2 (g)} → 2NaH _(s)

 

Group 6A Oxygen Group

O         O_{2 (g)}

S, Se nonmetals, solids

Te metalloid

Po (polonium) – radioactive, rare, metal

O₂        O₃ (ozone) – allotropes – different forms of same element in same state

O₂ ≈ 21% air

O₃ – toxic, pungent odor

            Present in small amounts in upper atmosphere

            Absorb UV radiation from sun

            (protective)

O₃ forms from O₂ in electrical discharges

            Less stable than O₂

O₂ will oxidize many metals

Stable oxide ion – O^2-

            Noble gas configuration

Peroxides – O₂^2-

            Less stable

            2H₂O_{2 (l)} → 2H₂O _(l) + O_{2 (g)}

                        disproportionation

                        O^-1       oxidized to O₂

                                    Reduced to O^2-

S allotropic forms – S₈ – 8-member ring of S atoms – written as S _(s)

S^2- – sulfide ion – most sulfur exists as metal sulfide

S burns in O₂ → SO₂ pollutant

 

Group 7A Halogens

F₂, Cl₂, Br₂, I₂              At – astatine

                                    Rare, radioactive

                                    Properties largely unknown

Halogens have high electron affinities – strongly attract electrons

            X₂ + 2e^- → 2X^-            X = halogen

F, Cl more reactive than Br, I

            2Na _(s) + F_{2 (g)} → 2NaF _(s)        ∆H° = -1147 kJ

F dangerous to use in lab – highly reactive

Cl most useful industrially – produces electrolyte NaCl

            Cl_{2 (g)} + H₂O _(l) → HCl _(aq) + HOCl _(aq)

            H_{2 (g)} + X₂ (halogen) → 2HX _(g)

            Hydrogen halides water soluble → acids (HF weak acid)

 

Group 8 Noble Gases

Gases at room temperature

Monatomic

Radon (Rn) radioactive, carcinogenic

Completely filled s and p subshells

Large I₁ values

Stable electron configurations – very nonreactive

Formerly were considered “inert”

            Believed not to react at all

Bartlett (1962) proposed I₁ of Xe low enough to allow it to form compounds with F – high ability to remove electrons from other substances

            Synthesized a number of compounds of Xe and F – XeF₂, XeF₄, XeF₆

Kr not as reactive as Xe, but will form 1 compound with F – KrF₂

He, Ne, Ar – no known compounds

 

Chapter 8 Basic Concepts of Chemical Bonding

Ionic bonding – results from transfer of electrons from one atome to another

            Interaction of metals and nonmetals

            NaCl

Covalent bonding – sharing of electrons between 2 atoms

            Nonmetallic elements – results in molecular compounds

Metallic bonds – solid metals Cu, Fe, Al

            Metal atoms bonded to neighboring metallic atoms

            Electrical conductivity, luster