Chapter 4: Group 2 Elements ⑫

(
5m ) of so 2 -

( 1 lm )
φ
我 升

,
1. Sketch Graph 2. Thermal Stability 3. Solubility →
prHhyd
• Physical Properties • Explain + Describe Describe + Explain •
σ / Nitrate / AHUE
-

• Chemical Properties • Compare Polasiny

√
Sulphate •
Oxides/Hydroxide/ carbonate
powetostortou • Sketch graph
CuSCPDT
terual
→

真ayedensity
- -

道
—

sizel

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一
心
。
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Summary of Chapter

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Summary of Chapter

C
size
对
σ

σ
-

Anion
isalmostsimla
11 mi
solubility
:
→
solubleAUnyd >
DUVEO
Dx soluble .

AHnya CAUUE

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 ᐉ¾ಬᐉኖᐗ
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Summary of Chapter

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Summary of Chapter
d block CCF )
-

仪
= formation Transition conmplex

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੩ውብውჿ
Summary of Chapter
play daily
together
silly cat
Δ4 is : D 9

(λ )

Charge density α chareire ↓

" )

( 重)

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 Study For A
੩ውብውჿ 对
Sec B: Structure
( Si αe ↑
* Ba )
)
↓ mgr
@
— —
gcu 0 ”
1. (a) Magnesium nitrate and Barium nitrate decomposes upon OO Ba ( n 3) =
α1. Explain each of the following in terms of structure and bonding.
—

heating. CGnermal stabili 打 ) ☆ scpny NOg (a) The elements of Group 2 (Be, Mg, Ca, Sr and Ba) have a constant
-

(i) Write balanced equation for the decomposition of the two oxidation state in its compound. [3] µ
gClz

Δ
nitrate [2] (b) The boiling point of magnesium chloride (1418oC) is higher than
Bech
+
MgOcs ) 4 Noaca
2 ☆ ) toa
) Mg ( Nos ) a ( s )
Ocorlent
—

that of beryllium chloride (547O)C) [4]

) Ba ( NO ) a ( s 2 → aBaocs ) + 4 NOals ) toal (c) Magnesium Carbonate undergoes thermal decomposition at a
3
)
(ii) Which nitrate decomposes at a∞
lower temperature? [1] temperature lower (353oC) than that of Barium Carbonate
No 2 is a brown gas (1430oC) [4]
MgCNO 3 ) 2

5 ↓T least

(iii) Explain your answer in (a)(ii). [3]

型 ,

Stable

Bat SCPDT
(
2
of Mg < …
-
size
t

2t 2+ Thermal stalbility of Mg ( Nos) < Answer:

Ba
-

density of Mg
2
-

Charge 2
BaCNO3) a (a)
演 )

Polaiaing power of Mgt

2 Ba
2 t
- Group 2 Element have two valence electron, ns2 [1]
-

Bazt
Distortiontowards No i on of Ug t , 5
2
- These 2 electrons need to be removed to achieve stable octet
(b) Comment on the lattice energies for each of the following pairs.
electon cloud of configuration [1]
(i) Magnesium nitrate and Barium nitrate [2] ∞
ESE
Iohbond
-

- Group 2 element will not eliminate three electrons because the

mgt NOS
Dhhat Chanedt third ionisation energy is very large. [1]

tbenacornean
α
…
X)avsBacwosa
ugcNob * )
-

— _

Notbini
—

-
-

AHiait of Mg CNO372 7 Ba ( NO3 )a

agz (b)
- MgCl2 is an ionic compound with strong ionic bonds [1]
☆
2 t 2t
-
size of Mg a Ba
after - Size of Be2+ is smaller than Mg2+ [1]
.

(ii) Sodium fluoride and Potassium chloride [2] - so Be2+ has high charge density and high polarising power. [1]
上
Na KC 1
pa
x ←
-

-
→
P 3 - This make BeCl2 as a Ionic compound with covalent character [1]
P3 PH

∴
of
AHiat
NaF 7 KC 1 (c)
kt 3 Nat - Size of Ba2+ > Mg2+
siae of Capon ;

of Avion - Charge density of Mg2+ > Ba2+

-

C 1
-

siae ; ≥ F

- Polarising power of Mg2+ > Ba2+

- Electron cloud distortion toward CO 2- of Mg2+ > Ba2+
3
- Thus thermal decomposition of MgCO3 occurs in lower
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小
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੩ውብውჿ
Sec B: Structure
Be and Al share many common chemical properties.
(a) Give four examples in which Be is similar to Al. [4]

