Trends in Period 3

M+X-ionic bond, M+-X+polar bondandM-X a relatively non-polar bond(no partial charges shown)ElementSodiumMagnesiumAluminiumSiliconPhosphorusSulfurChlorineArgon

old/latestGroup123/134/145/156/167/170/18

ZSymbol11Na12Mg13Al14Si15P16S17Cl18Ar

Structure of elementsolid metallic lattice of Na+and free e-solid metallic lattice of Mg2+and free e-solid metallic lattice of Al3+and free e-solid giant covalent lattice Sinsolid small covalent molecules P4solid small covalent molecules S8gaseous small covalent molecules Cl2gaseous single atoms

electron configuration[Ne]3s1[Ne]3s2[Ne]3s23p1[Ne]3s23p2[Ne]3s23p3[Ne]3s23p4[Ne]3s23p5[Ne]3s23p6

common oxidation statese.g. in oxides, chlorides, hydrides+1max +1+2max +2+3max +3+4max +4+3, +5max +5-2, -2, +4, +6max +6-1, +1, +3, +5, +7max +7at Xe can get max of +8 compounds but not here!

electronegativity of element0.931.311.611.902.192.583.163.20

formula of oxidesNa2O, Na2O2MgOAl2O3SiO2P4O6, P4O10SO2, SO3Cl2O,ClO2,Cl2O6, Cl2O7-

bonding and structure of oxidesionic latticeionic latticeionic latticesolid covalent giant structuresolid covalent small moleculescovalent small gaseous moleculescovalent small gas/liquid molecules-

electronegativity difference X-O (O is 3.44) nature of bond2.51Na+O2-orO22-2.13Mg2+O2-1.83Al3+O2-1.54Si+-O-1.25P+-O-0.86S+-O-0.28Cl-O-

formula of chloridesNaClMgCl2AlCl3SiCl4PCl3, PCl5S2Cl2, ??Cl2-

bonding in chloridesionic latticeionic latticeionic lattice, vaporises to covalent dimer molecules Al2Cl6covalent small liquid moleculesliquid covalent small moleculescovalent small liquid moleculescovalent small diatomic gaseous molecule-

electronegativity difference X-Cl (Cl is 3.16) nature of bond2.23Na+H-1.85Mg2+Cl-1.55Al3+Cl-1.26Si+-Cl-1.25P+-Cl-0.58S+-Cl-0.00Cl-Cl-

Formula of hydrideNaHMgH2AlH3SiH4PH3H2SHCl-

bonding and structure of hydrideionic lattice'polymer-like' structure of intermediate ionic/covalent nature'polymer-like' structure of intermediate ionic/covalent naturesmall covalent gaseous moleculesmall covalent gaseous moleculesmall covalent gaseous moleculesmall covalent gaseous molecule-

electronegativity difference X-H (H is 2.20) nature of bond1.27Na+H-0.89Mg+-H-0.59Al+-H-0.30Si-H0.01P-H0.38H+-S-0.96H+-Cl--

