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A level chemistry > periodicity > Flashcards

periodicity Flashcards

1
Q

what does all members of a group have in common?

A

Same number of electrons in the outer shell i.e. same outer electron configuration e.g. For group 2: ns2

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2
Q

what does all members of a period have in common?

A

Same number of electron shells i.e. filling the same outer shell as you traverse a period e.g. For period 3: filling 3rd Shell

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3
Q

periodicity

A

study of patteren / trends within the periodic table

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4
Q

How would you expect 1st ionisation energies to change going down the group 2
and why

A
  • distance between outer e- and nucleus increases
  • more shielding due to insulating affect of inner electrons
  • weaker electrostatic forces of attraction between nucleus and outer electrons
  • less energy is needed to remove the first electron (and cause ionisation)
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5
Q

How would you expect atomic radius to change going down
the group and why

A

Atoms have more electrons
more electron shells are occupied
distance between outer e- and nucleus increases
atomic radius increases

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6
Q

How would you expect melting point to change going down the group and why

A
  • distance between outer e- and nucleus increases
  • more shielding due to insulating affect of inner electrons
  • weaker electrostatic forces of attraction between cations and sea of delocalised electrons
  • less energy is needed to break apart the ionic lattice
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7
Q

How would you expect electronegativity to change going down the group and why

A
  • distance between outer e- and nucleus increases
  • more shielding due to insulating affect of inner electrons
  • weaker electrostatic forces of attraction between nucleus and a bonding pair of elecrons
  • lower electronegativity
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8
Q

Reactions of group 2 elements with water.
Comment on the vigour of reaction of group 2 metals with water and the trend shown going down group 2 - explain this trend in terms of electronic arrangement

A

Metals get oxidised (lose e-): M -> M2+ + 2e-
* distance between outer e- and nucleus increases
* more shielding due to insulating affect of inner electrons
* weaker electrostatic forces of attraction between nucleus and outer electrons making them easier to lose
* therefore metals get more reactive as you progress down group 2.

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9
Q

Write the general equation for the reaction between group 2 metals and water (M=any group 2 metal)

A

M + 2H20 -> M(OH)2 + H2

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10
Q

Why are the solutions formed alkaline in character?

A

hydroxide ions are formed
(OH-)

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11
Q

Mg reaction with water / steam

A

Mg + 2H2O (l) -> Mg(OH)2 + H2
Mg + H2O (g) -> MgO + H2

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12
Q

Why do the pH of the group 2 hydroxides increase in pH going down the group?

A
  • number of e- shells increases
  • more shielding due to insulating affect of inner electrons
  • weaker electrostatic forces of attraction between group 2 ion and OH- ions
  • easier to dissociate so more OH- ions are released into solution increasing the PH
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13
Q

Na reaction with Oxygen

A

Burns brightly with a yellow flame. Forms a white powder as a product.
4Na (s) + O2 (g) -> 2Na2O (s)
Oxide formed - Na is Oxidised

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14
Q

Na reaction with water

A

Na floats on water, effervescence, gradually dissolves, forms an alkali solution
2Na (s) + 2H2O (l) -> 2NaOH (aq) + H2 (g)

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15
Q

Mg reaction with oxygen

A

Burns with a bright white flame - white powder produced
2Mg (s) + O2 (g) -> MgO (s)
Mg is oxidised

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16
Q

Ca reaction with oxygen

A

Burns with a orange (brick red) flame - white powder produced
2Ca (s) + O2 (g) -> CaO (s)
Ca is oxidised

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17
Q

Mg reaction with water

A

Very slow bubbles of H2 seen on Mg ribbon
Mg (S) + 2H2O (l) -> Mg(OH)2 (s) +H2 (g)

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18
Q

Mg reaction with steam

A

Burns with brilliant white flame - H2 burns if ignited
Mg (S) + H2O (g) -> MgO (s) +H2 (g)

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19
Q

Ca reaction with water

A

Vigourus reaction - white circles form along the tube -white /milky product
Ca (S) +2H2O (l) -> Ca(OH)2 (s) +H2 (g)

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20
Q

Ca reaction with steam

A

Burns with orange (brick red) flame - very vigorous reaction
Ca (S) + H2O (g) -> CaO (s) +H2 (g)

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21
Q

Write the equation & ionic equation & observation for the reaction between magnesium chloride solution and sodium hydroxide solution

A

MgCl2 (aq) + 2NaOH (aq) -> Mg(OH)2 (s) +2NaCl(aq)

Mg2+ (aq) + 2OH- (aq) -> Mg(OH)2 (s)

White ppt of Mg(OH)2 formed

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22
Q

observation for the reaction between Barium chloride solution and sodium hydroxide solution

A

Remains a colourless solution - no ppt as Ba(OH)2 is more soluble as Ba is further down group 2:
As you descend group 2:
* number of e- shells increases
* more shielding due to insulating affect of inner electrons
* weaker electrostatic forces of attraction between group 2 ion and OH- ions
* ability to dissociate (solubility) therfore increases

