Inorganic 4: Period 3 Flashcards by Aoife Harkin

Describe properties of sodium.

Alkali metal
Highly reactive
Forms NaO when exposed to air
Forms a giant metallic lattice
Strong electrostatic FOAs with delocalised electrons and positive ions
Good conductor of heat and electricity

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Describe properties of magnesium.

Alkali earth metal
Light and strong
Used in alloy wheels

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Describe properties of aluminium.

Metal
Poor conductor
Lightweight

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Describe properties of silicon.

Metalloid
Semi-conductor
Used in computer chips

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Describe properties of phosphorous.

Non-metal
Forms phosphate compounds
Found as P4(s) at room temperature

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Describe properties of sulfur.

Non-metal
Bright yellow solid at room temperature
Found as S8

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Describe properties of chlorine.

Non-metal halogen
Highly reactive
Toxic gas
Diatomic

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Describe properties of argon.

Noble gas
Monatomic
Colourless and inert
Poor conductor

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Describe the general trend in melting points across period 3.

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Why does the melting point increase from sodium to aluminium?

Charge on the ion increases.
Stronger electrostatic forces of attraction.
Smaller ionic radius.
Higher charge density.

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Why is the melting point of silicon so high?

Silicon forms a giant covalent lattice.
Very high melting point due to many strong covalent bonds.
Require more energy to break.

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Why does sulfur have a higher melting point than phosphorous?

Sulfur is found naturally as S8, whereas phosphorous is found as P4.
So sulfur has more electrons and much stronger van Der Waal forces of attraction.

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Why are the melting points of chlorine and argon lower than sulfur?

Because they have less weaker van Der Waal forces of attraction due to less electrons.
Less energy needed to overcome forces.

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Describe sodium oxide.

Na2O
Giant ionic lattice
Forms NaOH in water
Completely dissolves
Basic oxide

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Describe magnesium oxide.

Giant ionic lattice
Forms Mg(OH)2 in water

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Describe aluminium oxide.

Strongest giant ionic lattice
Some covalent character
Amphoteric (reacts with both acids and alkalis)
Completely insoluble in water

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Define amphoteric.

Reacts with both acids and alkalis

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Describe silicon dioxide.

Giant covalent lattice
Completely insoluble

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Describe phosphorous oxide.

Simple covalent molecule
Forms phosphoric acid (triprotic) in water
Strong van der Waals due to lots of electrons

Describe sulfur dioxide.

Basic oxide
Simple covalent molecule
Weak van der Waal and dipole-dipole forces of attraction
Bent, 117 bond angle
Forms sulphuric acid in water

Describe the reaction of sodium with water and give the equation.

Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)
Reacts vigorously
Floats on the surface and fizzes rapidly
Melts due to heat released in reaction
Strongly alkaline NaOH formed

Describe the reaction of magnesium with water and give the equation.

Mg(s) + H2O(l) –> Mg(OH)2(aq) + H2(g)
Very slow
Only a few bubbles of hydrogen form

Describe the reaction of magnesium with steam and give the equation.

Mg(s) + 2H2O(g) –> MgO(s) + H2(g)
Much faster
Gives off MgO and hydrogen gas

Describe the reaction of chlorine with water and give the equation.

Cl2(g) + H2O(g) –> HCl + HClO
Disproportionation
Dissolves giving very pale green solution

Are the reactions of period 3 elements with oxygen exothermic or endothermic?

Exothermic

Describe how sodium reacts with oxygen and give the equation.

2Na(s) + 1/2 O2(g) --> Na2O(s) Burns with bright yellow flame White powder

Describe how magnesium reacts with oxygen and give the equation.

2Mg(s) + O2(g) --> 2MgO(s) Burns with white flame White powder

Describe how aluminium reacts with oxygen and give the equation.

4Al(s) + 3O2(g) --> 2Al2O3(s) Burns with white flame White powder

Describe how silicon reacts with oxygen and give the equation.

Si(s) + O2(g) --> SiO2(s) Burns with white flame White powder

Describe how phosphorous reacts with oxygen and give the equation.

P4(s) + 5O2(g) --> P4O10(s) Very bright white flame White powder

Describe how sulfur reacts with oxygen and give the equation.

S(s) + O2(g) --> SO2(g) Burns with blue flame Releases choking gas (sulfur dioxide) *S(s) + 1/2O2(g) --> SO3(g)

Why is the melting point of magnesium oxide higher than that of sodium oxide?

Mg2+ ions are smaller and have a higher charge than Na+.

Why is the melting point of aluminium oxide lower than magnesium oxide?

Al2O3 shows some covalent character because the Al3+ ions are highly charge dense, so polarise the oxide ions so that they can share electrons, so the ions are not perfectly spherical, the additional covalent character adds further strength to the lattice so means that more heat energy is required to overcome the bonds

Why is the melting point of silicon dioxide so high?

Giant covalent (macromolecular structure) Many strong covalent bonds Lots of energy needed to break them

Why does melting point decrease from phosphorous oxide to sulfur dioxide?

Decrease in intermolecular forces as the molecules get smaller. P4O10 > SO3 > SO2

Describe how sodium oxide reacts with water and give an equation.

Na2O(s) + H2O(l) --> 2NaOH (aq) Dissolves and then reacts with water Forms solution of pH14 (very strong alkali)

Describe how magnesium oxide reacts with water and give an equation.

MgO(s) + H2O(l) --> Mg(OH)2(aq) Some dissolves then reacts with water MgO is less soluble than Na2O due to higher lattice enthalpy Forms weak alkali (pH10)

Describe how aluminium oxide reacts with water.

No reaction. Aluminium oxide is insoluble due to very high lattice enthalpy.

Describe how silicon dioxide reacts with water.

No reaction. Silicon dioxide is a very strong macromolecular structure with many strong covalent bonds. Very high lattice enthalpy.

Describe how phosphorous oxide reacts with water and give an equation.

P4O10(s) + 6H2O(l) --> 4H3PO4(aq) Reacts violently Very strong acid (pH0)

Describe how sulfur dioxide reacts with water and give an equation.

SO2(g) + H2O(l) --> H2SO3(aq) Dissolves then reacts with water. Forms weaker acid (pH3)

Describe how sulfur trioxide reacts with water and give an equation.

SO3(g) + H2O(l) --> H2SO4(aq) Reacts violently. Very strong acid (pH0)

Describe how phosphorous oxide (P4O10) reacts with water.

Reacts violently P4O10 + 6H2O --> 4H3PO4

Describe how sulfur dioxide (SO2) reacts with water.

Dissolves and then reacts with water to form solution SO2 + H2O --> H2SO3

Describe how sulfur trioxide (SO3) reacts with water.

Reacts violently SO3 + H2O --> H2SO4

Why does aluminium oxide have some covalent character?

Because the difference in electronegativity between Al and O isn't as large as it is between Mg and O, so the O2- ions in Al2O3 can't attract the electrons in the metal-oxygen bond as strongly

What is covalent character?

Occurs in ionic bonds when the cation is highly charge dense (i.e. high charge, small ion) So the anion can be polarised, so electrons are shared between the two ions (as in a covalent bond)