topic 4a: group 1 and 2 Flashcards
trend in 1st IE down group 2
- atomic radius increases down the group
- more electron shells more shielding
- further distance nucleus from outer shell e-, weaker ESA
- less energy required to lose
- outweighs effect of increased no protons
reactivity of group 2 metals down the group
- increases
- atomic radiu sincreases
- more shielding
- further distance nucleus and outer shell e-, weaker esa
- less energy required to lose
- outwewighs effect of increased no protons
group 2 metal + O2
2Mg +O2 = 2MgO
observation Mg with oxygen
bright white light
consideration of using Mg in practicals etc?
- oxidises to form a thin layer of MgO
- must be cleaned off with an abrasive before
group 2 metal + Cl2
Mg + Cl2 = MgCl2
group 2 metal and STEAM !!!!!1
Mg + H2O = MgO + H2
group 2 metal and WARM WATER
Mg + 2H2O = Mg(OH)2 + H2
water after reaction with a group 2 metal
- alkaline
- hydroxide formed
observations down the group of group 2 metals with water?
- more vigorous effervescence
- metal disappears
- exothermic (feels hotter)
- WHITE PPT FOR CALCIUM
solubliity of group 2 hydroxides down the group
hydroxides are MORE soluble down th group
hence in the reactions w water, some are white ppt
group 2 oxide + water
MgO + H2O = Mg(OH)2
which is more basic, Mg(OH)2 or Ca(OH)2?
- calcium
- more soluble
- greater dissociation in water, so higher [OH-]
group 2 hydroxiee / oxide + acid
- metal chloride
- water
is magnesium ghydroxide soluble
no
limewater reaction
Ca(OH)2 + CO2 = CaCO3 (SOLID) + H2O
solubility of sulfates down group 2
less soluble
so baso4 the least soluble
thermal decomposition
the use of heat to break down a reactant into 1+ product
decomposition of a g2 carbonate
MgCO3 = MgO + CO2
thermal stability of g2 carboantes down the group
- MORE thermally stable
- ionic radius of cation increases
- polarising power decreases
- co3 2- polarised less
- less strain (Weakening) on c-o bond
- so breaks less easily
which of the g1 carbonates decompose and why?
ONLY LITHIUM
- tiny IR
- small enough to polarise the c-o bond in co3 2- so that the bond breaks and will decompose
-
decomposition of lithium carbonate
Li2CO3 = Li2O + CO2
decomposition of magnesium nitrate
2Mg(NO3)2 = 2MgO +4NO2 + O2
observation of decomposition of group 2 nitrate
- brown gas NO2 evolving
- solid MELTS
- then white solid reforms
trend in decomposition of g2 nitrates
- same as carbonates
- mg2+ smallest IR, most polarising
- puts most strain and weakens the n-o bond the most
- most easy
decomposition of group 1 nitrate
2NaNO3 = 2NaNO2 + O2 (nitrite + oxygen_
which group 1 nitrate will decompose the same as a group 2 nitrate?
LITHIUM
4Li(NO3) = 2Li2O + 4NO2 + O2
method of flame test
- nichrome/platinum wire [inert, high mp, no colour]
- dip in conc HCl and then put in bunsen flame to clean
- insert in sample
- put in flame , and observe colour
explain why there is colour
- heat energy
- causes electron to excite move to higher energy level
- then drops back down to ground state
- energy is emitted as visible light
if a gas is produced, water level
decreases
describe exp for how to compare thermal stability of g2 NITRATES + a safety precaution
- fume cupbaord(NO2 TOXIC)
- gas syringe, time taken to produce x volume of gas
- use equal masses of nitrate, equal distance of bunsen so same strength of heating
why do diff atoms show as diff colours
- energy levels are different distances apart
- different aounts of energy emitted
why if u mix 2 cations might u not be able to find out which 2 are present in a flame test?
darker colour obscures the lighter one
why use HCl for step 2 of flame test?
forms volatile chlorides
control variables for vailidity in the thermal stability of CARBOANTES test
- same MOLES of carbonate
- same distance from BB
- same volume LW
phosphorus exists as
P4
how to improve the exp about thermal stability of carbonates
- standardise by using disappearing cross
