PERIOD 3 ELEMENTS
Physical properties
Atomic size
atomic radius = covalent radius [van der Waals radius > covalent radius]


-Atomic radius
depends on +ve nuclear charge attraction & screening/shielding effect
-positive nuclear charge attraction: bet protons in nucleus and valence e^-s (more protons > more attraction > smaller radius)
-screening effect of inner filled e- shells: inner e-s repel each other > screen off some nuclear charge attraction > greater radius (more inner filled shells > more repulsion > greater radius)

Period 3 atomic radii
all elements: same # of inner filled quantum shells > roughly same screening effect
across period: proton # increase > more attraction > smaller radii
argon: great increase due to use of van der Waal radius- Ar atoms separated by relatively large dist > large radius


-Ionic radius

radii of +ve ions smaller than corrs atomic radii of parent atom
radii of -ve ions larger than corrs atomic radii of parent atom (due to extra filled inner quantum shell)

Trend of +ve ions (Na⁺ to Si⁴⁺)
all isoelectronic w/ neon (1s²2s²2p⁶) > ~ const screening effect
increase in proton # > increase attraction > smaller ionic radius
ionic radius: Na⁺ > Mg²⁺ > Al³⁺ > Si⁴⁺

Trend of -ve ions (P^3- to Cl^-)
all isoelectronic w/ argon (1s²2s²2p⁶3s²3p⁶) > ~ const screening effect
increase in proton # > increase attraction > smaller ionic radius
ionic radius: P^3- > S^2- > Cl^-

First ionisation energy (1^st IE)

increases across period (due to increased proton # & decreased atomic radius)
-Al lower 1^st IE than Mg: single Al valence e^- in 3p orbital further from nucleus than valence e^- in 3s orbital (for Mg) > less energy needed to remove e^- (also stable 2s² config in Mg)
-S lower 1^st IE than P as increase e^- repulsion from 2 e^-s paired in sulpur's 3p orbital > more easily lost (P: no paired e^-s in 3p orbital) (also stable 3p³ config in P)
Ar: highest 1^st IE due to stable octet electronic config

Melting pt

Na, Mg, Al: metals w/ strong metallic bonds > high mp, metallic bonds: more delocalised e^-s > stronger bond (mp Al > Mg > Na)(for Al extra e^- probably not effectively used in bonding > Al mp not much greater than Mg)
Si: giant molecular structure- need to break many strong covalent bonds > v. high mp
P, S, Cl, Ar: non-metals held together by weak VDW forces > low mp (VDW forces increase w/ molecule size- P₄, S₈- large > high mp)


Electrical conductivity

Na, Mg, Al: good conductors due to delocalised e^-s (more e^-s > better conductivity)
Si: some e^-s > poor conductor
P, S, Cl, Ar: no electrons > no conductivity

Oxides of period 3 elements
Reaction of period 3 elements w/ O
sodium: -at rtp, Na oxidised on surface on exposure to air > sodium oxide layer: 4Na(s) + O₂(g) > 2Na₂O(s)
-heated in O > vigorous reaction > sodium oxide and sodium peroxide: 6Na(s) + O₂(g) > 2Na₂O(s) + Na₂O₂(s)
magnesium: -exposure to air > surface oxidation > MgO
-heated in O > Mg burns w/ bright dazzling light > white MgO(s): 2Mg(s) + O₂(g) > 2MgO(s)
[if Mg burnt in air: Mg reacts w/ N₂ > white magnesium nitride, Mg₃N₂: 3Mg(s) + N₂(g) > Mg₃N₂(s)]
aluminium: -heated in O > vigorous reaction > aluminium oxide: 4Al(s) + 3O₂(g) > 2Al₂O₃(s)
silicon: -heated in O > slow reaction > silicon(IV) oxide (silicon dioxide): Si(s) + O₂(g) > SiO₂(s)
phosphorus (white): -v. reactive: spontaneously combusts in air (oxygen) > phosphorus (III) oxide: P₄(s) + 3O₂(g) > P₄O₆(s) [w/ excess O > phosphorus(V) oxide/ P pentoxide: P₄(s) + 5O₂(g) > P₄O₁₀(s)]
[phosphorus allotropes: white & red phosphorus, white P > v.reactive > kept under H₂O > keep air away]
sulphur: -heated in O > yellow S burns w/ pale blue flame > SO₂: S(s) + O₂(g) > SO₂(g) [SO₂ + [O] > SO₃]
chlorine & argon: don't burn in O to form oxides

Reactivity w/ O: metals- Na > Mg > Al, non-metals- P > S > Si

Oxidation # of period 3 oxides

electronegativity of oxygen = 3.5, greater than that of period 3 elements > period 3 elements +ve oxidation #
across period: max oxid # increases from +1 (Na₂O) to +7 (Cl₂O₇)
metals, Na, Mg, Al, form ions > ionic bonding in oxide (electrovalency = group no)
non-metals (Si > Cl) > covalent bonding in oxide (covalency = 8 - group no / group no)

