22-Properties Period 3 Oxides and Reactions Chlorides With Water

Period 3 oxides and chlorides @e%ap of pre"ious +nowledge -

Explain the variation in frst ionisation energy across period 3 rom let to right.

Explain the reactions o period 3 elements with oxygen and chlorine Ex lain the react reactions ions o o sodium sodium and ma ma nesium nesium with with water water..

Some properties of period 3 oxides Some properties of period 3 oxides are summarised on the table below. Oxide  Na2O MgO Al2O3 SiO2 Relative melting point high high "er# high "er# high none Electrical conductivity in molten state good good good

P4O1 low none

SO2! SO3 low none

$he ele%tronegati"it# of ox#gen is 3.&. $he greater the differen%e in the ele%tronegati"it# of a period 3 elements and ox#gen! the more basi% its oxide. $he smaller the differen%e in the ele%tronegati"it# of a  period 3 elements and ox#gen! ox#gen! the more a%idi% its oxide. $he table below gi"es ele%tronegati"e "alues of period 3 elements. Element  Na Mg Al Si P S 'l Ar  Electronegativity .( 1.2 1.& 1.) 2.1 2.& 3. * $he fa%t that Al 2O3 rea%t with a%id and al+aline solutions is an e"iden%e that bonding in Al 2O3 is not  purel# ioni% or purel# %o"alent. %o"alent. ,onding in Al 2O3 is ioni% with a degree of %o"alent %hara%ter.

 Reactions of period 3 chlorides with water 

Exercise 'he%+*up 8 page 171

$he wa# in whi%h %hlorides rea%t with water depends on the t#pe of bonding present in the %hlorideoni% %hlorides do not rea%t but simple dissol"e in water to gi"e neutral solutions Na'l/s0  a  Na/a0  'l/a0 p5 6 7 2  Mg'l2/s0  a  Mg /a0  2'l /a0 p5 6 7  2 $hus Na  and Mg  ions are simpl# said to be h#drated in solution. 5#dration o%%urs be%ause of the attra%tion between the ions and the polar water mole%ules. Aluminium %hloride rea%ts with water to gi"e h#drated aluminium ions and %hloride ions. $he h#drated aluminium ions h#drol#ses b# undergoing deprotonation to form an a%idi% solutionAl'l3/s0  852O/l0  9Al/52O08:3/a0  3'l/a0. 9Al/52O08:3/a0  9Al/52O0&/O50:2/a0  5/a0 p5 6 3 $he other %o"alent %hlorides rea%t /h#drol#se0 readil# in the presen%e of water at room temperature to form the oxide or h #droxide and 5'l/g0. $he 5'l is formed as white mist# fumes! and the obser"ation of these fumes is a good indi%ation that the %hloride is %o"alent. Si'l4/l0   252O/l0  SiO2/s0  45'l/g0 p5 6 1 ; 2 Exercise 'he%+*up 7 page 173 P'l3/l0 352O/l0  53PO3/a0  35'l /a0 p5 6 1 ; 2 P'l&/s0  452O/l0  53PO4/a0  &5'l/g0 p5 6 1 * 2 'o"alent %hlorides thus rea%t with water to gi"e a%idi% solutions. $he a%idit# is due to dissol"ed 5'l.  Physical properties properties of group II elements
Their oxides and hydroxides hydroxides slightly dissolve in water to form alkaline solutions They are very abundant in the earth crust 

All group  elements ha"e an outer ele%troni% %onfiguration of ns2. $his shows that group  elements fall in the s*blo%+ of the Periodi% $able and ea%h has two ele%trons in the outer shell. =ariation of most  ph#si%al properties properties down group  is either either due to in%rease in number number of ele%tron o%%up#ing o%%up#ing shell or in%rease in mass.  Definition- An s-block element is an element whose last electron fills the s-subshell . s-subshell . /i0  Atomic size$he atomi% si>e here is metalli% radius sin%e all group  elements are metals. Atomi% si>e /metalli% radius0 in%reases down group . $his is be%ause the number of ele%tron o%%up#ing shells in%reases down the group. /ii0 /ii0 =ariatio riation n in melti melting ng point point /Mpt0! /Mpt0! densit densit# #! meta metalli lli%% radi radius us /r m0 first and se%ond ionisation energies /.?0 down group  is shown on the table below.

Element

Symbol

,er#llium Magnesium 'al%ium Strontium ,arium

,e Mg 'a Sr ,a

rm!n m .122 .18 .1(7 .21& .217

"tomic number 4 12 2 3) &8

#ass

#pt!

%$(. 24.3 4.1 )7.8 137

12) 8& )3) 78) 714

&ensity! gcm-3 1.)& 1.74 1.&& 2.8 3.&

'st ()E

2nd ()E

( 738 &( &4) &2

178 14& 11& 18 (88

Exercise 'he%+*u 1 a e 177

 Reactions of group II elements
$he table below gi"es a summar# of obser"ations made when a al+ali metal is burned in ox#gen or air. Element Observation *hen it reacts *ith oxygen E+uation for the reaction or air ,er#llium /,e0 -  No obser"able %hange ,e /s0  O2/g0   No rxn - Chite solid formed Magnesium 2Mg/s0  O2/g0    2MgO/s0. - ,right white flame if burnt /Mg0 - 5eat is released - Chite solid formed 'al%ium /'a0 2'a/s0  O2/g0    2'aO/s0. - ,ri%+ red flame if burnt - 5eat is released - Chite solid formed Strontium /Sr0 - S%arletDred flame if burnt 2Sr /s0  O2/g0   2SrO/s0. - 5eat is released - Chite solid formed ,arium /,a0 2,a/s0  O2/g0    2,aO/s0. - Apple*green flame if burnt - 5eat is released f water drips onto the surfa%e of a lump of %al%ium oxide /'aO0! a "igorous rea%tion o%%urs releasing a lot of heat released that e"en boils some of the water off. Solid %al%ium h#droxide /'a/O50 2/s00 is formed. Exercise 'he%+*u 2 a e 1) 'aO/s0  52O/l0  'a/O502/s0. n the presen%e of ex%ess water the 'a/O50 2/s0 dissol"es to form an al+aline solution with a p5 of about 11 sin%e group  oxides and h#droxides are not "er# soluble in water. 'a/O502/s0   a  'a/O50 2/a0. $he ioni% euation for the rea%tion of oxides of group  elements with water is shown below. O2*/s0  52O/l0   2O5*/a0. $he flame %olours of some group  elements %an be used to ualitati"el# identif# them.

Element

,lame colour

'al%ium /'a0 ,ri%+ red Strontium /Sr0 S%arletDred 'al%ium /'a0 Apple*green Man# metals e.g. Al! Ee! burn with a white flame. $hus flame %olour of magnesium %annot be used to identif# it.