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Chemistry Unit 5 > Periodicity > Flashcards

Periodicity Flashcards

1
Q

Explain the trend in electronegativities across Period 3

A
  • Electronegativitiy is the ability of an atom to attract a bonding pair of electron
  • Electronegativity increases across period
  • Proton number increases so increase in nuclear charge
  • Same number of electron shells so constant shielding
  • Attraction of bond pair to nucleus increases
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2
Q

Using electronegativity, why does Na2O and P4O10 have different melting points

A
  • When there’s a big difference in electronegativity, ionic bonding occurs
  • Smaller difference is covalent bond
  • Na2O is an ionic lattice
  • Strong elec forces of attraction between opp-charged ions
  • P4O10 is a simple covalent molecule
  • There are weak intermolecular forces between molecules
  • melting point Na2O greater than for P4O10
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3
Q

Explain the high mp of SiO2 and why is it insoluble

A
  • Macromolecule
  • Many strong covalent bonds to be broken
  • lots of energy required to break bond
  • Water cannot supply enough energy to break the covalent bonds
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4
Q

Observations when Mg burns in O2 and when the oxide is added to water

A
  • Bright White flame
  • White Solid formed
  • pH 10
  • MgO + H2O → Mg(OH)2
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5
Q

Observations when Na burns in O2 and when the oxide is added to water

A
  • Yellow flame
  • White solid formed
  1. vigorous reaction;
  2. forms a colourless solution;
  3. pH of solution formed = 13/14;
  4. Na2O + H2O → 2NaOH;
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6
Q

Observations when Al burns in O2 and when the oxide is added to water

A
  • Normal flame
  • The layer of Al2O3 is insoluble
  • No reaction pH 7
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7
Q

Observations when P burns in O2 and when the oxide is added to water

A
  • White flame
  • Clouds of white smoke is formed
  1. vigorous reaction;
  2. forms a colourless solution;
  3. pH of solution formed = 0 or 1;
    P4O10 + 6H2O →¨ 4H3PO4;
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8
Q

Observations when S burns in O2 and when the oxide is added to water

A
  • Blue flame
  • Smelly and choking gas made
  • SO2 + H2O → H2SO3 pH (0-2)
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9
Q

Explain why sodium oxide reacts to form an alkaline solution when added to water and state what is observed

A
  • O2– accepts a proton forming OH– ions
  • NaOH is formed
  • O2– + H2O→ 2OH– (2m)
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10
Q

How can we prove a metal oxide something has ions

A
  • heat until molten
  • if molten oxide conducts electricity its ionic
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11
Q

Why does Na2O have a high mp

A
  • Ionic lattice
  • Strong electrostatic forces of attraction between ions
  • A lot of energy needed to break the ionic forces
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12
Q

Why does SO2 have a low mp?

A
  • Simple Molecular structure
  • Weak van der Waals forces between molecules
  • Little energy needed to break them
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13
Q

Why does P4O10 have a higher mp than SO2?

A
  • P4O10 bigger molecule (Mr) than SO2
  • Both simple molecular
  • The van der Waals forces between molecules stronger
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14
Q

Structure of P4O10 and explain the low mp

A
  • simple covalent molecule (2m)
  • weak van der Waals forces between molecules
  • low energy needed to break van der Waals forces
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15
Q

Write 2 equations to show the amphoteric nature of Al

A
  • Al(OH)3 + OH-– → Al(OH)4- (acidic)
  • Al(OH)3 + 3H+ + 3H2O → Al(H2O)6 3+ (basic)

e.G

  • Al(OH)3 + NaOH ⇒ NaAl(OH)4
  • 2Al(OH)3 + 3H2SO4 ⇒ Al2(SO4)3 + 6H2O
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16
Q

Why is Al(OH)3 insoluble

A
  • ΔG is +ve for the reaction
  • Sum of the hydration enthalpies is less than that of the covalent bond energies
17
Q

Explain the pattern of conductivity of Na2O

A
  • Can’t conduct when solid as ions can’t move in a solid state
  • When molten or in solution, the ions are free to move
18
Q

Simple chemical test to show that Na2O is present

A
  • Add water, NaOH forms
  • Test pH
  • pH should be 13/14
19
Q

Why is SiO2 classed as an acidic oxide?

A

Reacts with bases, neutralising them

CaO + SiO2 →CaSiO3

20
Q

Write ionic equations to show the reaction of Cr(OH)3 with HCl and NaOH

A

Cr(OH)3 + 3H2O + 3H+ → [Cr(H2O)6] 3+

Cr(OH)3 + 2H2O + OH– → [Cr(OH)6]<span>3-</span>

21
Q

Why is the mp of Mg greater than Na

A
  • Mg2+ has a greater charge density than Na+
  • Attracts sea of electrons more strongly
  • Mg has more delocalised electrons per Mg2+ ion
  • Metallic bonding stronger

Chemistry Unit 5 (7 decks)

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