Group 2+7 Flashcards
Why does a flame test work
When metal compound is heated electrons in the metal ion are excited to a higher energy level
As electrons return to normal energy level the energy is emitted as visible light
The colour of light emitted is due to the energy gap
How does solubility of hydroxides change down the group
Hydroxides increase in solubility down the group
How do sulfates change in solubility down the group
Sulfates decrease in solubility down the group
Formula of a metal sulfate
XSO4
Formula of group 2 hydroxide
X(OH)2
Flame test colour of lithium
Crimson
Flame test colour of sodium
Yellow
Flame test colour of potassium
Lilac
Flame test colour of beryllium
No change
Flame test colour of magnesium
No change
Flame test colour of calcium
Brick red
Flame test colour of strontium
Red
Flame test colour of barium
Green
Why does thermal stability of group 2 carbonate change
As you go down group 2 ionic radius increases
Therefore charge density increases
Less able to polarise carbonate ion
Therefore more energy required to break C-O bond
What is thermal decomposition
The breaking down of a substance using heat energy
Is exothermic
Properties of group 7 elements
Non-metal
Reactive
Not found natively (as pure elements)
Usually found in compounds with metals eg halide salts
How does the reactivity of group 7 elements change down the group
Less reactive down the group
Why does reactivity change down group 7
Halogens form 1- ion by gaining outer shell electron
Further out outer shell makes it harder to gain an electron
Why is ionic radii greater than atomic radii group 7
Because an electron has been gained and now more electrons than protons
Hence attraction between nucleus and each electron decreases
Change in melting/boiling of group 7 and why
Increase down the group
Only London forces so bigger molecule creates stronger forces so more energy required to break
Why do all halogens have similar chemical properties
All react to gain one outer shell electron
Are group 7 elements oxidising or reducing agents
Tend to gain electrons in reaction so are likely to be oxidising agents and be reduced
When will group 7 element not have negative oxidation state
When combined with oxygen as oxygen is more electronegative
How does oxidising ability change down group 7
Decreases
Ability to gain electrons decreases down group as number of shells increases so outer electron further from nucleus and more shielding
Why are group 7 poorly soluble with water
Unable to form hydrogen bonds with water so can’t release enough energy to overcome hydrogen bonds between water molecules
Why are group 7 soluble in cyclohexane
Both have London forces as strongest intermolecular bonds
Energy released by forming London forces between halogen and solvent releases enough energy to break London forces between halogen and solvent
Physical state at room temp for Cl, Br and I and why
Cl- gas
Br- liquid
I- solid
Increase in number of electrons so increase in strength of London forces
Why has hydrogen flouride got higher boiling point than expected
Has intermolecular hydrogen binding and therefore intermolecular forces require more energy to break
What happens in redox reaction of group 7 and 1/2 metal
Electrons transferred from metal to halogen to form metal halide
Appearance of metal halide
Generally white solid
What happens in reaction of chlorine and water
Produces a mixture of two acids
H2O + Cl2 becomes HCl and HOCl
Why does redox chlorine and water form two acids
Cl is oxidised to form HOCl and reduced to form HCl
Reaction of chlorine and COLD alkali
Forms sodium chlorate (I)
Cl2 + 2NaOH becomes NaCL + NaClO + H2O
Reaction of chlorine and HOT alkali
Forms sodium chlorate (V)
3Cl2 + 6NaOH becomes 5NaCl + NaClO3 + 3H2O
What is hydrogen halide displacement
A more reactive halogen will take the place of a less reactive halogen
Reactivity of halogens from most reactive to least
Fluorine
Chlorine
Bromine
Iodine
What does bromine dissolve in
An organic solvent
Precipitate colour reaction of silver nitrate and chlorine
White
Precipitate colour reaction of silver nitrate and bromine
Cream
Precipitate colour reaction of silver nitrate and iodine
Yellow
How to differentiate between yellow and cream precipitate
Silver bromine (cream) will not dissolve in aqueous ammonia but will dissolve in conc ammonia
Silver iodide (yellow) is insoluble in both aqueous and conc ammonia
Therefore add concentrated ammonia
Basic ionic formula for silver nitrate and halogen
Ag+(aq) + X-(aq) becomes AgX (s)
Result of adding aqueous barium chloride followed by dilute hydrochloride acid
White pot insoluble in hydrochloric acid
SO42- ions present
Result of adding dilute acid to compound
Effervescence giving colourless gas and gas turning water guilty = CO3 2- ions present
Pungent colourless gas on warming that decolourises potassium manganate = SO3 2- ions present
Result of adding aqueous sodium hydroxide and heat
Gas that turns damp red litmus paper blue means NH4+ ions present
Result of adding aqueous sodium hydroxide
White precipitate insoluble in excess reagent means insoluble metal hydroxide- group 2 metal ions likely
Result of warm solid with aqueous sodium hydroxide and aluminium/zinc powder
Gas that turns damp red litmus paper blue means NO3- ions present reduced to NH3
