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Physical properties
The arrangement of the periodic table is
such that trends can be analsed both
across a period and down a group!
Group 2of the periodic table is shown
here! Trends that can be analseddown the group include atomic
radius" first ionization energyand
melting point!
#lements in the same group also
undergo similar chemical reactions!
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Trend in atomic radius
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Explaining the trend in atomic radius
The atomic radius of the
elements increasesdown
group 2 from berllium to barium!
The increase in radius is due to higherprinciple energ
le%els being filled" whose orbitals are located furtherfrom
the nucleus!
ElementAtomic
radius(nm)
berllium
magnesium
calcium
strontium
barium
0!112
0!14$
0!194
0!219
0!2$3
The number of protons
increases down the group&
howe%er" so does the numberof shielding electrons! #ffecti%e
nuclear charge therefore
remains appro'imatel
constant!
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First ionization energies in group 2
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Trend in melting points
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Explaining the trend in melting points
The melting points of the
elements decrease down
group 2" with the e'ception
of magnesium to calcium! berllium
magnesium
calcium
strontium
barium
ElementMelting
point ()1$(0
923
111$
10$0
1000
+ metal,s melting point depends
on the strength of its metallicbonds! This decreases down the
group because the atomic radius
increases" resulting in a weaker
attraction between the nucleus
and delocali-ed electrons!
The melting point of magnesium is lower than e'pected due
to %ariation in how its atoms pack in the metallic crstal!
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Physical properties summary
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First ionization energy of group 2 metals
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!olu"ilities of group 2 hydroxides
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!olu"ilities of group 2 hydroxides
The solubilit of the
group 2 hdro'ides
increasesdown the
group! .agnesium
hdro'ide is considered
to be sparingl soluble
and the hdro'ides ofthe lower members of
the groups are all
considered to be soluble!
+s the solubilit of the group 2 hdro'ides increases" sodoes the p/ of the solutions formed! This is because the
more of the hdro'ide that dissol%es" the greater the
concentration of hdro'ide ions / in the solution formed!
.g/2
a/2
5r/2
Ba/2
Group 2
hydroxide !olu"ility
sparingl soluble
slightl soluble
soluble
soluble
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Applications of group 2 hydroxides
+ suspension of magnesium hdro'ide is commonl called
milk of magnesia! 6t is used in medicine as a la'ati%e and to
relie%e acid indigestion!
alcium hdro'ide" alsocalled sla#ed lime" is
used in agriculture to raise
the p/ of soils! 5oil p/ is
an important factor inagriculture!
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!olu"ilities of group 2 sulfates
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!olu"ilities of group 2 sulfates
The solubilit of the group 2 sulfates decreasesdown the
group! .agnesium and calcium sulfate are considered to
be soluble" whereas strontium and barium sulfate are
considered to be insoluble!
.g54
a54
5r54
Ba54
Group 2
hydroxide !olu"ility
soluble
slightl soluble
insoluble
insoluble
7ote that this
decrease in solubilit
down the group is
the opposite of the
trend for the
solubilit of thegroup 2 hdro'ides!
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Testing for sulfate ions
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Applications of group 2 sulfates
Barium sulfate is used as a
radiocontrast agent to help
take 8ra images of the
digesti%e sstem! 6t is
sometimes known as a
barium meal,!
Barium sulfate is insoluble" so
is not absorbed b the bod
when swallowed! /owe%er"
barium is a %er good absorberof 8ras and it helps to define
structures of the digesti%e
sstem to aid in diagnosis!
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Applications of group 2 compounds
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$hemical properties summary
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%eaction &ith oxygen
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Flame tests
:hen group 2 metals are burned in o'gen" coloured
flames are produced! This is due to the presence of metal
ions! Flame tests e'ploit this fact!
magnesium ' "right &hite
calcium ' "ric# redorange
strontium ' redcrimson
"arium ' pale greenyello&green
The presence of certain metal ions can be identified b
noting the characteristic flame colour that results from
burning! The colours for group 2 metal ions are;
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Explaining flame tests
:hen heated" some electrons in an atom or ion are e'cited
to higher energ le%els! :hen the fall back to their initial
le%els" energ is emitted& sometimes seen as %isible light!