Structure & bonding of period 3 oxides
across period: giant ionic > giant covalent > simple molecular structure
Change due to diff electronegativities of atoms;
-low electronegativities of metals (Na > Al): ionic oxides, e^-s given to v. electronegative O atom
-higher electronegativities of non-metals (Si > Cl): covalent oxides, combine w/ O > share e^-s

Bp & mp of period 3 oxides
Na, Mg, Al oxides: giant ionic structure > many strong ionic bonds > high bp & mp (solids at rtp)
Si oxides: giant molecular structure > many strong covalent bonds > high bp & mp (solids at rtp)
P, S, Cl oxides: simple molecular structure > weak VDW forces > low bp & mp (rtp: P₄O₁₀-solid, SO₃- liquid, Cl₂O₇- liquid)


Period 3 oxides reaction w/ water
Na₂O: vigorous reaction > NaOH > alkaline, pH 13: Na₂O(s) + H₂O(l) > 2Na⁺(aq) + 2OH^-(aq)
MgO: slightly soluble in water > Mg(OH)₂(s), Mg(OH)₂(s) slightly soluble > weakly alkaline, pH 8: MgO(s) + H₂O(l) > Mg(OH)₂(s), Mg(OH)₂(s) > Mg(OH)₂(aq) > Mg²⁺(aq) + 2OH^-(aq)
Al₂O₃ & SiO₂: not soluble in water > no reaction w/ water
P₄O₁₀, SO₃, Cl₂O₇: react w/ water > acidic sol, P: pH 2, S & Cl: pH 1
P₄O₁₀ (s) + 6H₂O(l) > 4H₃PO₄(aq)
SO₃ (l) + H₂O(l) > H₂SO₄(aq)
Cl₂O₇(l) + H₂O(l) > 2HCl₄O(aq) [Cl₂O₇ = dichlorine heptoxide, HCl₄O = chloric(VII)/ perchloric acid]

oxide	Na2O	MgO	Al2O3	SiO2	P4O10	SO3	Cl2O7
reaction w/ water	vigorous > NaOH	slow > Mg(OH)2	insoluble	insoluble	reacts > H3PO4	reacts > H2SO4	reacts > HCl4O
equations	Na2O(s) + H2O(l) > 2Na+(aq) + 2OH-(aq)	MgO(s) + H2O(l) > Mg(OH)2(s), Mg(OH)2(s) > Mg(OH)2(aq) > Mg2+(aq) + 2OH-(aq)			P4O10 (s) + 6H2O(l) > H3PO4(aq)	SO3 (l) + H2O(l) > H2SO4(aq)	Cl2O7(l) (dichlorine heptoxide) + H2O(l) > 2HCl4O(aq) [chloric(VII)/ perchloric acid]
pH of aq sol	13	8	7	7	2	1	1

Acid-base behavior of period 3 oxides
across period: basic (metals) > amphoteric (Al) > acidic oxides (non-metals)
Na₂O & MgO: basic oxides
Na₂O: reacts vigorously w/ dil acids > salt + water: Na₂O(s) + 2H⁺(aq) > Na⁺(aq) + H₂O(l)
MgO: reacts w/ acids > salt + water: MgO(s) + 2H⁺(aq) > Mg²⁺(aq) + H₂O(l)
Al₂O₃: amphoteric- reacts w/ acid & alkalis:        Al₂O₃(s) + 6H⁺(aq) > 2Al³⁺(aq) + 3H₂O(l)
        Al₂O₃(s) + 2OH^-(aq) + 3H₂O(l) > 2Al(OH)₄^-(aq) [tetrahydroxoaluminate(IV) ion]
SiO₂, P₄O₁₀, SO₃, Cl₂O₇: acidic oxides
SiO₂: reacts w/ conc alkalis > silicate ion, SiO₃^2-_, P₄O₁₀, SO₃, Cl₂O₇: react w/ alkali > salt + water
SiO₂(s) + 2OH^-(aq) > SiO₃^2-(aq) + H₂O(l)
P₄O₁₀ (s) + 12NaOH(aq) > 4Na₂PO₄(aq) + 6H₂O(l)
SO₃ (l) + 2NaOH(aq) > Na₂SO₄(aq) + H₂O
Cl₂O₇(l) + 2NaOH(aq) > 2NaClO₄ + H₂O [ClO₄^-: chlorate(VII) ion]


