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Chemistry > Periodicity > Flashcards

Periodicity Flashcards

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1
Q

Trend for first ionisation energies for Period 3 elements

A
  • increases across period due to increasing nuclear change and SAME shielding
  • exception of Al and S
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2
Q

Explain why first ionisation energy of sulphur is lower than predicted from general trend

A

Electron pair in 3p ORBITAL experiences repulsion

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3
Q

Explain why first ionisation energy of aluminium is lower than predicted from general trend

A

3p sub shell is shielded better than 3s

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4
Q

Explain trend in reactivity with water down Group 2

A
  • reactivity increases
  • shielding increases and outweighs increased nuclear charge
  • atomic radius increases
  • nuclear attraction decreases
  • easier to remove outer electron
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5
Q

Suggest why aluminium is a better conductor of electricity than magnesium

A

Forms Al3+ compared to Mg2+ so has more delocalised electrons to carry charge

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6
Q

Explain why melting point of S8 is higher than P4

A

Stronger as sulphur is greater in size so more van der Waals

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7
Q

Explain trend in melting points down Group 2

A
  • decreases
  • larger ions so lower charge density
  • delocalised electrons are further from positive nucleus
  • weaker attraction /metallic bonding
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8
Q

Trend in solubility of metal hydroxides down Group 2

A

Solubility increases (with Mg(OH)2 only sparingly soluble) and form more alkaline solutions as more OH- dissolves

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9
Q

Trend in solubility of metal sulphates down Group 2

A

Solubility decreases

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10
Q

Flame Tests for Group 2

A 
Magnesium - white 
Calcium - brick red / orange 
Strontium - crimson red
Barium - green
Atoms emit different wavelengths when they de-excite and fall back to ground state
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11
Q

Trend in thermal decomposition of metal carbonates down Group 2

A
  • decreases
  • stability increases down group
  • metal ions with a lower charge density have a weaker polarising power
  • carbonate ion is less polarised so less likely to separate into oxide ion and carbon dioxide
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12
Q

Standard states of all Group 7 Halogens

A 
F - yellow gas 
Cl - green gas 
Br - orange liquid 
I - black solid 
At - radioactive
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13
Q

Trend in electronegativity down Group 7

A

Decreases as atoms are larger so bonding pair is further from positive nucleus and shielding increases

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14
Q

Explain why melting point of Ca is greater than K

A
  • Ca2+ has a higher charge than K+
  • more delocalised electrons
  • smaller ionic radius
  • stronger metallic bonding
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15
Q

Suggest how is sulphur dioxide removed from flue gas

A

Slurry of CaO/ CaCO3 and water is sprayed on flue gases

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16
Q

Uses of Group 2 metals

A

Mg to extract Ti from TiCl4
Mg(OH)2 - neutralises stomach acids (milk of magnesia) to cure indigestion
Ca(OH)2- neutralise acidic soils
CaO / CaCO3 - remove sulphur from flue gases
BaSO4 - used as a tracer in medical imaging (barium meal x ray)

17
Q

Structure of Period 3 elements

A

Na / Mg / Al = metallic lattice
Si = macromolecule
P4 / S8 / Cl2 = simple
Ar = monoatomic

18
Q

Suggest ways in which BeCl2 is an atypical example of Group 2 compounds

A
  • high electronegativity so has covalent rather than ionic bonding
  • low melting / boiling point due to covalent bonding
  • reacts vigorously and exothermically with water
19
Q

Suggest why BaSO4 is used in medical x rays even though it is toxic

A

Safe due to low solubility

20
Q

Suggest why Mg is used in the extraction of Ti from TiCl4

A
  • TiCl4 can be reduced using Mg
  • Ti cannot be extracted using carbon as a cheap reducing agent because it forms TiC (titanium carbide) so do not get pure Ti
  • TiC = brittle
21
Q

Describe trend in reactivity with water down Group 2

A
  • Be has no reaction with cold water
  • Mg burns in steam (forms MgO white solid and H2 white fumes) and reacts sparingly with water to form alkaline suspension of Mg(OH)2
  • Ca / Sr / Ba all react exothermically forming alkaline solution of metal hydroxide (white precipitate) and hydrogen (effervescence)
22
Q

Suggest a reason for lack of reactivity of beryllium in water

A
  • strong resistant oxide layer on surface

- breaks down at high temperatures (above 700 degrees Celsius)

23
Q

Suggest why magnesium reacts slowly with water only forming a few bubbles on its surface

A
  • magnesium hydroxide is almost insoluble

- forms barrier preventing further reaction

24
Q

Suggest why Mg(OH)2 cannot be used in titrations

A
  • sparingly soluble

do not reference pH being too low

25
Q

Suggest why sulphuric acid cannot be used to acidify barium chloride when testing for sulphates

A
  • barium chloride will react with sulphuric acid

- sulphuric acid contains SO42-

Chemistry (10 decks)

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