#lectrons ma be e'cited b
different amounts intodifferent energ le%els and
drop back at different times!
The colour of the flame is a
combination of all theseenerg emissions!
heatlight
en
er
g
y
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Flame test colours
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% ti ith t
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%eaction &ith &ater
% d ti ith t
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%edox reaction &ith &ater
:hen group 2 metals react with water the form the metal
hdro'ide and hdrogen gas!
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Explaining the trend in reacti1ity
The reacti%it of the elements
down group 2 from berllium to
barium increases!
+lthough increased shielding
cancels the increased nuclear
charge down the group" the
increase in atomic radius resultsin a decrease in the attracti%e
force between the outer
electrons and the nucleus!
This is because it is
successi%el easierto remo%e
electrons to form the 2= ion!
Mg
$a
!r
a
% ti f id ith t
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%eaction of oxides &ith &ater
:hen group 2 metal o'ides react with water the form the
metal hdro'ide!
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3ecomposition of group 2 car"onates
:hen heated" the group 2 metal carbonates decompose
to form the metal o'ide and carbon dio'ide gas! 5plitting
compounds using heat is called thermal decomposition!
magnesium car"onate4 Mg$+5
calcium car"onate4 $a$+5
strontium car"onate4 !r$+5
"arium car"onate4 a$+5
increasingsta"ility
The group 2 carbonates become more stable to thermaldecomposition going down the group;
M$+5(s) M+(s) * $+2(g)
3 iti f 2 it t
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3ecomposition of group 2 nitrates
Thermal decomposition of group 2 metal nitrates forms
the metal o'ide" nitrogen dio'ide and o'gen!
2M(6+5)2(s) 2M+(s) * 76+2(g) * +2(g)
Like the group 2 metal carbonates" the nitrates become
more stable to thermal decomposition down the group!
magnesium nitrate4 Mg(6+5)2
calcium nitrate4 $a(6+5)
2
strontium nitrate4 !r(6+5)2
"arium nitrate4 a(6+5)2
increasing
sta"ility
E l i i th t d i th l t "ilit
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Explaining the trend in thermal sta"ility
.etal ions become larger down group 2 but ha%e the same
charge! This means their charge densityis reduced!
+ metal ion with a high
charge densit has
strong polari-ing power!
6t can therefore polari-ethe carbonate ion"
making it more likel to
split into 2 and 2
when heated! polarization
+ metal ion with a low charge densit has weak polari-ing
power" meaning the carbonate ion is less polari-ed and
therefore more thermall stable!
E0uations for reactions
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E0uations for reactions
!ta"ility of group 2 car"onates
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!ta"ility of group 2 car"onates
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Glossary
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Glossary
8hat9s the #ey&ord:
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8hat9s the #ey&ord:
Multiple choice 0uiz
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Multiplechoice 0uiz
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8hat are the halogens:
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8hat are the halogens:
The halogens are the elements in ?roup ) of the
periodic table!
The name halogen comes from the ?reek
words for saltmaking!
Physical properties of halogens
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Physical properties of halogens
Trends in "oiling point
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Trends in "oiling point
/alogen molecules increase in si-e down the group! This
leads to greater %an der :aals forces between molecules"
increasing the energ needed to separate the moleculesand therefore higher melting and boiling points!
fluorine
atomic radius ; 72 < -,-2m
"oiling point ; --=>$
iodine
atomic radius ; --? < -,-2m
"oiling point ; -=7>$
1an der
8aals forces
Trends in electronegati1ity
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Trends in electronegati1ity
#lectronegati%it of the halogens decreases down the group
due to an increase in atomic radius!
fluorine
atomic radius ; 72 < -,-2m
electronegati1ity ; 7@,
iodine
atomic radius ; --? < -,-2m
electronegati1ity ; 2@?
6ncreased nuclear charge has no significant effect because
there are more electron shells and more shielding! 6odine
atoms therefore attract electron densit in a co%alent bond
less strongl than fluorine!
Astatine
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Astatine
The name astatine comes from the ?reek word for unstable!
