Unit 2- Periodic table group 2 and 7 Flashcards
Recall the trend in ionisation energies for group 2
2.7.1.a
- Ionisation energy decreases down group 2
- More electrons as you go down group 2
- However the attraction between the nucleus and the electrons decrease due to a greater distance and more shielding
Recall the reaction for the group 2 atoms with oxygen
2.7.1.b
- Burns in oxygen
- Forms ionic oxide
- Has a general formula of MO where M is a group 2 atom
Recall the reaction of group 2 atom with water
2.7.1.b
- Group 2 atoms react with water
- Mg reacts slowly in cold water but rapidly with steam on heating
- Mg + H2O –> MgO + H2
- Calcium reacts with cold water to produce hydrogen calcium oxide (white precipitate)
- Ca + H2O –> CaO + H2
- Barium in water also
Recall the reaction for group 2 elements with chlorine
2.7.1.b
- All group 2 react with chlorine
- Forms white chlorides
- General formula of MCl2 where M is a group 2 element
- Mg + Cl2 –> MgCl2
Recall the reactions with group 2 oxides and water
2.7.1.c
- Reacts with water
- slightly soluble
- forms the hydroxide M(OH)2 where M is a group 2 element
- Calcium oxide reacts vigorously with water
Recall the reaction between group 2 oxides with acids
2.7.1.c
- Reacts with acids to form salts
- e.g. CaO + 2NHO3 –> Ca(NO3)2
Recall the reaction between group 2 hydroxides and dilute acid
2.7.1.c
- Reacts with acids
- forms the group 2 element ion and water
- e.g. Mg(OH)2 + 2H+ –> Mg2+ + H2O
Recall the trend in solubility of group 2 hydroxides and sulfates
2.7.1.d
- Hydroxides solubility increases down group 2
- Sulfates solbulity decreases down group 2
Recall the trends in thermal stability for group 1 and 2 nitrates and carbonates
2.7.1.e
- thermal stability increases down the group for group 1 and 2
- group 1 more stable in comparison to group 2
Why are group 1 and 2 more thermically stable going down the group?
2.7.1.e
- Depend on the polarising power of the cation
- The greater the charge and smaller the ion, the greater the polarising power
- The more polarising, the less stable
- Therefore group 1 is more stable in comparison to group 2 due to haveing a +1 charge compared to +2
- Increases down the group as the molecules get larger therefore less polarising
What do nitrates for group 1 and 2 produce when decomposed?
- Group 1 produces a metal nitrite and oxygen
- 2NaNO3 –> 2NaNO2 + O2
- Group 2 produces nitrogen dioxide, oxygen and a metal oxide which includes lithium
- Mg(NO3)2–> 2NO2 + 0.5O2 + MgO
what do group 2 carbonates decompose into?
- Forms a metal oxide and carbon dioxide
- CaCO3 –> CaO + CO2
What are the metals and their corrosponding colour? 2.7.1.f
- Potassium-lilac
- Strontium-carmine/bright red
- Lithium- Crimson red
- Sodium- Yellow
- Barium- Apple/pale green
- Calcium- Brick red
- Magnesium-No colour
How are the flame colours produced for the group 1 and 2 elements?
- Upon heating, the electrons become excited
- When they go back to their normal state, the electrons emit a characteristic wavelength
Explain the characteristics of the halogen atoms
2.7.2.a
- Low boiling and melting temperature
- Solubility decreases down the group
- More soluble in hydrocarbons than water
- Fluorine is a yellow gas
- chlorine is a green gas
- Bromine is a red liquid
- Iodine is a black solid
- Oxiding power decreases down the group therefore less reactive down the group
Why does the oxiding power of the halogens decrease down the group
2.7.2.a
- As you go down group 7, the elements get larger
- More screening
- Therefore a greater electron affinity
How does the reducing power change of a halide as you decrease down group 7?
- Increases
How to test for halides?
- Add nitric acid to acidify the solution
- Added to remove impurities
- Add silver nitrate
- Silver halide precipitates form
- Add ammonia for a further test and reaction
What are the results when silver nitrate is added to the halogens?
- Fluorine - no reaction
- Chloride- white
- Bromide- pale cream
- Iodide- pale yellow
What are the results when ammonia is added to the silver halide precipitates?
- No precipitate for fluorine as soluble
- AgCl- dissolves to form a colourless solution
- AgBr- Dissolves only with concentrated ammonia to form a colourless solution
- AgI- Insoluble in any concentration
How do hydrogen halides react with in water?
- Fully ionises
- e.g. HCl + H2O -> Cl- + H3O+
How do hydrogen halides react in ammonia?
- produces a white smoke of an ammonium salt
- e.g. HCl + NH3 -> NH4Cl
What is the reaction for chlorine with cold sodium hydroxide?
- 2NaOH + Cl2 –> NaCl + NaClO + H2O
- NaClO is sodium chlorate
What is the reaction between Chlorine and hot sodium hydroxide?
- 6NaOH + 3Cl2 –> 5NaCl + NaClO3 + 3H2O
- NaClO3 is sodium chlorate (V)
What is the reaction between Iron and halogens?
- Cold fluorine with cold iron wool to oxidise iron into Iron(III) fluoride
- Chlorine gas passed over hot iron to form iron(III) chloride
- Bromine vapour passed over hot iron to form Iron(III) bromide
- Iron is oxidised from an oxidation number of 0 to +3
- Iodine vapour and hot iron react to form iron(II) iodide
What are the reactions for Iron (II) with halogens?
- Bromine and chloride oxidise iron(II) to iron(III)
- Iodine cannot
- Iron (II) oxidises iodine into iodide
- Iron (II) is green while Iron (III) is pale green
What is the reaction for halogens with concentrated sulfuric acid?
- Must be added to a solid sample
- F- forms steamy acid fumes of HF
- Cl- forms steamy acid fumes of HCl
- Br- forms steamy acid fumes of HBr which is contaminated with brown bromine vapour
- I- forms some steamy fumes of HI but mostly purple iodine vapour
