topic 4 - periodic table Flashcards
group two elements reaction with oxygen
rigerous reactions
need heat
get more reactive as you go down
2M(s) + O2(g) –> 2MO(s)
group two elements reaction with chlorine
more vigorous down the group
M(s) + Cl2(g)–>MCl2(s)
group two elements reaction with water
magnesium dosent react very visibly or fast
M(s) + 2H2O(l) –> M(OH)2(s) + H2(g)
magnesium in steam
magnesium reacts vigorously in steam a rapid and visible reaction
you can test the product by testing for hydrogen at the top of the tube
reaction of the oxides of water
react with water to form alkalis
form colourless solutions
MO(s) + H2O(l) –> M(OH)(aq)
trends in solubility of the hydroxides
increases down the group
milk of magnesia
magnesium hydroxide in water
indegestion remedy
neutrilises some of our stomach acid
reaction with acid group 2
neutrilisation reactions
form salts and water
eg. Mgo + H2SO4 –> MgSO4 + H2O
trends in solubility of the sulfates 2
decreases down the group
test for sulphate ions
add barium chloride or nitride solution
white precipitate will be formed
dilut nitric acid or hydrochloric acid is added
thermal stability
how stable a compound is when heated
factors affecting thermal stability
charge
ionic radius
complex ions
trend in boiling temperatures group 7
increase down the group
as london forces increase in strength
as there is an increase in number of electrons/size
so more energy needed to overcome the forces
thermal stability of nitrates
brown fumes- decomposition
nitrogen dioxie and oxygen
no brown fumes - lesser decomposition
just oxygen
all group 2 undergo decomposition
only lithium does in group 1
the rest undergo lesser decomposition
thermal stability of carbonates
group two and group one behave differently
flame test colours
lithium
sodium
potassium
calcium
barium
l- red
s- yellow
p- lilac
c- brick red
b- green
what causes flame test colours?
electrons absort energy and move ot higher energy levels from their ground state to an excited state
then when the electron moves back to its ground state it releases energy in the form of light energy and the specific frequency omits the colour
test for ammonium ions
no colour in flame test so add
sodium hydroxide solution and warm
ammonia gas is released
test - turns damp red litmus paper blue
whats the trend in electronegativity of the halogens
decreases
whats the trend in reactivity if the halogens
decreases
reaction of chlorine with water
disproportionation reaction
forms chlorine water
Cl2 + H2O –> HCl + HClO
halide ion trends
reducing power increases
2X¯ –> X2 + 2E¯
oxidising power decreases
how do you cary out a flame test
use a platnum wire
dip into concentrated hcl
dip into solid
put in roaring flame
what changes thermal stability
if atomic radius increases or charge decreases the polarisation ability decreases which is the ability to distort an atom
this means the bond is weakened less
so when the atomic radius decreases and charge increases the polarisation ability increases and the bond is weakened more making it less stable
