CH4: Inorganic Chemistry + Periodic Table Flashcards
Trend of ionisation energy down group 2? How does this explain the reactivity trend down the group?
DECREASES:
Extra inner shells shield outer electrons from attraction to nucleus
- also larger atomic radius down the group —> less electrostatic attraction to nucleus
The higher the first/second ionisation energies - need more energy to lose an electron - so *less likely to lose electron —> less reactive
Ionisation energy decreases, reactivity increases
Group 2 reactions with water, oxygen ad chlorine ?
WATER : M + 2H20 —> M(OH)2 + H2
Metal hydroxide and hydrogen (beryllium oxide doesn’t react with water)
OXYGEN : 2M +O2 —> 2MO
Form oxides
CHLORINE : M + Cl2 —> MCl2
Form chlorides
Magnesium’s reactions with water?
Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)
- reacts extremely slowly in cold water (mg hydroxide and hydrogen)
- Solution formed is weakly alkaline (pH 9-10) as magnesium hydroxide is only slightly soluble
- magnesium is heated in steam, forms magnesium oxide and hydrogen gas:
Mg (s) + H2O (g) → MgO (s) + H2 (g)
Why do the oxides form more strongly alkaline solutions down the group ?
Hydroxides get more soluble
Group 2 oxides reaction with dilute acid?
MO + 2HCl —> MCl2 + H2O
Reaction with HCl : forms chloride + water
Reaction with sulphuric acid : forms sulfate + water
Hydroxide reactions with water and dilute acid?
M(OH)2 (s)+ H2O —-> M(OH)2 (aq)
Solubility trends of group 2?
Compounds of group 2 elements that contain single charged negative ions (OH-) INCREASE in solubility down the group - ALSO INCREASES ALKALINITY
Compounds with double charged negative ions (SO4 2-) decrease in solubility down the group
What is thermal decomposition?
the breakdown of a compound into two or more different substances using heat
What do group 1/2 carbonates decompose into?
GROUP 1 : thermally stable , so Bunsen can’t make them decompose (EXCEPT LITHIUM CARBONATE —> forms lithium oxide/co2 )
GROUP 2 : Metal oxide and carbon dioxide gas
How do group 1/2 nitrates decompose ?
GROUP 1 : Decompose to form metal NITRITE (NO2 -) /oxygen
Except lithium nitrate : forms nitrogen dioxide , lithium oxide and oxygen
2LiNO3 —> 2NO2 + Li20 + 1/2 O2
GROUP 2: forms oxide, nitrogen dioxide (toxic), and oxygen
Why does the thermal stability of group 1/2 increase down the groups?
Cation ( + ions) POLARISE the anions (- ions - nitrate /carbonate ions) , distorting it
The greater the distortion , the less stable it is
LARGER CATIONS CAUSE LESS DISTORTION THAN SMALLER CATIONS, bc they have lower charge density
- down the group, cations are larger, so less charge density and less distortion caused —> MORE STABLE
Why are group 2 compounds less thermally stable than group 1 compounds?
Group 2 have 2+ charge
The greater the charge on the cation, Polarises anion more, greater the distortion —> C-O or N-O bond weakened more - anions become less stable
How to carry out flame tests?
- Pass piece of platinum/Nichrome wire in hot Bunsen flame
- Dip wire into fresh hydrochloric acid - forms volatile chlorides
- Dip wire into solid compound /place in flame
Flame colours of group1/2 metals?
Li , Na, K, Rb, Cs, Ca, Sr, Ba
Li - red
Na- orange/yellow
K - lilac
Rb - red
Cs - blue
Ca- brick red
Sr- crimson
Ba - green
What causes the flame colours ?
Electrons get excited and move to higher energy kevel
As electron returns to lower energy levels, they release energy in form of light
- the difference in energy between the higher/lower levels determines the wavelength of light released -
Different energy gaps so different colour emitted
Halogen colours down the group?
F,cl, br,i
F2 - pale yellow gas
Cl2 - green/yellow gas
Br2 - orange /brown liquid
I2 - grey/black solid , purple vapour
Why do Mp/Bp increase down group 7?
Increase in electron shells down the group, STRONGER LONDON FORCES
- harder to overcome, so higher MP/BP
As MP/BP increase down the group, the volatility decreases
- it iS more volatile if its easier to evaporate (lower BP)
Trend in electronegativity down group 7 ?
How strongly atoms attracts electrons to itself in a covalent bond
ELECTRONEGATIVITY DECREASES down the group as:
- atomic radii increase down group (outer shells further for nucleus ) —> less attraction to nucleus
- more shielding down the group
Harder to attract electron (oxidising power) decreased
Why does reactivity decrease down group 7?
Halogens reacts by GAINING AN ELECTRON (-1 IONS)
- so has been reduced/acts an oxidising agent
As you go down group :
Atomic radii increases/shielding increases, so less attraction to nucleus —> harder to attract electrons
How can displacement reactions show the more reactive halogen /best oxidising agent?
Chlorine will displace both bromine/iodine
- so is therefore REDUCED itself (gain electrons) , but acts as an oxidising agent (oxidises bromine/iodine)
Observations when chlorine reacts with halides (potassium bromide or potassium iodide)
And what happens when organic solvent is added?
Chlorine + Potassium Bromide :
Solution become YELLOW - ORANGE (bromine formed)
Cl2 + 2Br - —> 2Cl- + Br2 ( Chlorine is reduced , gains electrons as it displace bromine)
IF ORGANIC SOLVENT ADDED : layer will be yellow orange
Chlorine + Potassium Iodide:
Solution becomes brown (iodine formed)
Cl2 + 2I - —> 2Cl- + I2
IF ORGANIC SOLVENT ADDED : layer will be PURPLE
Halogen reactions with group 1/2 metals ?
Form ionic compounds which are halide salts
2Na + Cl2 —> 2NaCl
Na is oxidised , bc oxidation no goes from 0 to +1
SO HALOGENS ACT AS OXIDISING AGENTS
Halogen reactions with Iron ?
Chlorine/bromine can oxidise iron (II) to iron (III)
However, iodine is oxidised from iodide ions when reacted with iron
What is a disproportionate reaction?
Example of this in cold DILUTE alkalis?
Reaction where the same species is both oxidised/reduced
Cold alkalis :
Cl2 + 2NaOH —> NaCl + NaClO + H20
Forms sodium chlorate(I) - used for bleach
Ionic equn: Cl2+ 2OH- —> Cl- + ClO-+ H20
Chlorine is oxidised(OX number goes from 0 TO +1 ) for Cl2 to ClO-
Chlorine is reduced (OX number goes from 0 to -1) for Cl2 to Cl-
