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Reactivity Trends Flashcards
Cards in this deck (33)
- 1Are group 2 alkaline earth metals found in their elemental state naturally?No, they are found as stable compounds
- 2Features of the group 2 alkaline earth metals- They are in the s-block
- Their most common reactions are REDOX reactions (they become oxidised as they lose their two outer electrons, forming 2+ ions (so = reducing AGENTS) - 3What is the trend in reactivity down group 2?Reactivity INCREASES down the group
- It becomes easier to lose the 2 outer shell electrons as:
- The atomic radius increases, so distance of the outer shell electrons from the nucleus increases
- The shielding increases (more inner electron shells)
- These two factors counteract and block the effects of increasing nuclear charge down the group - 4What is the trend in 1st ionisation energies down the group?They DECREASE down the group as the increasing nuclear charge is outweighed by the increasing atomic radius and increased shielding
- 5Reaction of group 2 metals and oxygen(Beryllium won't react fully, as it forms an oxide layer, allowing it to resist fully burning)
Metal (s) + O2 (g) -> Metal Oxide (s)
This is a REDOX reaction
MAGNESIUM will burn with a brilliant white light, to form magnesium oxide - 6Reaction of group 2 metals and water(Beryllium won't react with water/steam)
They will react to form an ALKALINE metal hydroxide and HYDROGEN GAS
The reactions get more vigorous down the group, as the reactivity increases
Magnesium reacts a little differently:
STEAM: Mg (s) + H2O (g) -> MgO (s) + H2 (g)
WATER: Mg (s) + 2H2O (l) -> Mg(OH)2 (s) + H2
Magnesium will react very SLOWLY with cold water, and the reaction stops as soon as magnesium hydroxide is formed - 7What is the trend in solubility of group 2 hydroxides as you go down the group?Group 2 hydroxides are not very soluble but get MORE SOLUBLE as you go down the group (so, less and less precipitate will form)
- 8Reaction of group 2 metals and dilute acidsThey produce a SALT and HYDROGEN GAS
eg. Ba (s) + H2SO4 (aq) -> BaSO4 (s) + H2 (g) - 9Reactions of group 2 metal oxides and waterThey will react with water and then release OH- ions into solution, to form alkaline SOLUTIONS of metal hydroxides
eg. MgO (s) + H2O (l) -> Mg(OH)2 (aq)
When the solution becomes saturated with OH- ions, any further metal and OH- ions will react to form a PRECIPITATE
eg. MgO (s) + 2OH- (aq) -> Mg(OH)2 (s) - 10What is the trend of alkalinity of group 2 solutions, as you go down the group?As solubility increases, ALKALINITY WILL INCREASE as more OH- ions will dissolve into solution (basic strength increases down group)
As you go down the group, the metal ions get LARGER, so the charge density INCREASES. This lowers the attraction between OH- ions and metal ions, meaning that the ions will split away more easily in solution - 11Application examples of group 2 metal hydroxides- Ca(OH)2 is used in AGRICULTURE to increase the pH of acidic soils (neutralises the acid, to form water - metal hydroxide + acid):
Ca(OH)2 (s) + 2H+ (aq) -> Ca2+ (aq) + 2H2O (l)
- Mg(OH)2 'milk of magnesia' is used as ANTACIDS to treat acid indigestion, by neutralising the HCl in the stomach:
Mg(OH)2 (s) + 2HCl (aq) -> MgCl2 (aq) + 2H2O (l) - 12What is the trend in boiling points down group 7 (17)? (group 7 = diatomic molecules)Boiling points INCREASE down the group because the molecules get BIGGER, meaning that there are MORE LONDON FORCES between molecules, increasing the energy needed to separate them
- 13What is the trend in reactivity down group 7?Reactivity DECREASES down the group, as it becomes harder to gain an extra electron, as there are fewer forces of nuclear attraction
- 14What is the trend in electronegativity down group 7?Electronegativity DECREASES down the group (increased nuclear charge outweighed by increased shielding + greater atomic radius)
- 15Are the halogens oxidising or reducing agents?They are OXIDISING AGENTS, so are themselves reduced. The oxidising power will decrease down the group, as the reactivity decreases.
Simultaneously, the reducing power of the HALIDES INCREASES down the group (it becomes easier for the halides to lose an electron, as there is less attraction from the nucleus further down the group) - 16Properties of group 7Group 7 form STABLE HALIDE SALTS
Properties:
- most reactive non-metals
- brittle and crumbly solids
- poisonous
- smelly
- occur naturally as stable halide salts (not in their diatomic elemental form) - 17Why are fluorine and astatine usually excluded?We exclude fluorine as its TOO STRONG an oxidising agent
We exclude astatine as its RADIOACTIVE and will decay rapidly - 18General colours and states of the halogensFluorine = pale yellow gas
Chlorine = yellow-green gas
Bromine = red-brown liquid
Iodine = grey solid - 19Colours of the halogen solutions in waterChlorine = green
Bromine = orange
Iodine = brown - 20Colours of the halogen solutions in cyclohexaneChlorine = green
Bromine = orange
Iodine = deep violet - 21What are halogen-halide displacement reactions?The halogen will act as the OXIDISING AGENT (oxidised the halide ion to its halogen). The original halogen itself is then REDUCED to form its halide ions.