The structure and physical properties of the elements The trend is metal lattice ==> giant covalent structure ==> small covalent molecules Sodium Na, magnesium Mg and aluminium Al are silvery solids, with a metal lattice structure, high boiling points and are good conductors of heat/electricity due to the delocalised free electrons moving between the immobile metal ions. The melting/boiling points increase from Na ==> Mg ==> Al due to 1 ==> 2 ==> 3 potential number of delocalised electrons that may contribute to bonding. Si has a non-metallic giant covalent structure based on a tetrahedral arrangement of S-Si bonds and is a poor conductor of heat/electricity. The strong 3D bonding gives silicon a high melting/boiling point and great hardness. Phosphorus P4, sulfur S8and chlorine Cl2are simple-small covalent molecules and Ar consists of single atoms. The molecules are only held together by the weakest of the intermolecular forces, namely the instantaneous dipole - induced dipole forces, and consequently have very low melting/boiling points. From left to right the elements become less metallic and more non-metallic. - Electron configuration and oxidation states Electron configurationsof 2,8,1 or1s22s22p63s1to 2,8,8 or1s22s22p63s23p6 Filling the s orbital (max 2 e-'s) gives the metallic s-block elements of Groups 1-2, filling the p orbitals gives the predominantly non-metallic p block elements of Group 3-7, 0 (Gps 13-18) bar aluminium for Period 3. Oxidation statesin compounds (numerically = valency) are: sodium Na (+1 only), magnesium Mg (+2 only), aluminium Al (+3 only), Si (+4, -4 with electropositive metals), P (usually -3, +3 or +5), S (-2, +4 and +4), Cl (-1, +1, +3, +5 and +7), Ar has no stable compounds due to the full outer quantum level (shell) being full, conferring extra electronic stability on the atom. From Na to Cl the maximum oxidation state is equal to the 'old' group number and the 'highest' oxide formulae can be predicted up to chlorine and the chloride formula up to P (there is no stable SCl6but there is a ClF7. So in the 'highest' oxides you can go from +1 to +7 for groups 1 to 7/17 (at Xe on Period 5 you can reach +8, but not for Ar) Na2O, MgO, Al2O3, SiO2, P4O10(= P2O5), SO3, Cl2O7(at Xe you can have XeO4) i.e. using all available 1-7 outer 3s and 3p electrons (valence electrons) are all used in the bonding of the highest possible oxide. and similarly in the 'highest' chlorides (upto Group 5), and fluorides (for Groups 6 and 7) you also go from maximum oxidation state of +1 to +7 in the halide compounds irrespective of bond character. NaCl, MgCl2, AlCl3, SiCl4, PCl5, SF6, ClF7(at Xe you can have XeF8) - Reaction of element with oxygen and the structure of the oxide(Gp 1)4Na(s)+ O2(g)==>2Na2O(s)and Na2O2on heating the metal in air(Gp 2)2Mg(s)+ O2(g)==>2MgO(s)on heating metal in air

(Gp 3)4Al(s)+ 3O2(g)==>2Al2O3(s)needs high temperature(Gp 4)Si(s)+ O2(g)==> SiO2(g)needs high temperature

(Gp 5)P4(s)+ 5O2(g)==> P4O10(s)on heating in air(Gp 6)S(s)+ O2(g)==> SO2(g)and a little SO3on heating in air

(Gp 7) Chlorine - no reaction(Gp 0) Argon - no reaction

Reaction with oxygen and oxide structure The metals Na, Mg and Al burn to form a giant ionic oxide lattices sodium oxide/peroxide, magnesium oxide and aluminium oxide ... (Na+)2O2-and (Na+)2O22-, Mg2+O2-and (Al3+)2(O2-)3respectively. Silicon Si forms a giant covalent lattice of (SiO2)nwhere n is very larger number Phosphorus P forms two simple molecular covalent solid oxides P4O6and P4O10. Sulphur/sulfur S can form two simple molecular covalent gas molecules SO2and SO3 Chlorine Cl forms oxide molecules of Cl2O, Cl2O7(and others). Argon has no reaction. The overall pattern, fromleft to right is giant ionic lattice => giant covalent lattice ==> small covalent molecules. The change in bonding character from ionic to covalent in the oxide, follows the decreasing difference in electronegativity between that of the period 3 element and oxygen. - Reaction of the oxides with water, acids and alkalis(Gp 1)Na2O(s)+ H2O(l)==>2NaOH(aq)pH 13-14 strong baseorNa2O2(s)+ 2H2O(l)==> 2NaOH(aq)+ H2O2(aq)(Gp 2)MgO(s)+ H2O(l)==>Mg(OH)2(aq/s)~pH 11-12 weak base

(Gp 3)Al2O3, insoluble, no reaction with water, but amphoteric with respect to acids and strong alkalis(Gp 4) SiO2, insoluble, no reaction with water, but weakly acidic and will dissolve a little in strong alkali e.g. conc. NaOH(aq)