Answer:
aidis
salt of Be and Al are,

oxide of Be and Al are ampheterio

Ald 3 Cx5tas dimev

-

both BeCla and

孙 ion
-

Be and Al able to form

complex
Cempty p) Cempty d )

Barium and Magnesium are elements of Group 2 in the Periodic

Table. ngcos
(a) Magnesium carbonate decomposes when heated. Write a
balanced equation for the reaction. SCPDT
(b) (i) Compare the relative thermal stability of magnesium
carbonate and barium carbonate Ba
Mgat
(ii) Explain your answer to b(i) above Co ⑤

Answer:
Mgo ( s ) + co α lg )
π
Mgcoscs
)

Radium, Ra, is below barium in Group 2 of the Periodic Table.

Tlermalstability Ba θ 3 (a) (i) State what happens when a piece of radium is added to cold
i b( ) ofng o
3 <

water? Write a balanced equation for the reaction. ①

siae ③ Dlat
t Ba
2 + ② Huyd ④ solubility 的

of Mg
2
( ii ) siae <
(b) Compare the solubility of radium sulphate and barium sulphate.
Ras 04 了 Bas 04 Cx ray meal
BgIt
of Mgat
-

3
charge density Ca ) ( i ) Ras ) HaOll ) → Raloula laq 3 2 lg
Baat Answer: + ) H

Polaising Power of Mgpt ,

Bax
siae of Raat 2
Bqt b
Char
t≥
32 ion of ug2
)
o
-

e loud of
pistortion lowards
, α
group AHiat xAUlaf Buhyd
down the decrease 数
-
,

sligthly
Balos ↓Ga (
tlermal stabilityofug
o < ↓ Ga
doghificanty )

dereaseBnifrcaurthlyAMlyd
3 down tlegwup Alluya
CdoPlsthhly
-
,

ofRazt < Pat

Ra 8o 4 Ba 8o 4
Solubility of
a
-

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 Study For A
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Sec B: Structure
fread
.

*
⑪
2
1 n
scpDJO
∞ ∞ odd
Ts

/stateluufe
6
… 1 s 2 s 22 p
less than 5400 c
1s 22 s 22 63 s 23 p
63 d 104 s 24p 6
p

down
thegroup Charge density d
7
polaising power
0
size t ×
tcMg
2
,
ionicradius of Al 3
,

towards
V Disfortion e doud
of Co t, Tormal
stabilityh
t
-ion
t
Profon number of ABt Mg 1357
, 3 .

- 2
7
t
ng
2
use to potect A
(a) What do you understand by anodisation of aluminium?
-

effective nalear Charge of

Al
(b) With the aid of a diagram, explain how the anodisation
process is carried out. C2 ;

resisttocorrosion 点
Acidic
/ soluble
Answer:
lysis
(a) Anodisation is an electrochemical process to increase the
thickness of the impervious layer of aluminium oxide on the
surface of aluminium Mg (03 ( )
s ≥ MgOls) + co 2 lg )

(b) 111
-

Anode = Alcs )
A T
CathodeAnodeo -

Cathode ;
grafe 1 pt

器
anode liberated at
oxygen gas
oxidize Al to AIO 3
2 HzO ( e ) Oa He
Δ
HouCaq )
-

→ + +
1
Siaexp
-

chargedensity ↓
-

↓
( g
Alls ) +
34 oalg ) → A | zO 3 ( s
p 4 pistorhoh tohards Co 32
p
-

-
) ; -

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powen
135: thermal stability h
-
。
 Study For A
੩ውብውჿ
Sec B: Structure
A1 C13
nead .

, (a) Explain why aqueous aluminium salts are acidic [6]

w

sizel All ( 3 ( s ) U2o (e ) → ) AICH2 O( λ+ 3 C5

-

+ )
caq
1

↓ Caq )
-

Ionitatoh energy Hexaaquaaluminium (世) ion

reactiuty 2t

chargeBe
)
-

of A 13 t
ifs high
-
Due to small siae and

in
aq solufion
A1
form complex ion
( Be 2t )

JC
3

l Jattu
=
Be ( H2 θ ) 42+ Caq) + H
2 ( )
o e → BeCou) 了 ' caa ) +4 30 AlCH 20) t → AlcoucH 0 ' 6
y H Caa ) ( aq ) 的

source
-
due to high charge density ,
this
of Acidity
weaken the U -
oH bond which theh
Acidic release ut ,

2
/ Al (oH ) CH 20) 5 ] lstacaa
+ ( →Alcou ; ( 20) ) H

↓
size

High charge density

-

High Polavis afpon Power

-

Highdi fortion
3
fowards anion e cloud .