Period 3 chlorides
Reaction of period 3 elements w/ Cl
sodium: heated in dry Cl > v.vigorous reaction > sodium chloride: 2Na(s) + Cl₂(g) > 2NaCl(s)
magnesium: heated in dry Cl > vigorous reaction > magnesium chloride(mainly ionic w/ some covalent nature due to polarisation- Fajan's Rule): Mg(s) + Cl₂(g) > MgCl(s)
aluminium: heated in dry Cl > vigorous reaction > covalent aluminium chloride: 2Al(s) + 3Cl₂(g) > 2AlCl₃(s)
[note: 2Al(s) + 3Cl₂(g) > Al₂Cl₆(s) (dimer), AlCl₃-dimer in soild & gas state]

silicon: heated in dry Cl > slow reaction > covalent silicon tetrachloride: Si(s) + 2Cl₂(g) > SiCl₄(l)
phosphorus (white): burns spontaneously in dry Cl at rtp > phosphorus trichloride: P₄(s) + 10Cl₂(g) > 4PCl₃(l)
[w/ excess Cl > phosphorus pentachloride: P₄(s) + 10Cl₂(g) > 4PCl₅(s)]
sulphur: molten S + Cl > red sulphur dichloride & yellow disulphur dichloride: 3S(l) + 2Cl₂(g) > SCl₂(l) + S₂Cl₂(l)
argon: doesn't react w/ Cl

Reactivity w/ Cl: metals- Na > Mg > Al, non-metals- P > S > Si

Oxidation # of period 3 chlorides

electronegativity of chlorine = 3.0, greater than that of period 3 elements > period 3 elements +ve oxidation #
across period: max oxid # increases from +1 (NaCl) to +5 (PCl₅)
P: +3-PCl₃, +5-PCl₅
S: +2-SCl₂, +1-S₂Cl₂, +4-SCl₄

Structure & bonding of period 3 chlorides
across period: giant ionic > simple molecular structure (covalent)
Change due to diff electronegativities of atoms;
-low electronegativities of metals (Na & Mg): ionic chlorides, e^-s given to v. electronegative Cl atom
-higher electronegativites of non-metals (Al > S): covalent chlorides, combine w/ Cl > share e^-s

Bp & mp of period 3 chlorides
Na & Mg chlorides: giant ionic structure > many strong ionic bonds > high bp & mp (solids at rtp)
Al > S chlorides: simple molecular structure > weak VDW forces > low bp & mp (rtp: Al₂O₆, PCl₅- solid, SiCl₄, S₂Cl₂- liquid)

Period 3 chlorides reaction w/ water

chloride	NaCl	MgCl2	Al2Cl6	SiCl4	PCl5	S2Cl2
reaction w/ water	solid > dissolves (no hydrolysis)	slightly hydrolysed > weakly acidic	covalent chlorides > hydrolysed > acidic sol [due to HCl(aq)]
pH of aq sol	7	6.5	3	2	2	2

NaCl: NaCl(s) + aq > Na⁺(aq) + Cl^-(aq)
MgCl₂: slightly covalent > little hydrolysis:
  MgCl₂(s) > MgCl₂(aq) Mg²⁺(aq) + 2Cl^-(aq)
  MgCl₂(aq) + H₂O(l) > Mg(OH)Cl(aq) + H⁺(aq) + Cl^-(aq)
Al₂Cl₆:dissolve in water >v. acidic sol (due to rel small size & high charge of Al³⁺ > polarises water molecules by drawing O atoms' e^-s > H⁺ given off)
  Al₂Cl₆(s) + 12H₂O(l) > 2Al(H₂O)₆³⁺(aq) + 6Cl^-(aq), Al(H₂O)₆³⁺(aq) Al(H₂O)5OH²⁺ + H⁺(aq)


SiCl₄, PCl₅, S₂Cl₂: hydrolysed by water > acidic sol, pH ~ 2
  SiCl₄(l) + 2H₂O(l) > SiO(s) + 4H⁺(aq) + 4Cl^-(aq)
  PCl₅(s) + 4H₂O(l) > H₃PO₄(aq) + 5H⁺(aq) + 5Cl^-(aq)
  2S₂Cl₂(l) + 2H₂O(l) > 3S(s) + 4H⁺(aq) + 4Cl^-(aq) + SO₂(g)


Reaction of period 3 elements w/ water
sodium: at rtp- vigorous reaction w/ water > NaOH + H₂ gas: 2Na(s) + 2H₂O(l) > 2NaOH(aq) + H₂(g)
magnesium: doesn't react w/ cold water, heated in steam > reacts vigorously: 2Mg(s) + 2H₂O(g) >(heat)> 2Mg(OH)₂(s) + H₂(g) [Mg(OH)₂ >(heat further)> MgO]
aluminium: doesn't react w/ cold water, slow reaction at red heat w/ steam: 2Al(s) + 3H₂O(g) >(heat)> Al₂O₃(s) + 3H₂(g)
silicon: doesn't react w/ cold water, slow reaction w/ steam at red heat: Si(s) + 2H₂O(g) >(heat)> SiO₂(s) + 2H₂(g)
phosphorus & sulphur: don't react w/ water / steam
chlorine: at rtp Cl gas reacts w/ water > HCl + HClO[chloric(I) acid]: Cl₂(g) + H₂O(l) > HCl(aq) + HClO(aq)
argon: doesn't react w/ water

Reactivity w/ water: metals- Na > Mg > Al, non-metals- Cl > Si


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