Group 2 Flashcards
(32 cards)
What is ionisation energy
It is the amount of energy required to remove an electron from an isolated atom or molecule
How does Ionisation energy change down group 2?
-Ionisation energy decreases down group 2
-This is because as you go down the group the number of electrons shells increase
-Meaning there is an extra inner shell that shield the outer electrons from the attraction of the nucleus
-Therefore the outer electrons are further way from the nucleus, which greatly reduces the electrostatic attraction between the nucleus and outer electrons
Explain the change in reactivity of the group 2 elements?
-As you go down the group the reactivity increases
-This is because the number of shells increases
-This will mean that there is more shielding between the nucleus and outer electrons
-Therefore the attraction between the nucleus and outer shell electrons decrease, so it is easier to lose two electrons
What do group 2 elements react with water to form?
The group 2 elects react with water to produce HYDROXIDES (metal hydroxide and hydrogen)
M(s) + 2H2O(l) → M(OH)2(aq) + H2(g)
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
What do group 2 elements react with oxygen to form?
The group 2 elements react with oxygen to produce OXIDES (solid oxides)
2M(s) + O2(g) → 2MO(s)
2Ca(s) + O2(g) → 2Ca0(s)
What do group 2 elements react with chlorine to form?
The group 2 elements react with chlorine to produce CHLORIDES (solids white chloride)
M(s) + Cl2(g) → MCL2(s)
Ca(s) + Cl2(g → CaCl2(S)
How do the oxides of the group 2 react with water?
The oxides react readily with water to from metal hydroxides, which dissolve. The hydroxide ions make the solution strongly alkaline
However Beryllium oxide is an exception- It docent react with water and Beryllium hydroxide is insoluble. As well as Magnesium oxide is another exception- it only reacts slowly and the hydroxide isn’t very soluble
Show the reaction of oxides with water
MO(s) + H2O(l) →M(OH)2(ag)
Show the reaction of oxides with dilute acid
MO(s) + 2HCl(aq) → MCl2(aq)+ H2O(l)
Show the reaction of hydroxides with water
M(OH)2(s) + H20(l) → M(OH)2(aq)
Show the reaction of hydroxides with dilute acid
M(OH)2(s) + 2HCl(aq) → MCL2(aq) + 2H20(l)
State the change in solubility of the hydroxides(OH-) down the group 2 elements
The solubility of the hyroxide’s increase down the group 2 elements
State the change in solubility of the sulfates(SO42-) down the group 2 elements
The solubility of the sulphates decrease down the group 2 elements
Explain the change in thermal stability down the group 2 carbonate/nitrate ions
-The thermal stability increases down the group
-This is because further down group 2 the cations increase in size
-As the larger the cations will result in a lower charge density, as the charge on the ion is spread out over a larger area, and this will cause less distortion.
-And so the less distortion the more stable the carbonate/nitrate compound
Are group 2 compound more or less thermally stable than group 1 compounds
The group 2 elements are less stable
-Because the greater the charge on the cation, the greater the distortion, therefore the less stable the compound becomes
-So as group 2 cations have a +2 charge, compared to the +1 charge for Group 1 cations.
-Therefore group 2 carbonates and nitrates are less stable than those of croup 1
How do group 2 carbonates decompose
The group 2 carbonates decompose to from the metal oxide and carbon dioxide
MCO3(s) → MO(s) + CO2(g)
CaCO3(s) → CaO(s) + CO2(g)
Calcium carbonate → Calcium oxide
How do group 2 nitrates decompose
Group 2 nitrates decompose to form the metal oxide, nitrogen dioxide and oxygen
2Ca(NO3)2(s) → 2CaO(s) + 4NO2 + O2(g)
Calcium nitrate → Calcium oxide + Nitrogen dioxide
Metal nitrate → Metal oxide + nitrogen dioxide + oxygen
How do group 1 nitrates decompose
Group 1 nitrates decompose to form the metal nitrate and oxygen
2KNO3(s) → 2KNO2(s) + O2(g)
Potassium nitrate → potassium nitrite + oxygen
Metal nitrate → Metal nitrite + oxygen
How can we test how easily nitrates decompose
-Can be tested by testing how long it take until a certain amount of oxygen is produced( enough to relight a glowing splint)
-Can be tested by testing how long it take until an amount of brown gas(NO2) is produced. This needs to be done in a fume cupboard as NO2 is toxic
How can we test how carbonates decompose
-Tested by testing how long it takes until a certain amount of carbon dioxide to be produce. Tests with lime water - which is a saturated solution of calcium hydroxide. This turns cloudy with the carbon dioxide
How to test for Carbon dioxide
Test by bubbling carbon dioxide through lime water. The CO2 reacts with the Lime water(which is calcium hydroxide) to form calcium carbonate which is insoluble in water and, this is the white precipitate.
What is Milk of Magnesia
Milk of magnesia is a suspension of magnesium hydroxide in water, that is used as anti digestion remedy called milk of magnesia. Hydrochloric acid is needed to digest food in the stomach, however sometimes there is too much of the acid and the person develops symptoms of indigestion. Taking the milk neutralises some of the hydrochloric acid and relieves some symptoms. It has very low solubility of magnesium hydroxide, meaning that the concentration of OH- ions in medicine is all very low and does not pose a risk to health.
Testing for sulphate ions
-You will need to add a solution containing barium ions, because any sulphate ions in the solution will react with the added barium ions to form a white precipitate of barium sulfate
-However Carbonate ions will also form a white precipitate with barium ions, so therefore you need add dilute nitric acid
Test:
-Add dilute nitric acid
-Add barium nitrate solution
-White precipitate forms if sulphate ions are present
Equation of the reaction is in a solution of sodium sulfate:
-Ba(NO3)2 + Na2SO4(aq) → BaSO4(s) + 2NaNO3(aq)
Ba2+(aq) + SO42-(aq) → BaSO4(s)
Why do the group 2 nitrates not melt, instead decompose
The larger more complex nitrate ion can change into smaller, more stable nitrate ion or oxide ion by decomposing and releasing oxygen gas and/or nitrogen dioxide gas
The stabilities of the nitrate and carbonate anions are influenced by the charge and size of the cation present - smaller and more highly charge cations affect these anions more
