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Chemistry: CHEM 5 > Periodicity > Flashcards

Periodicity Flashcards

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1
Q

What are the features of sodium, magnesium and aluminium?

A

Giant metallic structure:

  • Metallic bonding
  • Shiny, conduct electricity, and react with dilute acids to give hydrogen and salts.
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2
Q

What are the features of silicon?

A

Macromolecule/giant covalent structure:

  • Semi-metal (covalent bonding with ionic character)
  • Conducts electricity to some extent (useful for semiconductor devices.
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3
Q

What are the features of phosphorus, sulphur and chlorine?

A

Molecular structure (P4, S8, Cl2)

  • Non-metals, covalent bonding
  • Do not conduct electricity, have low melting and boiling points.
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4
Q

What are the features of argon?

A

Noble gas

  • Atomic
  • Chemically unreactive, exists as separate atoms.
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5
Q

What is the trend in melting points of the elements of period 3?

A
  • Increases from Na  Al, due to increased metallic bond strength (more electrons in sea, with larger charge on smaller ion)
  • Large increase in melting point for silicon, due to the giant macromolecular structure.
  • Decrease, increase, decrease (P, S, Cl); S8 > P4 > Cl2, larger van der Waals due to more electrons.
  • Decrease for argon, due to it being a noble gas and a monatomic species.
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6
Q

What is the trend in atomic radius of the elements of period 3?

A

Decreases across the period

  • Increased charge pulls electrons closer to the nucleus.
  • No additional electron shells to provide more shielding
  • Nuclear force of attraction is stronger, meaning the radius is smaller.
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7
Q

What is the trend in ionisation energy of the elements of period 3?

A

First IE increases across the period.

  • As you go across, atomic radius decreases, electrons are held more strongly, due to increased charge but no extra shielding.
  • Due to the electron being held more strongly, it gets increasingly difficult to remove the electron.
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8
Q

Which elements of period 3 react with water?

A
  • Metals: Sodium and Magnesium

- Non-metals: Chlorine (chlorination)

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9
Q

Sodium with water

A

-Vigorous reaction, sodium floats on the surface of the water and fizzes rapidly, melting because of the heat given out from the reaction:
2Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)

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10
Q

Magnesium with water

A

-Very slow at room temperature, only a few bubbles of hydrogen.
-A less alkaline solution is formed than with sodium because magnesium hydroxide is sparingly soluble.
Mg(s) + 2H2O(l) –> Mg(OH)2(aq) + H2(g)

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11
Q

Heated magnesium and steam

A

-The reaction of magnesium and water is much faster if Mg is heated and steam is used
Mg(s) + H2O(g) –> MgO(s) +H2(g)

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12
Q

Which elements of period 3 react with oxygen?

A

All elements in period 3 (except argon) are relatively reactive. Their oxides can be prepared by direct reaction of the element with oxygen.
-All reactions are exothermic.

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13
Q

Sodium with oxygen

A

-Vigorous reaction, burns brightly in air with a yellow/orange flame.
2Na(s) + 0.5O2(g) –> 2Na2O(s)

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14
Q

Magnesium with oxygen

A

-Vigorous reaction, burns in air with a bright white flame, forms white powder.
-More intense flame if lowered into a gas jar of oxygen
2Mg(s) + O2(g) –> 2MgO(s)

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15
Q

Aluminium with oxygen

A

-Slow reaction (useful for saucepans, garage doors etc). When lowered into a gas jar of oxygen, it burns brightly with white sparks, forms white powder.
-Although aluminium is a reactive metal, it is always coated with a strongly bonded surface layer of oxide – this protects it from further reaction. Even if scratched off, the exposed Al reacts rapidly and seals the surface.
4Al(s) + 3O2(g) –> 2Al2O3(s)

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16
Q

Silicon with oxygen

A

-Slow reactions, must be heated strongly in oxygen.

Si(s) + O2(g) –> SiO2(s)

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17
Q

Phosphorus with oxygen

A

-Red phosphorus must be heated before it will react with oxygen.
-White phosphorus spontaneously ignites in air and the white smoke of phosphorus pentoxide is observed (it is kept in water to prevent this).
4P(s) + 5O2(g) –> P4O10(s)
-If oxygen supply is limited, phosphorus trioxide, P2O3, is also formed.

18
Q

Sulfur with oxygen

A

-Burns steadily, when lowered into a gas jar of oxygen (powder), burns with a blue flame to form colourless sulphur dioxide.
S(s) + O2(g) –> SO2(g)

19
Q

What is the trend in melting point of the oxides of elements in period 3?

A
  • Increase between Na2O and MgO.

- Decrease after MgO.

20
Q

Why do the metal oxides of period 3 have high melting points?

A

Sodium, magnesium and aluminium oxides all form giant ionic lattices where the bonding extends throughout the compound. This results in high melting points.

21
Q

Why does MgO have a higher melting point than Na2O?

A

MgO has a higher melting point than Na2O because magnesium forms 2+ ions which attract O2- ions more strongly than the 1+ sodium ions in Na2O. This means more energy is required to break this stronger attraction.

22
Q

Why does Al2O3 have a lower melting point than MgO?

A

Al2O3 has a lower melting point than MgO (unexpectedly). This is because the 3+ ions distort the oxygen’s electron cloud, making the bonds partially covalent, and therefore a lower melting point than pure ionic compounds with very high melting points.

