8) Reactivity trends Flashcards
Describe Group 2 elements
reactive metals
do not occur in their elemental form naturally
reducing agents in redox reactions which form 2+ ions
Group 2 element + oxygen ->
metal oxide (MO)
Describe Magnesium’s reaction with oxygen
burns with a white light to form a white metal oxide
Group 2 element + water ->
alkaline hydroxide (M(OH)2) + hydrogen gas
metal + acid ->
salt + hydrogen
A group 2 element’s reaction with water becomes _ vigorous down the group as reactivity _?
more
increases
A group 2 element’s reactions with oxygen, water and acids are all examples of what type of reaction?
redox
State and explain the reactivity trend down Group 2
reactivity increases
first and second ionisation energies decrease down the group because the attraction between the nucleus and outer e- decreases as a result of increased atomic radius and shielding
Describe the reaction of group 2 oxides with water
release OH- and form alkaline solutions of the metal hydroxide
however, group 2 hydroxides are only slightly soluble in water so when the solution becomes saturated, any further metal and hydroxide ions will form a solid precipitate (M(OH)2 (s))
Solubility of group 2 hydroxides in water _ down the group, so resulting solutions contain _ OH- ions and are _
increases
more
more alkaline
How can the solubility trend of Group 2 hydroxides be shown experimentally?
add a spatula of oxide to a test tube of water
shake
you will see whether or not there is sufficient water to dissolve the hydroxide that forms
pH of solutions can be tested
What are group 2 oxides, hydroxides and carbonates all useful as?
bases
Give two uses of group 2 bases
Ca(OH)2 added to fields as lime to increase pH of acidic soils in agriculture
as antacids for treating acid indigestion in medicine - often magnesium / calcium carbonates or ‘milk of magnesia’ (suspension of white Mg(OH)2 in water) to neutralise HCl(aq) in stomach
Describe halogens
reactive non-metal elements
do not occur in their elemental form in nature (instead as stable halide ions dissolved in sea water / combined with sodium or potassium as solid deposits)
exist as diatomic molecules at RTP
as solids form lattices with simple molecular structures
Boiling point _ down the halogen group because _?
increases
more electrons
stronger London forces
more energy required to break intermolecular forces
What do displacement reactions of halogens show?
reactivity of halogens decreases down the group
Why does reactivity of halogens _ down the group?
decrease
increased atomic radius and shielding
decreased nuclear attraction
Describe the displacement reactions of halogens
a solution of each halogen is added to aqueous solutions of the other halides
if the halogen is more reactive than the halide present:
- halogen displaces halide from solution
- solution changes colour
