periodicity Flashcards
what elements are in the s-block
groups 1 and 2
what elements are in the p-block
groups 3 to 0
what elements are in the d-block
the transition metals
what elements are in the f-block
radioactive elements
how does atomic radius change along a period
-decreases
-increased nuclear charge, same shielding means electron shells are pulled in closer to the nucleus as there is a stronger attraction between the positive nucleus and the negative electrons.
how does atomic radius change down the group
-increases
-more electron shells increasing the distance between the outer electrons and the nucleus, reducing the power of attraction. electron shielding decreases attraction further
how does ionisation energy change along a period
-increases
-the decreasing atomic radius and increasing nuclear charge means the attraction between the nucleus is stronger. therefore, more energy is required to remove the outer electrons
how does ionisation energy change down the group`
-decreases
-more electron shells, more shielding and increasing distance between outer electrons and nucleus, reducing attraction. less energy needed to remove outer electron
trend for the solubility of group 2 hydroxides
-increases down the group
-Mg(OH)2 is sparingly soluble
trend for the solubility of group 2 sulfates
-decreases down the group
what is a use for magnesium
the extraction of titanium
TiCl4(l) + 2Mg(s) –> 2MgCl2(s) + Ti(s)
what is a use for magnesium hydroxide
to treat indigestion as it neutralises stomach acids
Mg(OH)2 + 2HCl MgCl2 + 2H2O
use for calcium hydroxide
treats acidic soil
use for calcium oxide/carbonate
removes SO2 from flue gases
CaO + SO2 –> CaSO3
use for barium sulfate
medical x-rays
reaction of magnesium with steam
-bright white light and white solid formed
-Mg + H2O –> MgO + H2
reaction of calcium with water
-effervescence and white precipitate formed
-Ca + 2H2O –> Ca(OH)2 + H2
how to test for the presence of sulfate ions
-acidify the sample with HCl to remove carbonate ions as they can form a white precipitate and give a false positive.
-then add barium chloride solution
-a white ppt will form is sulfate ions are present
what is the appearance of the halogens
fluorine- pale yellow gas
chlorine- green gas
bromine- red/brown liquid
iodine- black solid
electronegativity down group 7
-the power of an atom to attract a pair of electrons in a covalent bond
-decreases
-more shells = more shielding
-atomic radius increases so outer e-s are further away from the nucleus
-less attraction between positive nucleus and outer e-s ina covalent bond
boiling point down group 7
-increases
-size of atom increases
-larger atoms have more electrons- stronger VDW forces - more energy needed
oxidising ability of halogens
-decreases
-they accept electrons
-down the group, the atomic radius is greater and there is more shielding - harder to gain e-
reducing ability of HALIDES
-increases
-they donate electrons
-larger atomic radius and more shielding - easier to lose e-
what happens if you add chlorine solution to potassium bromide solution
the solution turns from colourless to orange as the chlorine has displaced the bromine, proving that it is more reactive. potassium chloride and chlorine is formed.
what happens if you add bromine solution to potassium iodide solution
the solution turns brown so bromine has displaced the iodine.
testing for metal halides
-add nitric acid and silver nitrate solution
-AgF produces no ppt
-AgCl produces white ppt
-AgBr produces cream ppt
-AgI produces yellow ppt
as it may be difficult to differentiate between the different ppts, add aqueous NH3. as the solubility of silver halides in ammonia decreases down the group, the AgCl ppt dissolves in dilute NH3, the AgBr ppt dissolves in concentrated NH3 and the AgI ppt is insoluble in NH3.
why is nitric acid used
-removes carbonate ions which may give a false positive as it forms a precipitate
-HCl can’t be used as it contains chloride ions that will form a white ppt
the reaction of sodium chloride with concentrated sulfuric acid
-Cl- is not a strong reducing agent so it is not oxidised by H2SO4
-only an acid-base reaction takes place and HCl gas is formed
H2SO4 + Cl- –>HSO4- + HCl
-white fumes of HCl will be seen
-the fumes will turn blue litmus paper red
-sodium hydrogen sulphate is the other product
the reaction of sodium bromide with concentrated sulfuric acid
-Br- is a better reducing agent than Cl- but the sulphur in the H2SO4 is only reduced from +6 to +4 (SO2)
-the acid-base reaction may also take place
H2SO4 + Br- –> HSO4- + HBr (acid base)
H2SO4 +2H+ + 2Br- –> SO2 + Br2 + 2H2O (redox)
-white fumes (HBr) will be seen which turns blue litmus paper red
-red/brown bromine vapour will also be seen
the reaction of sodium iodide with concentrated sulfuric acid
-I- is a good reducing agent, reducing the sulfur in the H2SO4 from +6 to +4 (SO2), to 0 (S), or to -2 (H2S).
-the acid-base reaction may also take place
H2SO4 + 6H+ + 6I- –> S + 4H2O + 3I2
H2SO4 + 8H+ + 8I- –> H2S + 4I2 + 4H2O
-white fumes (HI) will be seen which turns blue litmus paper red
-the purple colour of iodine vapour will also be seen
-rotten egg smell due to H2S
equation to make bleach
2NaOH + Cl2 –> NaCl + NaClO + H2O
reaction of chlorine with water
Cl2 + H2O <–> HCl + HClO
in sunlight: 2Cl2 + 2H2O <–> 4HCl + O2
benefits and risks of chlorine
-kills disease-causing micro organisms
-eliminates bad tastes and smells
-harmful if breathed in
-toxic
