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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 group 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 remove the first electron (and cause ionisation)
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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)

19
Q

Ca reaction with water

A

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

20
Q

Ca reaction with steam

A

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

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

22
Q

observation for the reaction between magnesium 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 decreases

23
Q
A
24
Q

solubility trend of group 2 sulphates???

A
25
Q

Write the equation & ionic equation & observation for the reaction between
Barium nitrate solution and Sodium sulphate solution

A

white ppt of BaSO4

26
Q

Name one use of barium sulphate which relies upon its insoluble nature

A

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.

27
Q

Describe what the chemical test for sulphates is

A

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.

28
Q

chemical test for sulphates - what does adding HCl do (eqn)

A

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

29
Q

bases

A

bases react with acid to give salt and water
acid + base -> salt + water

30
Q

Magnesium hydroxide as an antacid

A

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

31
Q

Use of Calcium Hydroxide

A

Calcium Hydroxide is used to treat acidic soils
Ca(OH)2 + 2H+ -> Ca2+ +2H2O

32
Q

absorbing acidic products from flue gases

A

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

33
Q

ways of reduction of titanium (IV) chloride

A

Reduction by sodium
Reduction by magnesium

34
Q

reduction of titanium (IV) chloride - Reduction by sodium

A

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

35
Q

reduction of titanium (IV) chloride - Reduction by magnesium

A

The method is similar to using sodium, but this time the reaction is:
TICI4 + 2Mg -> Ti + 2MgCl2

36
Q

Why is titanium so expensive?

A

Titanium is very expensive because it is awkward to extract from its ores - for
example, from rutile, TiO2.

37
Q

extracting titanium from its ores

A

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.

38
Q

Melting points across period 3

A

Na -> Al:
* Increased nuclear charge
* so 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

39
Q

Reaction of P3 elements with oxygen - sodium

A

burns with a yellow flame - white solid forms
2Na (s) + 1/2 O2 (g) -> Na2O (s)

40
Q

Reaction of P3 elements with oxygen - Magnesium

A

burns with a bright white flame - white solid forms
Mg (s) + 1/2 O2 (g) -> MgO (s)

41
Q

Reaction of P3 elements with oxygen - Aluminium

A

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

42
Q

Reaction of P3 elements with oxygen - Silicon

A

burns with a bright white flame
Si (s) + O2 (g) -> SiO (g)

43
Q

Reaction of P3 elements with oxygen - Phosphorus

A

burns with a bright white flame
P4 (s) + 5O2 (g) -> P4O10 (s)

44
Q

Reaction of P3 elements with oxygen - sulfur

A

burns with a blue flame
S (s) + O2 (g) -> SO2 (s)

A level chemistry (8 decks)

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