AS.6 Periodicity Flashcards
Periodicity
Repeating patterns and trends across a period of the periodic table
Trends in melting/boiling point across a period - giant metallic lattice structures
General increase
More delocalised electrons and higher ionic charge of cations
Higher electrostatic attraction
Stronger metallic bonds
Trends in melting/boiling point across a period - simple covalent lattice structures
E.g. period 3
P4 S8 Cl2 Ar
S8 P4 Cl2 Ar
All have London forces as strongest IMF
Decreasing number of electrons
S8 has more surface area contact points
Trends in melting and boiling point across period - giant covalent lattice structures
Covalent bonds are strongest
Comparing melting and boiling points across a period
Giant covalent
Giant metallic
Simple covalent
Group 2 reactions
Get oxidised
Lose 2 electrons
Group 2 reactivity down a group
Increases
Atomic radius increase
Shielding increase
Valence electrons further from nucleus
Nucleus attraction decrease
Donate more readily
MgCO3 and Mg(OH)2
Neutralising stomach acids
Ca(OH)2
Neutralising acidified soil
Metal and oxygen
Metal oxide
Metal and water
Metal hydroxide and hydrogen gas
Effervescence
Solid metal disappears
Metal and acid
Salt and hydrogen gas
Effervescence
Solid metal disappears
Metal oxide and water
Metal hydroxide
Solid metal disappears
Halogens reactions
Oxidising agent - electron acceptor
F2
Pale yellow gas
Cl2
Pale green gas
Br2
Red/brown liquid
Halogen oxidising ability trend
Decrease down group
Atomic radius increase
More shielding
Less nucleus attraction to outer electrons
Reactivity decrease
Halogens in solution
Dissolve in water because polar
Chlorine in water and cyclohexane
Water - pale green
Cyclohexane (more soluble) - pale green
Bromine in water and cyclohexane
Water - orange
Cyclohexane- orange
Iodine in water and cyclohexane
Water - dark brown
Cyclohexane- purple
Halogens and halides
If halogen is strong enough oxidiser, it will accept electrons to form halide
The halide will donate electrons to form a halogen
X2 must be more reactive than X-
Halogen colour
Depending on which halogen
Halide colour
Colourless
Disproportionation
When an element is both oxidised and reduced at the same time
Chlorine and water
Cl2 + H2O ———————->HClO + HCl
Chlorine is reduced to HCl and oxidised to HClO
Used to treat water to kill bacteria (ClO-)
Synthesis of bleach
Cl2 + 2NaOH ————> NaClO + NaCl + H2O
Chlorine is reduced to NaCl and oxidised to NaClO
Test for CO3 2-
Add HNO3 (H+)
Effervescence
2H+ + CO3 2- ———-> CO2 (g) + H2O
Test for SO4 2-
Add Ba(NO3)2 or BaCl2 (Ba 2+)
White precipitate
Ba 2+ + SO4 2- ——-> BaSO4 (s)
Test for halides
Add AgNO3 (Ag+)
Precipitate
Ag+ + X- ——-> AgX (s)
Test for chloride
White
Dilute ammonia - dissolves
Concentrated ammonia - dissolves
Test for bromine
Cream
Dilute ammonia - no change
Concentrated ammonia - dissolves
Test for iodide
Yellow
Dilute ammonia - no change
Concentrated ammonia- no change
Order of tests
Carbonates
Sulfates
Halides
Why the order of tests
False positives
When testing for sulfates - rule out carbonate as carbonates will produce precipitate of BaCO3
When testing for halides - rule out sulfate as sulfate would produce precipitate of Ag2SO3
Test for ammonium cation
NH4+
Heat gently with NaOH in boiling tube
Place moist red litmus paper near tube opening
If positive - blue
NH4+ + OH- ———> H2O + NH3