23
Q

Why does SiO2 have a higher melting point than the rest of the non-metals?

A

SiO2 has a higher melting point than other non-metal oxides because it has a giant macromolecular structure. Strong covalent bonds hold the structure together, so a lot of energy is needed to break the bonds.

24
Q

Why do P4O10 and SO2 have low melting points?

A

P4O10 and SO2 are covalent molecules. They have relatively low melting points because they form simple molecular structures, held together by weak intermolecular forces (dipole-dipole and van der Waals), which take little energy to overcome.

25
Q

What is the general trend of the reactions of period 3 oxides with water?

A
  • Metal oxides (left of period) form alkaline solutions.
  • Non-metal oxides (right of period) form acidic solutions
  • Those in the middle of period do not react.
26
Q

Sodium oxide with water

A

-Basic oxide
-Reacts to give sodium hydroxide (strongly alkaline)
-pH = 13-14
Na2O(s) + H2O(l) –> 2Na+(aq) + 2OH-(aq) (+2NaOH)

27
Q

Magnesium oxide with water

A

-Basic oxide
-reacts to give magnesium hydroxide, sparingly soluble (somewhat alkaline)
-pH = 10
MgO(s) + H2O(l) –> Mg(OH)2(s) –> Mg2+(aq) + 2OH-(aq)

28
Q

Why do sodium and magnesium oxides form alkaline solutions?

A

Na and Mg oxides are composed of ions, both of which contain the oxide ion (O2-), a very strong base (strongly attracts protons). It readily reacts with water to produce hydroxide ions, forming an alkaline solution.
-MgO is less soluble than Na2O, so it produces a less alkaline solution.

29
Q

Which oxides of period 3 elements do not react with water?

A

Insoluble oxides (pH = 7)

  • Aluminium oxide
  • Silicon dioxide
30
Q

Why doesn’t aluminium oxide react with water?

A

Aluminium oxide is ionic but the bonding is too strong to be separated, due to additional covalent bonding, it is insoluble.

31
Q

Why doesn’t silicon dioxide react with water?

A

-It is a giant macromolecule and water will not affect this type of structure, it is insoluble.

32
Q

Phosphorus pentoxide and water

A

-Acidic oxide
-Reacts violently to produce an acidic solution of phosphoric(v) acid.
P4O10(s) + 6H2O(l) –> 4H3PO4(aq)
This ionises so the solution is acidic (fairly strong):
H3PO4(aq) –> H+(aq) + H2PO4-(aq)
-pH = 1-2

33
Q

Sulfur dioxide and water

A

-Acidic oxide
-Fairly soluble in water, reacts to give an acidic solution of sulfuric(IV) acid (sulfurous acid)
SO2(g) +H2O(l) –> H2SO3(aq)
-This partially dissociates producing H+ ions, causing acidity
H2SO3(aq) –> H+(aq) + HSO3-(aq)
-pH = 2-3

34
Q

Sulfur trioxide and water

A

-Acidic oxide
-Reacts violently with water to produce sulfuric(VI) acid.
So3(g) + H2O(l) –> H2SO4(aq) –> H+(aq) + HSO4-(aq)
-pH = 0-1

35
Q

Why do phosphorus and sulfur oxides react with water?

A

P4O10 and SO2/SO3 are covalent molecules and react to form acidic solutions.

36
Q

How do sodium and magnesium oxides react with acids and bases?

A

Sodium and magnesium oxides are basic oxides and so only react with acids to give salt and water.
Na2O(s) + H2SO4(aq) –> Na2SO4(aq) + H20(l)
MgO(s) + 2HCl(aq) –> MgCl2(aq) + H20(l)

37
Q

How does aluminium oxide react with acids and bases?

A

Al2O3 is amphoteric, meaning it can react with acids and bases
Al2O3(s) + 6HCl(aq) –> 2AlCl3(aq) + 3H20(l)
Al2O3(s) + 2NaOH(aq) + 3H2O(l) –> 2NaAl(OH)4(aq) (NaOH must be hot and concentrated).

38
Q

How does silicon dioxide react with acids and bases?

A

SiO2 will react with strong bases, as a weak acid.

SiO2(s) + 2NaOH(aq) –> Na2SiO3(aq) + H2O(l) (NaOH must be hot and concentrated).

39
Q

How does phosphorus pentoxide react with acids and bases?

A

-Reacts with alkali (basically the reaction of phosphoric(V) acid, as this is formed when P4O10 reacts with water. It has 3 –OH groups, each with an acidic hydrogen atom, so it reacts in 3 stages. Each time a hydrogen is replaced by a sodium atom.
H3PO4(aq) + NaOH(aq) –> NaH2PO4(aq) + H2O(l)
NaH2Po4(aq) + NaOH(aq) –> Na2HPO4(aq) + H2O(l)
Na2HPO4(aq) + NaOH(aq) –> Na3PO4(aq) + H2O(l)
-Overall:
3NaOH(aq) + H3PO4(aq) –> Na3PO4(aq) + 3H2O(l)

40
Q

How does sulfur dioxide react with acids and bases?

A

-If we add NaOH to an aqueous solution of sulfur dioxide, we first form sodium hydrogensulfate(IV):
SO2(aq) + NaOH(aq) –>NaHSO3(aq)
-Followed by sodium sulfate(IV):
NaHSO3(aq) + NaOH(aq) –>Na2SO3(aq) + H2O(l)

Chemistry: CHEM 5 (6 decks)

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