Inorganic 4: Period 3

Question 1

Describe properties of sodium.

Answer 1

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

Question 2

Describe properties of magnesium.

Answer 2

Alkali earth metal
Light and strong
Used in alloy wheels

Question 3

Describe properties of aluminium.

Answer 3

Metal
Poor conductor
Lightweight

Question 4

Describe properties of silicon.

Answer 4

Metalloid
Semi-conductor
Used in computer chips

Question 5

Describe properties of phosphorous.

Answer 5

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

Question 6

Describe properties of sulfur.

Answer 6

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

Question 7

Describe properties of chlorine.

Answer 7

Non-metal halogen
Highly reactive
Toxic gas
Diatomic

Question 8

Describe properties of argon.

Answer 8

Noble gas
Monatomic
Colourless and inert
Poor conductor

Question 9

Describe the general trend in melting points across period 3.

Answer 9

Question 10

Why does the melting point increase from sodium to aluminium?

Answer 10

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

Question 11

Why is the melting point of silicon so high?

Answer 11

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

Question 12

Why does sulfur have a higher melting point than phosphorous?

Answer 12

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.

Question 13

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

Answer 13

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

Question 14

Describe sodium oxide.

Answer 14

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

Question 15

Describe magnesium oxide.

Answer 15

Giant ionic lattice
Forms Mg(OH)2 in water

Question 16

Describe aluminium oxide.

Answer 16

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

Question 17

Define amphoteric.

Answer 17

Reacts with both acids and alkalis

Question 18

Describe silicon dioxide.

Answer 18

Giant covalent lattice
Completely insoluble

Question 19

Describe phosphorous oxide.

Answer 19

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

Question 20

Describe sulfur dioxide.

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Exothermic

Question 26

Describe how sodium reacts with oxygen and give the equation.

Answer 26

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

Question 27

Describe how magnesium reacts with oxygen and give the equation.

Answer 27

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

Question 28

Describe how aluminium reacts with oxygen and give the equation.

Answer 28

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

Question 29

Describe how silicon reacts with oxygen and give the equation.

Answer 29

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

Question 30

Describe how phosphorous reacts with oxygen and give the equation.

Answer 30

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

Question 31

Describe how sulfur reacts with oxygen and give the equation.

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

Why is the melting point of silicon dioxide so high?

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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

Question 37

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

Answer 37

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)

Question 38

Describe how aluminium oxide reacts with water.

Answer 38

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

Question 39

Describe how silicon dioxide reacts with water.

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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

Question 43

Describe how phosphorous oxide (P4O10) reacts with water.

Answer 43

Reacts violently P4O10 + 6H2O --> 4H3PO4

Question 44

Describe how sulfur dioxide (SO2) reacts with water.

Answer 44

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

Question 45

Describe how sulfur trioxide (SO3) reacts with water.

Answer 45

Reacts violently SO3 + H2O --> H2SO4

Question 46

Why does aluminium oxide have some covalent character?

Answer 46

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

Question 47

What is covalent character?

Answer 47

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)