Topic 2.4 - Properties of Period 3 Elements and their Oxides

Appearance and physical properties of sodium?

Metallic, shiny, conducts electricity (worst conductor out of the metals)

Reaction of sodium with acid?

Na + acid → H2 + salt

Reaction of sodium with cold water - equation and observations?

Vigorous reaction, floats on water, fizzes, melts due to -ΔH of the reaction.

NaOH is pH 13-14.

2Na + 2H2 O → 2NaOH + H2

Reaction of sodium with oxygen (equation and observations)?

Bright yellow flame, forms white powder of Na2 O 2Na + ½ O2 → Na2 O

Appearance and physical properties of magnesium?

Metallic, shiny, conducts electricity (between Na and Al in terms of how well it does)

Reaction of Mg with cold water (observations and equation)?

Very slow reaction.

pH = 10 as Mg(OH)2 is sparingly soluble

Mg + 2H2 O → H2 + Mg(OH)

Reaction of Mg with steam (observations and equation)?

Much faster. Mg + H2 O → MgO + H2

Reaction of Mg with oxygen (observations and equation)?

Bright white flame, forms white powder of MgO

2Mg + O2 → 2MgO

Appearance and physical properties of aluminium?

Metallic, shiny, best conductor of electricity in period 3

Reaction of Al with cold water?

No reaction

Reaction of Al with oxygen (equation and observations)?

Heat and lower into jar of O2 → bright flame, forms white powder.

4Al + 3O2 → 2Al2 O3

Why is aluminium considered unreactive even though the metal itself is reactive?

Covered by Al2 O3 from where oxygen has oxidised the surface of the Al.

Al2 O3 is unreactive.

Makes it useful for saucepans, window frames etc.

If Al2 O3 is scratched off, Al reacts rapidly with air to form a new coat

Appearance and physical properties of silicon?

Semimetal (metalloid), semiconductor (conducts electricity to an extent and in certain conditions)

Reaction of silicon with oxygen (observations and equation)?

Heat strongly

Si + O2 → SiO2 (white powder)

Appearance and physical properties of phosphorus?

Non-metal, low m.p. And b.p., does not conduct electricity.

Red Phosphorus as a crystal structure

White Phosphorus as P4

Reaction of phosphorous in excess oxygen (observations and equation)?

Red P needs to be heated significantly first, white P ignites spontaneously in air

Phosphorus pentoxide (white crystalline solid) formed

4P + 5O2 → P4 O10

Reaction of phosphorous in limited oxygen (observations and equation)?

Incomplete combustion: colourless liquid phosphorus trioxide is formed

. 4P + 3O2 → P4 O6

Appearance and physical properties of sulfur?

Non-metal, low mp and bp, does not conduct electricity

Reaction of sulfur with oxygen (observations and equation)?

Need to heat and lower into a jar of oxygen

. Colourless gas sulfur dioxide formed.

Some SO3 also formed

. S + O2 → SO2

What are the different types of structure and bonding displayed by the period 3 oxides?

• Na ionic lattice

• Mg ionic lattice

• Al ionic lattice with covalent character;

Al3 + distorts O2- electron cloud

• Si giant covalent

• P simple molecular covalent

• S simple molecular covalent

What is the trend in melting points for period 3 oxides (state highest and lowest and why and draw graph)?

Highest is MgO, lowest is SO2 ; increases along group for metals for Na2 O and MgO due to stronger ionic bonding, but Al2 O3 is lower due to the covalent character of the bonding. Decreases with size for simple molecular molecules.

Which period 3 oxides are basic?

Na2 O and MgO

Reaction of Na oxide with water? pH?

Na2 O + H2 O → 2Na+ + 2OH-;

pH = 14

Reaction of Mg oxide with water? pH?

MgO + H2 O → Mg2+ + 2OH- ⇌ Mg(OH)2

pH = 9-10 as Mg(OH)2 is sparingly soluble

What are the products if Na2 O and MgO are reacted with acid?

Salt and water only

Is aluminium oxide acidic or basic?

It is amphoteric; can act as either an acid or a base

Is aluminium oxide soluble?

Not in water

Reaction of aluminium oxide with HCl?

Al2 O3 + 6HCl → 3H2 O + 2AlCl3

Reaction of aluminium oxide with NaOH?

Al2 O3 + 2NaOH + 3H2 O → 2NaAl(OH)4 ;

sodium aluminate is formed

Is silicon dioxide soluble in water?

No

In what conditions will silicon dioxide act as an acid?

Reacts as a weak acid with a strong base (e.g. hot, conc NaOH)

Reaction of silicon dioxide with hot, conc NaOH?

SiO2 + 2NaOH → H2 O + Na2 SiO3 - sodium silicate

How is silicon dioxide used in the production of Fe?

SiO2 + CaO → CaSiO3 - calcium silicate

Reaction of Phosphorus pentoxide with water? pH?

P4 O10 + 6H2 O → 4H3 PO4 ;

pH = 1-2

Dissociation of the acid formed (H3 PO4 )?

H3 PO4 → H+ + H2 PO4-

Reaction of P4 O10 with NaOH?

3NaOH + H3 PO4 → Na3 PO4 + 3H2 O

Reaction of SO2 with water? pH?

SO2 + H2 O → H2 SO3 ;

weak acid → pH = 2-3

Reaction of SO3 with water? pH?

SO3 + H2 O → H2 SO4

strong acid → pH = 0-1

Reaction of SO2 with NaOH? (2 stages)

SO2 + NaOH → NaHSO3

NaHSO3 + NaOH → Na2 SO3 + H2 O

How can flue gases be removed by CaO?

CaO + SO2 → CaSO3 (calcium sulfite)

Draw the structure of H3 PO4 ?

How many electrons does P have in its outer shell in H3 PO4 ?

10

What is the shape and bonding in PO4 3-?

Electrons delocalise to give tetrahedral structure with 109.5o bond angle.

Each P-O bond is the same length

Draw the structure and bonding of H2 SO4 ?

What is the structure, bonding and shape of SO4 2-?

Electrons delocalise → tetrahedral with 109.5o bond angle.

Each S-O bond is the same

What is the structure, bonding and shape of SO3 2-?

Bond angle = 106o (trigonal pyramid shape), each S-O bond is the same,

S has one lone pair of electrons.

Uses of MgO?

Additive for cattle feed

How useful is Al2 O3 ?

Oxide layer on Aluminium makes it very useful as it is unreactive and returns quickly if it is scratched off

Uses of SO2 ?

Reactant in contact process (making H2 SO4 )

Would Lithium oxide or sodium oxide have a higher melting point? Why?

Li2 O has a higher m.p. , since Li+ is a smaller ion than Na+, so the O2- and Li+ charge centres are closer together and there is a greater electrostatic force of attraction between the oppositely charged ions.