(Gp 5)P4O6(s)+ 6H2O(l)==> 4H3PO3(aq)~pH 2 weak acidP4O10(s)+ 6H2O(l)==> 4H3PO4(aq)pH 1 strong acid(Gp 6)SO2(aq)+ H2O(l) H+(aq)+ HSO3-(aq)pH 2-3 weak acidSO3(g)+ H2O(l)==> H2SO4(aq)pH 0-1 strong acid

(Gp 7)Cl2O(g)+ H2O(l)==>2HClO(aq)~pH 3? weak acidCl2O7(l)+ H2O(l)==> 2HClO4(aq)pH 1 strong acid(Gp 0) argon has no oxide

The chemical character of the oxides - reaction of the Period 3 oxides with water, acids or alkalis. Sodium oxide/peroxideNa2O/Na2O2andmagnesium oxideMgO are basic and form an alkali in water and salts with acids. MgO(s) + 2HCl(aq) ==> MgCl2(aq) + H2O(l) Aluminium oxide Al2O3has no reaction, insoluble, but isamphotericand forms salts with acids and alkalis. Al2O3(s) + 6HCl(aq) ==> 2AlCl3(aq) + 3H2O(l) Al2O3(s)+ 2NaOH(aq)+ 3H2O(l)==>2Na[Al(OH)4](aq) Silicon(IV) oxide(silicon dioxide) SiO2has no reaction but is weakly acidic forming salts with alkalis. Phosphorus(III) oxideP4O6andphosphorus(V) oxideP4O10are moderately-strong acidic oxides forming phosphoric(III) acid H3PO3and phosphoric(V) acid H3PO4on reaction with water. Generally speaking, in a series of oxides for the same element, the higher the oxidation state of X in a 'XxOy' series, the more acidic is the oxide, so H3PO4is a stronger acid than H3PO3. The oxides or acids are readily neutralised to give phosphate salts e.g. H3PO4(aq) + NaOH(aq) ==> NaH2PO4(aq) + H2O(l) Two further reactions are possible with the sodium hydroxide to giveNa2HPO4andNa3PO4. Chlorine(I) oxide Cl2O and chlorine(VII) oxide Cl2O7are moderate to strong acidic in water. The overall patterns, fromleft to right across Period 3 is ... giant ionic lattice ==> small covalent molecules The change in bonding character from ionic to covalent in the oxide follows the decreasing difference in electronegativity between that of the element and oxygen. In terms of overall chemical character ... metal basic oxides ==> amphoteric oxides ==> non-metal oxides This is chemically characteristic ofmetallic ==> non-metallic element character. - Reaction of element with chlorine and the structure of the chloride(Gp 1)2Na(s)+ Cl2(g)==>2NaCl(s)(Gp 2)Mg(s)+ Cl2(g)==>MgCl2(s)

(Gp 3)2Al(s)+ 3Cl2(g)==> 2AlCl3(s)(Gp 4)Si(s)+ 2Cl2(g)==> SiCl4(l)

(Gp 5)P4(s)+ 3Cl2(g)==> 4PCl3(l)P4(s)+ 5Cl2(g)==> 4PCl5(s)(Gp 6)2S(s)+ Cl2(g)==> S2Cl2(l)also unstable SiCl2, SiCl4