Only a more reactive halogen will displace a less reactive halogen from its salt, and the solution will change colour (look at colours in water + cyclohexane) - the solution formed will show you what HALOGEN is present (the halide ions displaced to a halogen or the original halogen if it wasn't reactive enough to displace the other halogen from its salt) - 22What is a disproportionation reaction?A reaction where a single species is both oxidised AND reduced, in the same reaction
- 23Example of a disproportionation reaction = the reaction of chlorine and waterCl (g) + H20 (l) -> HCl (aq) + HClO (aq)
This is a reversible reaction. A low concentration of chlorine is used.
If litmus paper was present, it would first turn RED as the products are both acids, then would DECOLORISE as chloric (I) acid contains the ClO- ions, which BLEACHES - 24Advantages and disadvantages of chlorinated drinking waterADVANTAGES = kills microorganisms so can kill bacteria that may be harmful in the water
DISADVANTAGES = can be fatal to humans in large quantities, irritating in small quantities, risk of gas leaks in the chlorination process, chlorine can react with organic compounds in the water, to form CHLORINATED HYDROCARBONS (toxic to humans + carcinogen) - 25Other reactions of chlorine- When chlorine water is exposed to bright sunlight, chlorine is DECOMPOSED, and a solution of HCl remains:
2HClO -> 2HCl + O2
- Chlorine also reacts with cold, dilute, aqueous sodium hydroxide. One of the products is used in HOUSEHOLD BLEACH:
Cl2 (aq) + 2NaOH (aq) -> NaCl (aq) + NaClO (aq) + H2O (l) - 26What is quantitative analysis?This uses simple test-tube reaction observations, rather than measurements, to test for ions
Eg. look out for gas bubbles, colour changes and precipitation - 27Test for carbonates (anion)1. Add DILUTE NITRIC ACID to the carbonate, in a test tube (any nitrates formed because of the presence of other compounds will dissolve as all nitrates are soluble)
2. Look for BUBBLES OF GAS/ FIZZING (could be production of CO2 as metal carbonate + acid -> CO2 + H2O + salt)
3. Test the gas by bubbling it through limewater (Ca(OH)2)with a delivery tube. CO2 will turn limewater CLOUDY, as CaCO3 is formed, and water - 28Test for sulfates (anion)1. Add a solution containing Ba2+ ions eg. Ba(NO3)2 - nitrates dissolve, can also use BaCl2 if certain no halides present
2. BARIUM SULFATE is formed, which is insoluble in water, so will form a WHITE PRECIPITATE
Ba(NO3)2 (aq) + Na2SO4 (aq) -> BaSO4 (s) + 2NaNO3 (aq) - 29Testing for the halides (anions)Most halides are soluble in water, but silver halides are INSOLUBLE in water
1. Make halide solution
2. Acidify it with dilute nitric acid (prevents other salts precipitating as nitrates = soluble)
3. Add a few drops of silver nitrate solution
Cl = white precipitate
Br = cream precipitate
I = pale yellow precipitate
4. Conformation tests: ammonia solution is used as the halides have different solubilities in ammonia
Cl = precipitate redissolves in dilute ammonia
Br = precipitate redissolves in concentrated ammonia
I = precipitate is insoluble in ammonia - 30Testing for the ammonium ion (cation)1. Add aqueous NaOH to the ammonium ion solution
2. Warm the mixture
3. Ammonia gas is produced (no bubbles). To confirm its ammonia gas, ammonia will turn red litmus paper blue (as its alkaline)
4. If uncertain, hold a bottle of concentrated HCl over it and look for white smoke
NH4+ + OH- -> NH3 + H2O
NH3 + HCl -> NH4Cl (white smoke) - 31Sequence of tests for analysing UNKNOWN compounds1. Carbonate (sulfate/halide don't produce effervescence so no false positive)
2. Sulfate (BaCO3 also produces a white precipitate so must do carbonate first)
3. Halides (Ag2CO3 and Ag2SO4 will precipitate so do last) - 32Sequence of tests for analysing a MIXTURE of compounds1. Carbonates (if bubbles, continue adding the acid until the bubbling stops so none is carried forward into next test, nitric acid as nitrates dissolve)
2. Sulfates - use Ba(NO3)2, NOT BaCl!, filter to remove precipitate if forms
3. Halides - 33What is the trend in the temperature required for thermal decomposition down group 2?The thermal stability increases as you go down Group 2. This is because the Group 2 ion has lower charge density, and thus distorts the carbonate ion less. The less distorted the carbonate ion is, the more stable it is, and so a higher temperature is required to decompose the carbonate.
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- A level Chemistry Flashcards on Reactivity Trends Flashcards, created by Rhea Sekhon on 28/11/2021.
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