6t was first made artificiall in 1940" b bombarding 209Bi with
radiation! :hat do ou predict for these properties of
astatine@
+statine e'ists in nature in onl %er tinamounts! 6t is estimated that onl 30 grams of
astatine e'ist on #arth at an one time! This is
because it is radioacti1e" and its most stable
isotope 2-,At has a halflife of onl * hours!
electronegati%it!
state at room temperature
colour
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%eactions of the halogens
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%eactions of the halogens
/alogens react with metals such as sodium and iron;
The also take part in displacement reactionswith halide
ions" such as the reaction that is used to make bromine from
potassium bromide in seawater;
halogen * hydrogen hydrogen halide
The also react with nonmetals such as hdrogen;
halogen * sodium sodium halide
chlorine *potassium
"romide
potassium
chloride"romine *
%eaction &ith iron
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%eaction &ith iron
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%edox reactions of halogens
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%edox reactions of halogens
8hat is the reacti1ity of the halogens:
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8hat is the reacti1ity of the halogens:
The reactions of the halogens with iron and hdrogen show
that their reacti%it decreasesdown the group!
/ow do ou think fluorineand astatinewould react with
iron wool and hdrogen@
6ron wool burns and
glows brightl!
6ron wool has a %erslight glow!
6ron wool glows but less
brightl than with chlorine!
chlorine
"romine
iodine
.alogen %eaction &ith iron
&ool
%eaction &ith
hydrogen
#'plodes in
sunlight" reacts
slowl in the dark!
>eacts slowl on
heating with catalst!
>eacts partialland %er slowl!
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.alogen displacement reactions
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.alogen displacement reactions
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.alogen displacement reactions
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g p
/alogen displacement reactions are redoxreactions!
$l2* 2r 2$l* r2
To look at the transfer of electrons in this reaction" the
following two half eAuations can be written;
hlorine has gained electrons" so it is reducedto l ions!
:hat has been o'idi-ed and what has been reduced@
2r r2* 2e$l2* 2e
2$l
Bromide ions ha%e lost electrons" so the ha%e been
oxidizedto bromine!
+xidizing a"ility of halogens
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g y g
fluorine
increas
ingo
xidiz
inga
"ility
iodine
"romine
chlorine
6n displacement reactions between
halogens and halides" the halogen
acts as an oxidizing agent!
This means that the halogen;
:hat is the order of o'idi-ing
abilit of the halogens@
is reducedto form the halide ion!
gainselectrons
oxidizesthe halide ion to thehalogen
+xidizing a"ility of halogens
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g y g
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%eaction of chlorine &ith &ater
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hlorination of drinking water raises Auestions about indi%idual
freedom because it makes it difficult for indi%iduals to opt out!
hlorine is used to purif water supplies
because it is to'ic to bacteria" some of
which can cause disease! +dding it towater supplies is therefore beneficial for
the population!
/owe%er" chlorine is also to'ic to humans"so there are risks associated with gas leaks
during the chlorination process! There is
also a risk of the formation of chlorinated
hdrocarbons" which are also to'ic!
leach and the chlorate() ion
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( )
/ousehold bleach commonl contains the chlorate() ionB
$l+" in the form of sodium chlorate6" 7al!
$l+* .2
+ * $l* 2+.
The chlorine has been reduced because it has gained
electrons! 6ts o'idation state has decreased from =1 in
lto 1 in l!
/ow man electrons are needed to balance this eAuation@
The chlorate6 ion beha%es as an oxidizing agent! 6t o'idi-es
the organic compounds in food stains" bacteria and des!
/as the chlorine been o'idi-ed or reduced in the reaction@
2e-
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.alides
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:hen halogens react with metals" the form compounds
called halides! .an naturalloccurring halides ha%e
industrial" household and medical applications!
caesium chloride
sodium
he'afluoroaluminate
titanium6C chloride
lithium iodide
potassium bromide
.alide Formula Cses
sl
7a+l
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dentifying halide ions
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.ydrogen halides
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The hdrogen
halides are
colourless gasesat room
temperature!
/drogen fluoride has an
une'pectedl high boiling point
compared to the otherhdrogen halides! This is due to
hdrogen bonding between the
/< molecules!
.ydrogen halide oiling point (>$)
/