(Gp 7) chlorine itself(Gp 0) no reaction with argon

Reaction with chlorine and chloride structure All of Na to S will combine directly on heating in chlorine to give the chloride. Sodium, magnesium and aluminium give giant ionic lattices sodium chloride Na+Cl-, magnesium chloride Mg2+(Cl-)2and aluminium chloride Al3+(Cl-)3respectively. Note that aluminium chloride on heating sublimes above 180oC to form small Al2Cl6covalent dimer molecules. The non-metal elements give covalent chlorides. Silicon forms the molecular covalent liquid silicon(IV) chloride SiCl4(silicon tetrachloride) Phosphorus formsphosphorus(III) chloridePCl3(phosphorus trichloride) with limited chlorine andphosphorus(V) chloridePCl5(phosphorus pentachloride) with excess chlorine. Sulphur givesdisulfur dichlorideS2Cl2. by direct combination (and unstable SCl2and SCl4can also be formed). There is no stable argon chloride. The overall pattern, fromleft to right across period 3 is ... giant ionic lattice =>polymeric covalent lattice==> small covalent molecules. This is chemically characteristic of metallic ==> non-metallic element character. The change in bonding character from ionic to covalent in the chloride, follows the decreasing difference in electronegativity between that of the element and oxygen, as in the case of oxides. The formulae largely follow a pattern of rising formulae based on the use ofallouter electrons in bonding (1-5) and then a decline in valency (oxidation state of the Period 3 element). NaCl(+1),MgCl2(+2),AlCl3(+3),SiCl4(+4),PCl5(+5),S2Cl2(+1),Cl2,Arno chloride So the number of atoms of chlorine combined with the Period 3 element (the valency) follows the pattern 1 2 3 4 5 1 1 0 - Reaction of the chlorides with water(Gp 1)NaCl(s)+ aq==>Na+(aq)+ Cl-(aq)just dissolves, ~pH 7(Gp 2)MgCl2(s)+ aq ==> Mg2+(aq)+ 2Cl-(aq)just dissolves, ~pH 7

(Gp 3)AlCl3(s)+ 3H2O(l)==>Al(OH)3(s)+ 3HCl(g)with limited water you get hydrolysis to give acid fumesAlCl3(s)+ aq==>Al3+(aq)+ 3Cl-(aq)excess water, weakly acidic solution due to the acidity of [Al(H2O)6]3+(Gp 4)SiCl4(l)+ 2H2O(l)==> SiO2(s)+ 4HCl(aq)hydrolysis to give strongly acid solution

(Gp 5)PCl3(l)+ 3H2O(l)==> H3PO3(aq)+ 3HCl(aq)hydrolysis to give weakly acid solutionPCl5(s)+ 4H2O(l)==> H3PO4(aq)+ 5HCl(aq)hydrolysis to give strongly acid solution(Gp 6)S2Cl2(g)+ H2O(l)==> HCl(aq), S(s), SO2(aq), H2SO3(aq), H2SO4(aq),H2S(aq)-complex redox/hydrolysis reaction but final solution is quite acidic

(Gp 7) chlorine itselfGp 0 argon has no chloride

Reaction of the chloride with water Theionicsodium chloride NaCl and magnesium chloride MgCl2dissolve in water to form a nearly neutral solution of hydrated ions. Theionic AlCl3and the covalentall hydrolyse to form acid solutions. aluminium chloride Al2Cl6==> hydrochloric acid or weakly acidic aluminium ion silicon(IV) chloride SiCl4, (silicon tetrachloride) ==> hydrated silicon dioxide + hydrochloric acid phosphorus(III) chloride PCl3(phosphorus trichloride) ==> phosphoric(III) acid + hydrochloric acid with phosphorus(V) PCl5(phosphorus pentachloride) ==> phosphoric(V) acid + hydrochloric acid Phosphorus(III) chloride hydrolyses rapidly and exothermically to form phosphoric(III) acid. PCl3(l)+ 3H2O(l)==> H3PO3(aq)+ 3HCl(aq) Phosphorus(V) chloride initially hydrolyses to form phosphorus oxychloride and hydrochloric acid. (i)PCl5(s)+ H2O(l)==> POCl3(aq)+ 2HCl(aq) If the aqueous solution is boiled, phosphoric(V) acid is formed and more hydrochloric acid. (ii)POCl3(aq)+ 3H2O(l)==> H3PO4(aq)+ 3HCl(aq) overall (i) + (ii):PCl5(s)+ 4H2O(l)==> H3PO4(aq)+ 5HCl(aq) and disulphur dichloride S2Cl2==> a variety products including acidic sulphur dioxide and hydrochloric acid. The general trend is for ionic metal chloride salts to give nearly neutral solutions => metal/non-metal covalent chlorides that hydrolyse to give acidic solutions.- Reaction of element with water(Gp 1)2Na(s)+ 2H2O(l)==>2NaOH(aq)+ H2(g)(Gp 2)Mg(s)+ 2H2O(l)==> Mg(OH)2(aq)+ H2(g)