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23
Q

solubility trend of group 2 sulphates

A

Become less soluble as you descend the group

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24
Q

solubility trend of group 2 Carbonates

A

Become less soluble as you descend the group

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25
solubility trend of group 2 Hydroxides
Become more soluble as you descend the group
26
Write the equation & ionic equation & observation for the reaction between Barium nitrate solution and Sodium sulphate solution
white ppt of BaSO4
27
Name one use of barium sulphate which relies upon its insoluble nature
Used in barium meals for aiding diagnosis of problems of gastro - intestinal tract. BaSO4 (s) is drunk as a suspension - coats the intestinal tract and acts as contrast medium to hightlight any abnormalities of soft tissue.
28
Describe what the chemical test for sulphates is
Add HCl to prevent the formation of unwanted white precipitates e.g. BaCO3 or Ba(HCO3)2 which would also give a false positive. Add mixture of BaCl2 to an unknown compound. If the unknown compound is a sulfate - it will produce a white ppt of BaSO4.
29
chemical test for sulphates - what does adding HCl do (eqn)
Without HCl added: BaCl2 (aq) + Na2CO3 (aq) -> BaCO3 (s) + 2NaCl (aq) Adding HCl after reaction: BaCO3 (aq) + 2HCl (aq) -> BaCl2 (aq) + CO2 + H2O Adding HCl before reaction: Na2CO3 (aq) + 2HCl (aq) -> 2NaCl (aq) + CO2 + H2O BaCl2 (aq) + Na2SO4 (aq) -> BaSO4 (s) + 2NaCl (aq)
30
bases
bases react with acid to give salt and water acid + base -> salt + water
31
Magnesium hydroxide as an antacid
milk of magnesia is an antacid containg a suspension of Mg(OH)2 (particles of insoluble solid suspended in a liquid). This allows it to relieve indigestion- since it is a base and reacts with excess acid in stomach to neutralise its acid: Mg(OH)2 + 2HCl -> MgCl2 + 2H20
32
Use of Calcium Hydroxide
Calcium Hydroxide is used to treat acidic soils Ca(OH)2 + 2H+ -> Ca2+ +2H2O
33
absorbing acidic products from flue gases
when fossil fuels are burnt SO2 is produced S (s) + O2 -> SO2 (g) SO2 can cause acid rain Flue gases from power stations are often passed through filter beds of calcium oxide / Calcium carbonate: CaO + SO2 -> CaSO3 CaCO3 + SO2 -> CaSO3 + CO2
34
ways of reduction of titanium (IV) chloride
Reduction by sodium Reduction by magnesium
35
reduction of titanium (IV) chloride - Reduction by sodium
The titanium (IV) chloride is added to a reactor in which very pure sodium has been heated to about 550C - everything being under an inert argon atmosphere. During the reaction, the temperature increases to 1000C TICI4 + 4Na -> Ti + 4NaCl After the reaction is complete, and everything has cooled (several days in total - an obvious inefficiency-of the batch process), the mixture is crushed and washed with dilute hydrochloric acid to remove the sodium chloride
36
reduction of titanium (IV) chloride - Reduction by magnesium
The method is similar to using sodium, but this time the reaction is: TICI4 + 2Mg -> Ti + 2MgCl2
37
Why is titanium so expensive?
Titanium is very expensive because it is awkward to extract from its ores - for example, from rutile, TiO2.
38
extracting titanium from its ores
Titanium can't be extracted by reducing the ore using carbon as a cheap reducing agent as titanium will react with carbon to produce Titanium carbide making the metal more brittle.
39
measuring atomic radius - the covalent radius
distance between the center of 2 adjacent atoms (which are covalently bonded) and half the distance
40
Melting points across period 3
Na -> Al: * Increased nuclear charge * so stronger electrostatic forces of attraction between Nuclueus and sea of delocalised electrons * Increasing melting point greater availability of delocalised electronsfrom each metal 1-3 to join the sea of delocalised electrons - causes stronger electrostatic forces of attraction between Nuclueus and sea of delocalised electrons * Increasing melting point Si: Giant covalent - many strong covalent bonds - highest mp of group 3 elements forming a peak here P4 - drop from Si to P as P has only weak van der walls forces holding them together compared to Si's many strong covalent bonds S8 - Mp increases as size of molecule increases so SA increases so strength of van der walls forces increases Cl2 - Mp decreases as size of molecule decreases so SA decreases so strength of van der walls forces decreases Ar - Mp decreases as size of molecule decreases so SA decreases so strength of van der walls forces decreases
