Group 2 and Group 7 Elements Flashcards
Group 2 elements ____ two electrons when they react
lose
What happens to the atomic radius as you go down group 2 ?
increases
What happens to the first ionisation energy as you go down group 2?
decreases
Each element down group 2 has an extra electron shell compared the the one above
The extra shell shields the outer electrons from the attraction of the nucleus and means outer electrons are further away from the nucleus
What happens to the reactivity as you go down group 2 ?
Increases as the more reactive the element the easier it is to lose electrons (linked to first ionisation)
Melting points generally ________ down group 2
Decrease
The larger the ionic radius, the further away the delocalised electrons are from the positive nuclei and the less attraction they feel. So it takes less energy to break the bonds
However magnesium has a drop as the arrangement of metallic ions changes.
show oxidation of Ca
Ca –> Ca2+ + 2e-
When group 2 metals react with water, what are the products formed?
show example Ca
products = metal hydroxide and hydrogen
Ca(s) + 2H2O(l) –> Ca(OH)2 (aq) + H2(g)
water is the oxidising agent in this reaction
Generally compounds of group 2 elements that contain singly charged negative ions (e.g. OH-) _______ in solubility whereas compounds that contain doubly charged negative ions (e.g. SO4 2- ) ________ in solubility
increase
decrease
Most sulfates are soluble in water but ______ _______ is insoluble
barium sulfate (BaSO4)
Test for sulfate ions
If acidified barium chloride (BaCl2) is added to a solution containing sulfate ions then a white precipitate of barium sulfate is formed.
Ba2+(aq) + SO4 2- (aq) –> BaSO4 (s)
e.g. BaCl2 (aq) + FeSO4 (aq) –> BaSO4 (s) + FeCl2 ( aq)
Group 2 elements are known as the alkaline earth metals and many of their common compounds are used for _________ acids.
neutralising
examples
calcium hydroxide is used in agriculture to neutralise acid soils.
magnesium hydroxide is used in some indigestion tablets as an antacid
H+(aq) + OH-(aq) –> H2O(l)
Use of barium sulfate
it is opaque to x rays so can help diagnose problems with oesophagus, stomach etc
Halogens are the highly reactive ________ of group 7
non metals
What happens to electronegativity of group 7 as you go down the group?
decreases
electrons are further from the nucleus and are shielded by more electrons
Why do the boiling points of group 7 increase as you go down the group?
increasing strength of van der Waals as the size and relative mass of molecules increases. This trend is shown in the changes in physical state from fluorine (gas) to iodine (solid)
Halogens ______ less reactive halide ions from solution
displace
Why are group 7 less oxidising as you go down the group?
When the halogens react, they gain an electron. They get less reactive down the group, because the atoms become larger. The outer shell is further from the nucleus so less strongly attracted to it.
If you mix chlorine gas with cold, dilute, aqueous sodium hydroxide you get sodium chlorate solution which is ____
give equation
What are the uses of this?
bleach
2NaOH(aq) + Cl2(g) –> NaClO(aq) + NaCl(aq) + H2O(l)
used in water treatment to bleach paper and textiles , cleaning toilet etc
When you mix chlorine with water you get chloride ions and ______ ions
chlorate
chlorate ions kill bacteria so makes water safe to drink or swim in.
Why is chlorine an important part of water treatment?
kills disease causing microorganisms
some chlorine persists in the water and prevents reinfection
prevents the growth of algae , eliminates bad smells and tastes, removes discolouration
What are the risks of using chlorine to treat water?
chlorine gas is very harmful if breathed in
liquid chlorine can cause chemical burns
water contains a variety of organic compounds ie from decomposition of plants. chlorine reacts with these compounds to form chlorinated hydrocarbons which can be carcinogenic
To reduce something, the halide ions needs to lose an electron from its outer shell. How easy this is depends on the attraction between the nucleus and the outer electrons. As you go down the group, the attraction gets _____ because:
the ions get bigger so electrons are further away from the positive nucleus
there are extra inner electron shells so there is a greater shielding effect
So the further down the group the halide ion is the easier it is to lose electrons and the _______ its reducing power.
weaker
greater
What happens when a halide reacts with concentrated sulfuric acid?
gives a hydrogen halide but what happens next is dependent on which halide
check page 106
Test for halide ions?
First add dilute nitric acid to remove ions which may interfere with the test.
Then add a few drops of silver nitrate solution ( AgNO3(aq))
A precipitate is formed (of the silver halide)
Ag+(aq) + X-(aq) –> AgX(s)
