Periodicity Flashcards
Trend for first ionisation energies for Period 3 elements
- increases across period due to increasing nuclear change and SAME shielding
- exception of Al and S
Explain why first ionisation energy of sulphur is lower than predicted from general trend
Electron pair in 3p ORBITAL experiences repulsion
Explain why first ionisation energy of aluminium is lower than predicted from general trend
3p sub shell is shielded better than 3s
Explain trend in reactivity with water down Group 2
- reactivity increases
- shielding increases and outweighs increased nuclear charge
- atomic radius increases
- nuclear attraction decreases
- easier to remove outer electron
Suggest why aluminium is a better conductor of electricity than magnesium
Forms Al3+ compared to Mg2+ so has more delocalised electrons to carry charge
Explain why melting point of S8 is higher than P4
Stronger as sulphur is greater in size so more van der Waals
Explain trend in melting points down Group 2
- decreases
- larger ions so lower charge density
- delocalised electrons are further from positive nucleus
- weaker attraction /metallic bonding
Trend in solubility of metal hydroxides down Group 2
Solubility increases (with Mg(OH)2 only sparingly soluble) and form more alkaline solutions as more OH- dissolves
Trend in solubility of metal sulphates down Group 2
Solubility decreases
Flame Tests for Group 2
Magnesium - white Calcium - brick red / orange Strontium - crimson red Barium - green Atoms emit different wavelengths when they de-excite and fall back to ground state
Trend in thermal decomposition of metal carbonates down Group 2
- decreases
- stability increases down group
- metal ions with a lower charge density have a weaker polarising power
- carbonate ion is less polarised so less likely to separate into oxide ion and carbon dioxide
Standard states of all Group 7 Halogens
F - yellow gas Cl - green gas Br - orange liquid I - black solid At - radioactive
Trend in electronegativity down Group 7
Decreases as atoms are larger so bonding pair is further from positive nucleus and shielding increases
Explain why melting point of Ca is greater than K
- Ca2+ has a higher charge than K+
- more delocalised electrons
- smaller ionic radius
- stronger metallic bonding
Suggest how is sulphur dioxide removed from flue gas
Slurry of CaO/ CaCO3 and water is sprayed on flue gases
Uses of Group 2 metals
Mg to extract Ti from TiCl4
Mg(OH)2 - neutralises stomach acids (milk of magnesia) to cure indigestion
Ca(OH)2- neutralise acidic soils
CaO / CaCO3 - remove sulphur from flue gases
BaSO4 - used as a tracer in medical imaging (barium meal x ray)
Structure of Period 3 elements
Na / Mg / Al = metallic lattice
Si = macromolecule
P4 / S8 / Cl2 = simple
Ar = monoatomic
Suggest ways in which BeCl2 is an atypical example of Group 2 compounds
- high electronegativity so has covalent rather than ionic bonding
- low melting / boiling point due to covalent bonding
- reacts vigorously and exothermically with water
Suggest why BaSO4 is used in medical x rays even though it is toxic
Safe due to low solubility
Suggest why Mg is used in the extraction of Ti from TiCl4
- TiCl4 can be reduced using Mg
- Ti cannot be extracted using carbon as a cheap reducing agent because it forms TiC (titanium carbide) so do not get pure Ti
- TiC = brittle
Describe trend in reactivity with water down Group 2
- Be has no reaction with cold water
- Mg burns in steam (forms MgO white solid and H2 white fumes) and reacts sparingly with water to form alkaline suspension of Mg(OH)2
- Ca / Sr / Ba all react exothermically forming alkaline solution of metal hydroxide (white precipitate) and hydrogen (effervescence)
Suggest a reason for lack of reactivity of beryllium in water
- strong resistant oxide layer on surface
- breaks down at high temperatures (above 700 degrees Celsius)
Suggest why magnesium reacts slowly with water only forming a few bubbles on its surface
- magnesium hydroxide is almost insoluble
- forms barrier preventing further reaction
Suggest why Mg(OH)2 cannot be used in titrations
- sparingly soluble
do not reference pH being too low
Suggest why sulphuric acid cannot be used to acidify barium chloride when testing for sulphates
- barium chloride will react with sulphuric acid
- sulphuric acid contains SO42-