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Sec C: Essay
⑩
fread
Solubility BaCNosaG
mgCNo ) O
我
3 2

Δ
④
U2 ~

-
siae of G2cation douninorease
the
gromp

eg 04 ( aq) t HNo 3Caa) - charge densitydecreases

dgCNos ) a( s) t HaSO 4 Caa
)→ S -

polaaiziag power
decreases
'

BaSo ( s ) t HNoscaa 32 electwn decreale

-

Co clouds
Ba ( No3 ) 2 ( s ) f Haso 4 laa ) → 4 ) -

disfortion fowards

white preapitate observed .

-

TMermal stability ncreales ,

µ Bas 04
b -

solubility of gso 4 7

at
-

siae of Mg < Bat

-

down the group ,

Anhyd decreasedsgnifcandly
-

whpe, AHvat decrease slBthly

when
Allhyd < BtHiat saltisTnsomble
,

2 + 2 t
BUny⑨ of Ba <
mg
-

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」
 Study For A
੩ውብውჿ
Sec C: Essay
read .

代
∅ 1. Dolomite is a mineral consisting of calcium carbonate and
magnesium carbonate and is commonly used as a raw material
0 for cement.

(i) Suggest a way to prepare a mixture of calcium carbonate and a

the water down magnesium oxide from dolomite. Explain the reasoning behind
t

) gpoy
Reactinftyfo wards
a

cationt your method. [5]

descending the
goup, sise of
(ii) State a physical property of magnesium oxide and its use
-

onizafon ↓ related to this physical property. [2]

eneyy
-

e are
casy
to be donated
to be oaidized
G elemenf easy
-

2
,

ij) B siae increasing from a Be to

Be to Ba
Charge density decreasing foom
-

Be Ba
Polaising poner dereasing from to
-

Distorfion toward Nos electron cloud

decreasing
-

from Be to Ba

Thernal stability increasing foom Be to Ba .

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Sec C: Essay
;

fread
ca 收d (
s
.

19. Beryllium carbonate is reported to be unstable under normal The major are of Aluminium is bauxite.
conditions and should only be kept in an atmosphere of carbon (a) Describe briefly the extraction of aluminium from bauxitelw
0
(b) Explain the use of aluminium in the making ofΔ airplanes.
dioxide. In your opinion, does barium carbonate must be kept in that
same way? Justify your opinion. [5]
Answer:
(a)

-
dissolves bauxite
-
↓ mpofAl

• Pure bauxite is dissolved in molten cryolite, Na3AlF6

• Cathode: Al3+ (aq) +3e  Al(s)
• Aluminium formed is in the liquid state, hence it sinks to the
bottom of the cell and is drained off from time to time
• Anode: O2- (aq)  O2(g) + 2e
• The oxygen gas liberated burns the graphite anode to oxides of
carbon
• C(s) + O2(g)  CO2(g)
• Therefore, the anode has to be replaced from time to time

(b)
light Cd density
-

resist corrosion
: couting ofoxide layer )

)
-

Soft (
aloged

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Study For A
੩ውብውჿ
Sec C: Essay

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Study For A
੩ውብውჿ
Sec C: Essay

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 Study For A
੩ውብውჿ
Sec C: Essay
u 28

Ofread
test

θ
oy aid

,
.

gp
1. Explain the decomposition of Nitrates of Group 2 Element (From rusolution of Magnesium nitrate and of Barium nitrate
1. An aqueous
和
Magnesium to Barium) [10] can be differentiated by the addition of dilute sulphuric acid.

㉙
— _

炎 pT By writing suitable ionic equations, show how the two sulphates can
5 be differentiated. Suggest one reasons why one of the sulphates is
Answer: @ soluble in water and the others is not. [11]

• The Group 2 nitrates decompose upon heating to form Answer:

Goup aoxide rogen dioxidesgas
MOCs ) NO
α Cg
)
the corresponding , and
oxygen gas
Oα ( )
g .
• Equation: MCNO3 )a ( s) → MOCs ) +
2 4 NOα ( ∞ ) t oal )

• Down the group , Size increase from

2t
2
Ca +< Bazr
mgatc Sp <

• Polarising power of
2t 对
Ba
Mgot
2t
7 Sr 7 Ca 7

• Distortion toward NO3- electron clouds of

2t

Mgat
2t
7 Sn 7 Ca 2 Ba 2 F

• Therefore, down to group the nitrates becomes more

stable

BaCNO3)2 µ (No3 )2
• In which is more stable than g
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