(Gp 3) aluminium has no reaction with water(Gp 4) silicon has no reaction with water

(Gp 5) phosphorus has no reaction with water(Gp 6) sulfur has no reaction with water

(Gp 7)Cl2(g)+ H2O(l) HClO(aq)+ HCl(aq)(Gp 0) argon has no reaction with water

Reaction of element with water The reactive metal sodium Na rapidly gives the alkaline sodium hydroxide and hydrogen, as does magnesium Mg BUT much more slowly. Aluminium Al, silicon Si, phosphorus P and sulfur S have no reaction with water. Chlorine, Cl2forms a weakly acidic solution in water. Argon has no reaction. The 'limited'pattern for period 3 (or any other period), is to have reactive metals on the left forming an alkaline solution and a reactive non-metal on the right forming an acid solutions IF they react with water. - The hydridesMHx For hydrides the difference in electronegativity works both ways! From left to right across the period you change from an ionic sodium hydride crystal lattice Na+H- to small non-polar molecule covalent hydrides (silane SiH4and phosphine PH3) and then a weakly acidic polar covalent hydride molecule (hydrogen sulfide H2S) and finally a strongly acidic polar covalent molecule (hydrogen chloride HCl). The formulae follow a simple period pattern of rising and falling valency for the Period 3 elements. NaH MgH2 AlH3 SiH4 PH3H2S HCl (Ar) the element valency pattern being1 2 3 4 3 2 1 0 On reaction with water, the ionic metal hydrides at the start of the period give an alkaline solution e.g.NaH(s)+ H2O(l)==> NaOH(aq)+ H2(g) In the middle are neutral hydrides like phosphine which in contact with water do not change the pH. Then you get weakly acidic ==> strongly acidic hydrides when they dissolve in water e.g. weak acid:H2S(aq)+ H2O(l) H3O+(aq)+ HS-(aq) strong acid:HCl(aq)+ H2O(l)==> H3O+(aq)+ Cl-(aq) So things are a bit complicated with hydrides on period 3 due to the left and right sided differences in electronegativity! You go fromX+H-==> X+-H ==> X-H ==> X-H+ - Radii of isoelectronic ions Isoelectronic means species having the same total number of electrons. The table below considers the isoelectronic cations and anions associated with Periods 2, 3 and 4. isoelectronic systemGroup 4/14Group 5/15Group 6/16Group 7/17(Group 0/18)Group 1Group 2Group 3/13

PeriodPeriod 2Period 3

[Ne] 10e 1s22s22p6C4-N3-O2-F-(Ne)Na+Mg2+Al3+

total nuclear charge+6+7+8+9(+10)+11+12+13

radius in picometre (pm)260171140136(38-112*)956550

name of ioncarbidenitrideoxidefluoride(neon)sodiummagnesiumaluminium

PeriodPeriod 3Period 4

[Ar] 18e 1s22s22p63s23p6Si4-P3-S2-Cl-(Ar)K+Ca2+Sc3+

nuclear charge+14+15+16+17(+18)+19+20+21

radius in picometre (pm)271212184181(71-154*)1339981

name of ionsilicidephosphidesulfidechloride(argon)potassiumcalciumscandium

Excluding the noble gases themselves where this is frankly, something of a data problem!, there is a clear pattern of decreasing ionic radius with increase in total nuclear charge (+ atomic/proton number) for the two isoelectronic series tabulated above, based on the electron configurations of neon and argon.