41
Reaction of P3 elements with oxygen - sodium
burns with a yellow flame - white solid forms 2Na (s) + 1/2 O2 (g) -> Na2O (s)
42
Reaction of P3 elements with oxygen - Magnesium
burns with a bright white flame - white solid forms Mg (s) + 1/2 O2 (g) -> MgO (s)
43
Reaction of P3 elements with oxygen - Aluminium
burns with a bright white flame - white solid forms 2Mg (s) + 3O2 (g) -> 2Al2O3 (s) Aluminium doesn't appear to react with oxygen due to an oxide layer forming on it
44
Reaction of P3 elements with oxygen - Silicon
burns with a bright white flame Si (s) + O2 (g) -> SiO2 (s)
45
Reaction of P3 elements with oxygen - Phosphorus
burns with a bright white flame P4 (s) + 5O2 (g) -> P4O10 (s)
46
Reaction of P3 elements with oxygen - sulfur
burns with a blue flame S (s) + O2 (g) -> SO2 (s) SO3: done in high temperatures 2S (s) + 3O2 (g) -> 2SO3 (s) Catalyst: V2O5 Platinum Fe2O3
47
Acid-Base Character of period 3 oxides - pH in water
Generally the pH of solutions in water of period 3 oxides gradually decreases from left to right.
48
Acid-Base Character of period 3 oxides - Na2O
Na2O dissolves in water to produce NaOH which has a pH of approx 14 depending on concentration of OH - ions produced. Na2O (s) + H20 (l) -> 2 NaOH (aq) O2- + H20 -> 2 OH-
49
Acid-Base Character of period 3 oxides - MgO
MgO is only sparmgls soluble in water so only a small amount dissolves to produce only a small number of aqueous OH - ions and therefore the [OH- ] ions is low and so pH consequently is approx 8 / 9. MgO (s) + H2O (l) -> Mg(OH)2 (aq) O2- + H20 -> 2 OH-
50
Acid-Base Character of period 3 oxides - Al2O3
AI203 is insoluble in water and therefore the pH of water is 7 ie no OH - ions ( or H+ ions ) are produced
51
Acid-Base Character of period 3 oxides - SiO2
SiO2 is insoluble in water and therefore the pH of water is 7 ie no OH - ions ( or H+ ions ) are produced
52
Acid-Base Character of period 3 oxides - P4O10
P4O10 can react with water to form phosphoric acid (H3PO4) - which can dissociate to give a high concentration of H+ ions and so solution has a pH of approx 1. P4O10 + 6 H20 -> 4H3PO4 H3PO4 -> H+ + H2PO4-
53
Acid-Base Character of period 3 oxides - SO2
SO2 react with water to form sulphuric (IV) acid. These dissociate to produce H+ ions and so pH is 3. H2SO3 - weak acid - only partially dissociates - lower conc. of H+ ions - highter PH of 3 SO2 + H2O -> H2SO3 -> H+ + HSO3 -
54
Acid-Base Character of period 3 oxides - SO3
SO3 react with water to form sulphuric (VI) acid. These dissociate to produce H+ ions and so pH is 0 / 1. H2SO4 - strong acid - fully dissociates - higher conc. of H+ ions - lower PH of 0/1 SO3 + H2O -> H2SO4 -> H+ + HSO4 -
55
Reactions of period 3 oxides with acids and bases - Na2O
Na2O is a BASE and consequently reacts with ACIDS form salts + H2O: Na2O + 2HCl -> 2NaCl +H2O O2- + 2H+ -> H2O
56
Reactions of period 3 oxides with acids and bases - MgO
MgO is a BASE and consequently reacts with ACIDS form salts + H2O: MgO + 2HCl -> MgCl2 +H2O O2- + 2H+ -> H2O
57
giant covalent
carbon - diamond, graphite Si SiO2
58
Oxidation states of period 3 elements
Na +1 Mg +2 Al +3 Si +4 P +5 S +4, 6
59
Reactions of period 3 oxides with acids and bases - Al2O3
Al2O3 is unusualin that it can behave as both an acid and a base - it is amphoteric Al2O3 as a base: Al2O3 + 2HCl -> AlCl3 + 3H2O O2- + 2H+ -> H2O Al2O3 as a Acid: Al2O3 + 2NaOH + 3H2O -> 2Na[Al(OH)4] Al2O3 + 2OH- + 3H2O -> 2[Al(OH)4]-
60
Reactions of period 3 oxides with acids and bases - Al(OH)3
Similarly Aluminium hydroxide Al(OH)3 is amphoteric and can both dissolve in acid and alkali in a similar way to aluminium oxide: Al(OH)3 as a base: 2Al(OH)3 + 3H2SO4 -> Al2(SO4)3 + 6H2O O2- + 2H+ -> H2O Al(OH)3 as a acid: Al(OH)3 + KOH -> K[Al(OH)4] Al(OH)3 + OH- -> [Al(OH)4]-
61
Reactions of period 3 oxides with acids and bases - SiO2, P4O10, SO2, SO3 - **LEARN WELL AND DO ON PAPER**
SiO2, P4O10, SO2 and SO3 are all acidic oxides and will therefore react with OH - ions from bases like NaOH to form salts + water as shown below - full equations:
62
63
**do on paper**
64
Name of Process of removing toxic SO2
Desulfurisation
65
Magnesium burns with a bright light and is used in flares and fireworks. Using knowledge of reactions of group 2 metals with water, explain why water shouldn’t be used to put out a fire in which magnesium metal is burning.
Adding water causes the following reaction: Mg + H2O (g) -> MgO (g) + H2 (g) Produces H2 which is flammable and dangerous.

A level chemistry (15 decks)

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