group 2 and 7 Flashcards
trend in ionisation energy as you go down group 2
decreases
why does IE decrease down group 2
atomic radius increases
shielding increases, decreasing electrostatic attraction to the outer electron, meaning less energy is required to remove it
reactivity down group 2
increases as 1IE and 2IE decreases down the group, meaning that it’s easier to form 2+ ions
reactions of group 2 with oxygen
2M + O2» 2MO
reactions of group 2 with chlorine
M + Cl2»_space; MCl2
reactions of group 2 with water
how does this affect the pH
support w an ionic equation
increases reactivity down the group. Be doesn't react at all, Mg will react slowly w cold water while the rest down the group react more vigorously. M+2H2O >> M(OH)2 this increases the pH O2-+H2O >> 2OH-
what happens to the solubility of group 2 hydroxides as you go down the group
solubility increases down the group, increasing the pH
test for CO2
add aqueous calcium hydroxide and a white precipitate should form
Ca(OH)2 (aq) + CO2 (g)»_space; CaCO3 (s) + H2O
uses of group 2 oxides
Mg hydroxide (milk of magnesia) treats indigestion Ca(OH)2 (lime) raises the pH of soil
why is magnesium hydroxide safe for consumption?
although Mg (aq) is toxic to the human body, Mg(OH)2 is insoluble and so non-toxic.
equation for lime use in agriculture
Ca(OH)2 + HNO3»_space; Ca(NO3)2 + 2H2O
solubility of group 2 sulfates
decreases down the group
which group 2 sulfates are insoluble
Sr and Ba
use of BaSO4
used as a barium meal in x raying of soft tissue as a contrast fluid.
ordinarily toxic, Ba is insoluble as a sulfate so is safe for consumption
how to test for sulfate ions
- add dilute HCl or HNO3 (to remove CO32-)
- Add Ba(NO3)2 (source of Ba2+)
- a white ppt will form
what happens to nitrates and carbonates upon heating
they decompose
what are the 2 reactions involved in the decomposition of group 2 nitrates
metal nitrate» metal oxide + oxygen + nitrogen dioxide
metal nitrate» metal nitrite + oxygen
group 1 nitrates that decompose into nitrogen dioxide
Li ONLY
group 2 nitrates that decompose into nitrogen dioxide
ALL OF THEM
what colour is nitrogen dioxide
brown
factors affecting the decomposition of group 2 nitrates
charge
ionic radius
complexity of nitrates or carbonates
how does ionic radius and charge affect stability of group 2
larger, more complex ions of a lower charge are most stable
group 1 metals that decompose
Li ONLY
group 2 metals that decompose
ALL OF THEM
Mp/bp Trend of group 7
Why?
Increases as you go down group 7
As intermolecular forces become stronger due to larger temporary and induced dipoles (due to more electrons) meaning more energy is needed to break them.
Electronegativity Trend down group 7
Decreases
Atoms get larger down group.
Constant Z eff (=protons- shielding electrons)
F is most electronegative element
Electronegativity define
The ability of an atom to attract electron density towards itself in a covalent bond.
Trend in reactivity down Group 7
Decreases
Atomic radius increases, causing electronegativity to decrease
But I- is a better reducing agent than F-
Chlorine Reactions w group 1 and 2
2Na + Cl2»_space; 2NaCl
Mg+Cl2»_space; MgCl2
Displacement reactions of group 7
Takes place in H2O or cyclohexane
More reactive halogen will displace a less reactive one.
How do you see a more distinct colour change in displacement reactions of group 7
Add cyclohexane to see a greater change
Colours of group 7 in cyclohexane
Without cyclohexane.
Cl2 > yellow> colourless prior
Br2 > brown > yellow prior
I2 > purple > yellow prior
Disproportionate on define
The Oxidation and reduction of the same element in an equation
Uses of chlorides
Weed killer
Bleach
Disinfectant
Trend in oxidising power as you go down group 7
Decreases
Trend in reducing power as you go down group 7
Increases
3 forms sulfuric acid can be oxidised to
Sulfur dioxide SO2 (4+)
Sulfur (0)
Sulfur hydride (-2)
