Module 3 - [ch8] (reactivity trends) Flashcards
what are the group 2 elements also known as
alkaline earth metals
what is the most common reaction of group2 elements
redox
loses its two outermost electrons and be reduced
acts as a reducing agent
group2 metal + oxygen
metal oxide
group2 metal + water
alkaline hydroxide + hydrogen
M(OH)2 + H2
how does reactivity of the group2 metals change going down the group
becomes more vigorous down the group
reactivity increases down the group
metal + acid
salt + hydrogen
why does reactivity increase down group 2
the atoms of group2 lose 2 electrons to form 2+ ions
ionisation energy decreases down the group
due to increases atomic radius, electron shielding
less energy needed for reaction to occur down the group
group2 oxide + water
release hydroxide ions (OH~)
only slightly soluble in water
when solution becomes saturated
Ca+(aq) + OH~(aq) -> Ca(OH)2(s)
solid precipitate formed
solubility of hydroxides in water
increases down the group
down group contain more OH~ (aq) ions and are more alkaline, pH increases
what are group 2 compounds often used as
bases
oxides
hydroxides
carbonates
group2 compound uses
Ca(OH)2
calcium hydroxide
agriculture - added to fields as lime to increase pH of acidic soils
neutralises acidic soil forming neutral water
Mg(OH)2
magnesium hydroxide
antacids to treat acid indigestion
CaCO3
calcium carbonate
+ HCl (stomach acid)
equation for antacid
CaCO3(s) + HCl(aq) -> CaCl(aq) + H2O(l) + C2O(g)
OR
Mg(OH)2(s) + 2HCl(aq) -> MgCl2(aq) + 2H2O(l)
trend in boiling points of halogens
increases down group
more electrons
stronger london forces
more energy required to break intermolecular forces
how do halogens exist
as diatomic molecules
most common type of reaction for halogens and why
redox
each halogen atom has 7 electrons on outer shell
only needs to gain one for stable noble gas configuration
each halogen atom reduced to form 1- halide ion
acts as an oxidising agent
what experiment can be carried to show how the reactivity of halogens decrease down a group
displacement reaction
oxidation
if the halogen is more reactive it displaces the halide in solution
colour change
Cl2(aq) Br2(aq) I2(aq) Cl~ X none none Br~ orange X none I~ purple purple X
how can you tell apart Cl2, Br2 and I2
solution in water
Cl2 - pale green
Br2 - orange
I2 - brown
not very clear, hard to distinguish between orange and brown
+ organic non-polar solvent
cyclohexane
shake
non-polar halogens dissolve more readily in non-polar solvent
Cl2 - pale green
Br2 - orange
I2 - violet
fluorine
pale yellow gas
extremely reactive
astatine
extremely rare
radioactive and decays rapidly
never been seen
predicted to be the least reactive halogen
reactivity of halogens
reactivity decreases down group
atomic radius increases
shielding increases
nuclear attraction decreases
more difficult to attract electron to outer shell
what is disproportionation
redox reaction in which the same element is oxidised and reduced
what is chlorine used in
water purification
chloric acid produced (HClO) kills bacteria
chloric acid(I) acid also acts as weak bleach
what type of reaction is chlorine and water
give the equation
disproportionation
Cl2(aq) + H2O(l) -> HClO(aq) + HCl(aq)
household beach
what is the equation
NaClO
Cl2(aq) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) H2O(l)
disproportionation
reaction between chlorine and water is limited by low solubility of chlorine in water
if water has sodium hydroxide much more chlorine dissolves
