topic 4 - inorganic chemistry and the periodic table Flashcards
what’s the ionization energy trend for group 2
- ionization energy decreases down the group
- each element going down has an extra electron shell
- more shielding
- valence electrons further from the nucleus which reduces the electrostatic force of attraction
increased positive charge ( extra protons ) is overridden by the effect of shielding - making it easier to remove outer electrons
- hence why reactivity increases going down the group
what is produced when group 2 elements react with water
metal hydroxide + hydrogen
what is produced when a group 2 metal is burnt in oxygen
solid white oxides
what happens when a group 2 metal reacts with chlorine
solid white chlorides
what is the reactivity of group 2 metals with water and what are the exceptions
- metals react readily with water to form metal hydroxides , which dissolve
- the hydroxide ions, OH- make these solutions strongly alkaline
- beryllium oxide is an exception because it doesn’t react with water and berillyium hydroxide is insoluble
- magnesium oxide is another exception because it only reacts slowly and hydroxide isn’t very soluble
what’s the difference between alkalis and bases
bases are insoluble in water. on the other hand, alkali produces ions when dissolving in water
what’s the trends for oxides pH going down group 2
the oxides form more strongly alkaline solutions going down the group because the hydroxides get more soluble
what does it mean that group 2 oxides and hydroxides are bases
they will neutralise dilute acids forming solutions of the corresponding salts
magnesium oxides reaction with water
MgO(s) + H2O (l) —> Mg(OH)2 (aq)
magnesium hydroxide reaction with water
Mg(OH)2(s) + H2O(l) —> Mg(OH)2(aq)
magnesium oxide reaction with dilute acid
MgO(s) + 2HCl(aq) —> MgCl2(aq) +H2O(l)
magnesium hydroxide reaction with dilute acid
Mg(OH)2(aq) + 2HCl(aq) —> MgCl2(aq) + 2H2O(l)
what does solubility trend in a group depend on and what are the trends in group 2
the compound anion
- group 2 elements that contain singly charged negative ions ( e.g. OH-) **increase ** solubility
- compound that contain doubly charged negative ions decrease in solubility down the group
what is the exception for solubility in group 2
most sulfates are soluble in water but barium sulfate is insoluble
what does sparingly soluble mean?
compounds like magnesium hydroxide that have very low solubility
what does thermal decomposition mean
thermal decomposition is when a substance breaks down ( decomposes ) when heated
- the more thermally stable a substance is, the more heat it will take to break it down
what’s a trend of thermal stability down a group ( carbonates and nitrates )
- thermal stability increases down a group
- the carbonate and nitrate ion and large negative ions ( anions ) and can be made unstable by the presence of a positively charged ion ( a cation )
- the cation polarises the anion, distorting it. the greater the distortion, the less stable the compound
- large cations cause less distortion than small cations as they have a lower charge density. so the further down the group, the larger the cations, the lower the charge density so the less distortion caused and the more stable the carbonate/nitrates compound
what does it mean to have a lower charge density
the charge on the ion is spread out over a larger area
what’s the difference in thermal stability in group 2 and group 1
group 2 compounds are less thermally stable than group 1 compounds
- the greater the charge on the cation, the greater the distortion and the less stable the carbonate/ nitrate ion becomes. group 2 cations have a +2 charge, compared to a +1 charge for group 1 cations so group 2 carbonates and nitrates are less stable than those of group 1
how do group 1 carbonates decompose and what is the exception
group 1 carbonates are thermally stable so you can’t heat them enough with a bunsen burner to make them decompose ( they do compose at higher temperatures )
- except Li2CO3 which decomposes to Li2O and CO2
how do group 1 nitrates decompose
to form nitrite and oxygen
2MNO3 (s) —> 2MNO2(s) + O2 (g)
- except LiNO3 which decomposes to form Li2O, NO2, and O2
how do group 2 carbonates decompose
to form the oxide and carbon dioxide
MCO3(s) —> MO(s) + CO2(g)
how does group 2 nitrates decompose
form the oxide, nitrogen dioxide and oxygen
2M(NO3)2 (s) —> 2MO(s) + 4NO2 (g) + O2 (g)
how to test how easily nitrates decompose
- how long it takes until a certain amount of oxygen is produced ( i.e. enough to relight a glowing splint )
- how long it takes until an amount of brown gas ( NO2 ) is produced. this needs to be down in a fume cupboard because NO2 is toxic