Group 1 and 2 Flashcards
What can all group 2 metals form
ionic compounds in which they donate these two outermost electrons
are group 2 metals reducing agents or oxidising agents
act as reducing agents) to become an ion with +2 charge (so they themselves become oxidised)
What is first ionisation energy
energy needed to remove the first outer electron of an atom
how is the increased nuclear charge down the group outweighed
increased shielding effect and a larger distance between the outermost electrons and nucleus outweigh the attraction of the higher nuclear charge
when reacting group 2 metal with water and oxygen what is the general equation
2M (s) + O2 (g) → 2MO (s)
M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g)
what are the exceptions when reacting group 2 metal with water and oxygen
Sr and Ba also form a peroxide, MO2
Be which does not react with water
why is the reaction of magnesium with cold water form a weak alkaline
magnesium hydroxide is only slightly soluble
what happens when magnesium is heated in steam
it reacts vigorously with steam to make
Mg (s) + H2O (g) → MgO (s) + H2 (g)
all group 2 oxides are basic except which one
BeO which is amphoteric (it can act both as an acid and base)
what happens when group 2 metal oxide reacts with water
oxide + water → hydroxide2
Group 2 oxides react water to form alkaline solutions which get more alkaline going down the group
what happens when group 2 oxide with hcl / sulfuric acid
Group 2 sulfates or chlorides with water
insoluble sulfates form at the surface of the oxide, which means that the solid oxide beneath it can’t react with the acid
what do group 2 metal hydroxides form when react with dilute acid
colourless solutions of metal salts
The sulfates decrease in solubility going down the group
group 2 hydroxide + dilute hydrochloric acid → magnesium chloride + water
Explain the solubility if group 2 hydroxides
Going down the group, the solutions formed from the reaction of Group 2 oxides with water become more alkaline
The higher the concentration of OH- ions formed, the more alkaline the solution
The alkalinity of the formed solution can therefore be explained by the solubility
how do oxides and hydroxides dissolve in water show ionic equations
O2- (aq) + H2O(l) → 2OH- (aq)
X(OH)2 (aq) → X(aq) + 2OH- (aq)
what happens when group 2 carbonate gets decomposed
they are heated to form the metal oxide and give off carbon dioxide gas
Going down the group, more heat is needed to break down the carbonates
which group 1 nitrate gets thermally decomposed and what happens to rest of group 1 nitrates
4LiNO3 (s) –> 2Li2O (s) + 4NO2 (g) + O2 (g)
2XNO3 (s) —> 2XNO2 (s) + O2 (g)
why does the thermal stability of group 1 and group 2 increase down group
more heat is needed to break down the carbonate and nitrate ions
The smaller positive ions at the top of the groups will polarise the anions more than the larger ions at the bottom of the group
The small positive ion attracts the delocalised electrons in the carbonate ion towards itself
The higher the charge and the smaller the ion the higher the polarising power
The more polarised they are, the more likely they are to thermally decompose as the bonds in the carbonate and nitrate ions become weaker
how can you carry out a flame test
any mention of platinum / nichrome wire /
loop
(1)
dip the wire into (clean / fresh concentrated) hydrochloric acid / HCI
(1)
dip the (wet) wire into the solid and place in a (non-luminous
/ roaring / blue Bunsen) flame
why does the flame colour occur
heat causes the electron to move to a higher energy level
The electron is unstable at this energy level so falls back down
As it drops back down from the higher to a lower energy level, energy is emitted in the form of visible light energy with the wavelength of the observed light
why does mg2+ not have a colour
The energy emitted during a flame test involving magnesium is outside the visible spectrum
no emission of light
why add a small amount of sulphuric acid in carbonate ion test
The acid reacts with the carbonate ions to form carbon dioxide and water, and so gets rid of them before you add the barium chloride.
does magnesium carbonate have higher thermal stability than barium and why
(Magnesium carbonate is less thermally stable because) Mg2+ is smaller has a greater charge density
Polarising power
*so more likely to polarise / distort (the carbonate (ion) / anion)
Bonds
* and so weaken the C-O bond or the bond(s) within the carbonate ion
reaction of carbonate with acid
salt + water + carbon dioxide
two reasons why wire is made of nichrome and not iron
iron produces a colour nichrome produces no colour (when heated in the flame test)
iron can produce a colour/sparks
(1)
nichrome is inert/ stable to heat/unreactive or
iron reacts with oxygen/air and or hydrochloric acid
why is acid dipped into wire and heated
to clean the wire and remove any residue/ impurities
two observations when magnesium nitrate is heated
brown fumes of no2 gas
white powdered solid forms
explain trend in thermal stability in group 2 nitrates
Nitrates increase in stability down Group 2 as ionic
radius increases (as you go down group)
* so polarising ability of metal (ion) decreases / distorts (the electron cloud of) the anion less
*weakening of N-O bonds (in nitrate ion) is less
two gases given off in thermal decomposition of group 2 nitrate and appearances
oxygen - relights
nitrogen dioxide - brown fumes
X(NO3)2 –> XO + 1/2O2 + 2NO2
what does the thermal decomposition of a G2 carbonate form
metal oxide and carbon dioxide
flame colour for Li+
red
flame colour for Na+
yellow
flame colour for K+
lilac
flame colour for Rb+
red
flame colour for Cs+
blue
flame colour for Mg2+
Nothing
flame colour for Ca2+
brick red
flame colour for Sr2+
red
flame colour for Ba2+
green
explain how reactivity of group 2 elements is determined by electronic configuration
the outerfurther from the nucleus
there is more shielding (from shells of inner electrons) or
there is an increase in repulsion between the filled inner shells and the electron removed
so the (first) ionisation energy decreases (down the group) and
so the reactivity increases
why experimental may differ from calculated
incomplete reaction
test for sulfate ions
add a few drops of dilute hydrochloric to the sample.
add a few drops of dilute barium chloride or barium nitrate solution.
a white precipitate
give a reason why a flame test on mixture of potassium chloride and strontium chloride
red will mask lighter colour
give reason why the wire is dipped into acid and heated in first stage
remove residue / clean wire
why is fresh concentrated HCL used in second stage
HCL contaminated with residue from previous test
test for ammonia
adding sodium hydroxide solution and warming gently. If the compound contains ammonium ions, you will get ammonia gas produced which you can test with damp red litmus paper which it turns blue
Thermal decomposition of group 2 carbonates and lithium carbonate (rest of group 1 carbonates don’t decompose)
XCO3 (s) —> XO (s) + CO2 (g)
