1.6 Periodicity Flashcards
Explain the trend in IE down a group
- decreases
- more electrons so more shells so more electron shielding which outweighs the increase in nuclear charge, resulting in decreased nuclear attraction meaning less energy is required to remove an outer electron
Explain the trend in IE across a period
- increases
- electrons in same shell so no change in electron shielding but there is a greater nuclear charge as proton number increases so it is harder to lose the outer electron due to greater nuclear attraction
Explain the trend in the melting and boiling points of group 1
- decreases as descend
- metallic bonding held by attraction of nuclei to delocalised electrons
- increase in size due to increased protons means greater distance between therefore weaker attraction so can be more easily pulled apart to liquid/gas
Explain the trend in B+M point in group 7
- increases as you descend
- number of electrons increases resulting in larger induced dipoles and therefore stronger van der waals forces so more energy is required to break
Explain the trend of M+B point across a period
- level attraction between positive nuclei and delocalised electrons increases
- G1-G3 has increased charge due to more delocalised electrons therefore more attraction therefore stronger metallic bonds - more energy to break
- G4 are giant covalent so strong covalent bonds
- G5 sees change from covalent to simple molecular so van der waals need breaking hence decreased energy
- G5-G8 the larger molecules have stronger van der waals due to more electrons
Trends in electronegativity down a group and across a period
- down: decrease due to shielding
- across: increase due to increased nuclear charge
Reaction of lithium with oxygen and water
- oxygen: shiny to dull, slow
- water: effervesce, float around till dissolve
Reaction of sodium with oxygen and water
- oxygen: fast change from shiny to dull
- water: more effervesce, melt to form spherical shape, faster float
Reactions of potassium with oxygen and water
- oxygen: instant change from shiny to dull
- effervesce, burn w lilac flame, move v quick
Lithium flame
Red
Sodium flame
Orange yellow
Potassium flame
Lilac
Magnesium flame
White/colourless
Calcium flame
Brick red
Barium flame
Apple green
Strontium flame
Crimson
Copper flame
Green blue
Trends of group 2
- all G2 nitrates are soluble
- all G2 carbonates are insoluble
- G2 hydroxides increase in solubility as descend
- G2 sulfates decrease in solubility as descend
Colour of barium sulfate ppt
White
Group 2 carbonates
- decompose on heating but produce metal oxide and carbon dioxide gas
- require increased heat to decompose as descend as thermal stability increases
A species is oxidised if …
oxidation number increases
A species is reduced if …
it’s oxidation number decreases
What is a reducing agent?
- metal or negative ion
- donates electrons to another element
- is oxidised itself
What is an oxidising agent?
- non-metal or positive ion
- cause oxidation reactions
- is reduced itself
Solubility of G1 compounds
- all soluble
Reaction of G1 metals with acid
- metal salt and water
- react more strongly than G2
Solubility of G2 nitrates and carbonates
- nitrates are soluble
- carbonates are insoluble
G2 sulfates trend
- less soluble as you descend
G2 hydroxides trend
- more soluble as you descend
- due to lower attraction between OH- ions and 2+ as atom increases in size and so can be split easier
G2 thermal stability trend
- increases as you descend so more heat energy required as you descend
How do you identify halides? Give relevant colours
- add silver nitrate
- chloride = white
- bromide = cream
- iodide = yellow brown
How do you identify magnesium compounds?
- add sulphuric acid
- if magnesium present it gives solution, if not then a solid forms
How do you identify barium compounds?
- add sodium hydroxide
- if barium present a solution forms, if not a solid forms
Reaction of Mg with HCL
- effervesce
- Mg dissolve into solution
Describe trend in reactivity of G2 metals with water
- reactivity increase as descend
- more shells so more shielding so decreased nuclear attraction (outweighs nuclear charge)
- IE decreases
How to prepare solution of sodium and carbonate
- weigh appropriate mass of solid
- dissolve mass in small volume of deionised water
- add solution to 250cm3 volumetric flask using funnel
- shake to mix
Why might strongly heating carbonates be an issue when measuring their end mass?
- some may begin to decompose
- lead to lower mass recorded
How could you test for the presence of carbonate?
- add an acid
- observe effervescence if carbonate present
How could you test for sulfate ions?
Add barium chloride and look for a ppt
Define volatility
- how easily something can be vaporised
- higher BP = harder to vaporise so lower volatility
Explain reactivity trend in G7
- decreases
- increased nuclear charge blocked by increased electron shielding as distance between nucleus and outer shell increases, causing attraction to decrease which makes it harder to add an electron
… reactive halogen displaces a … reactive halogen
- more
- less
Define oxidising power
The power an element has to gain an electron
Explain G7 in terms of oxidising agents
- chlorine has ability to take electrons from both bromide and iodide ions. Bromine and iodine cannot reclaim these electrons which indicates that chlorine is a more powerful oxidising agent than Br and I
- bromine more powerful oxidising agent than iodine as it can remove electrons from iodine that iodine cannot reclaim
Explain G7 in terms of reducing agents
- halide ions are good reducing agents as they donate electrons and are themselves oxidised
- reducing power increases down group as electrons are easier to lose from larger ions due to decreased nuclear attraction
Explain the origin of the colours in flame tests
Excited electrons move down energy levels
Explain the term oxidising agent in terms of electron transfer
Metal or negative ion that removes electrons
Explain the decrease in atomic radii across periods
- increase protons
- electrons added to same shell
- shielding remain same so greater attraction to nucleus
What is gravimetric analysis
A quantitive method for accurately determining the amount of a substance by selective precipitation of the substance from an aqueous solution
A solution contains sodium chloride and sodium iodide. Added silver nitrate and then ammonia. Explain what occurred during this test
- yellow ppt for iodide and white for chloride
- on adding ammonia and shaking, white ppt dissolves which leaves yellow iodide ppt.
How to obtain magnesium carbonate from a known mass of magnesium
- add acid in excess to ensure all Mg react, forming a salt
- add soluble carbonate in excess so that all Mg2+ ions precipitate
- filter and dry
State results of ammonia test for halide ions
AgCl: ppt dissolve to give colourless solution
AgBr: unchanged if dilute but dissolve if concentrated
AgI: ppt insoluble
