8/3/2019 H2 Chem Summary of Group II

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Summary of Periodic Table Group II

Properties of Group II Element

Group II element Be Mg Ca Sr

Atomic No. 4 12 20 38

Atomic Radius Down the group

Nuclear charge increases.

Significant increase in screening effectoutweighsincrease in nuclear char

Effective nuclear chargedecreases down the group

Weaker electrostatic attraction between nucleus and valence electrons

Valence electrons are further away from the nucleus

Smalleramount of energy needed to remove the valence electron (for1st IE o

1st I.E.

Melting Point Group II metals have giant metallic lattice structure

Down a group, atomic radius increases

Weaker electrostatic attraction between the cations and sea of delocalised e Metallic bond strength decreases

ChemicalReactivity

Gp II metals arevery goodreducing agents

Reducing power & chemical reactivity increases down the group

Down the group,

the atomic radius increases

it becomes easier to lose the 2 outermost electrons (oxidation more likely to(OR the ionisation energy decreases thus valence electrons are more eas

E

is negative and decreasesM2+ + 2e M E < 0

e.g Mg2+ + 2e Mg E = -2.38VCa2+ + 2e Ca E = -2.87V

Reactivity of Group II elements increases. (e.g. Ca is more reactive than Mg

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Group II element Be Mg Ca Sr

Reaction withwater

No reaction withcold water orsteam

Reacts veryslightly with coldwater

It reacts rapidlywith steam to form

oxide

MgO dissolvespartially in water togive a weaklyalkaline solution

Mg(s) + H2O(g)MgO(s) + H2(g)

MgO(s) + H2O(l)Mg(OH)2(aq)

Reacts vigorouslywith cold watertogive sparinglysoluble Ca(OH)2

Ca(s) + 2H2O(l)Ca(OH)2(s) + H2(g)

Reacts

vigorou

cold wa

give sp

soluble

Sr(s) + 2H2OSr(OH)2(s)+ H

Reaction withOxygen

All Group II metals burn with a bright flame to form basic oxides. (exceptio

2Ca(s) + O2(g) 2CaO(s)2Sr(s) + O2(g) 2SrO(s)2Ba(s) + O2(g) 2BaO(s)

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Reaction of Group II Metal Oxides with Water

Group II Oxides BeO MgO CaO Sr

Nature of oxide

Amphoteric (ionic bond withcovalent character since Be

2+has

high charge density)

(reacts with both acids and bases)

BeO + 2HCl BeCl2 + H2OBeO + 2OH

-H2O Be(OH)4

2-

Basic (ionic bond)(reacts with acids to give salt a

MO + 2HCl MCl2 + H2OM = Gp II metals

Reaction withwater

Insoluble in water Slightly solublein water(pH9)

MgO + H2OMg(OH)2

Dissolve in water to give an alka

CaO(s) + H2O(l) Ca(OH)2(aq)SrO(s) + H2O(l) Sr(OH)2(aq)BaO(s) + H2O(l) Ba(OH)2(aq)

Thermal Stability of Carbonates, Nitrates and Hydroxides

Thermal stability of Group II salts increases down the grouporThermal decomposition temperature of Group II salts increases down the group

Down the group,

size of cation increases (while charge remains unchanged)

charge density of the cation decreases

polarising power of the cation decreases

cation is less able to distort electron cloud of an anion

thermal stability of compound increases.

M(NO3)2(s) MO(s) + 2NO2(g) + O2(g) where M refers to any Group II metal(brown gas)

MCO3(s)MO(s) + CO2 (g)M(OH)2(s) MO(s) + H2O(g)

MgO is used as refractory lining for high temperature furnaces because of its high melting point.CaO (quicklime) or CaCO3 (limestone) is used forliming (increased soil pH).

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