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 → H 2 + 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 + 2H 2

O → 2NaOH + H 2

Reaction of sodium with

oxygen (equation and

observations)?

Bright yellow flame, forms white powder of Na 2

O

2Na + ½ O 2 → Na 2

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 + 2H 2

O → H 2 + Mg(OH) 2

Reaction of Mg with steam

(observations and

equation)?

Much faster.

Mg + H 2 O → MgO + H 2

Reaction of Mg with oxygen

(observations and

equation)?

Bright white flame, forms white powder of MgO

2Mg + O 2 → 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 O 2 → bright flame,

forms white powder.

4Al + 3O 2 → 2Al 2

O 3

Why is aluminium

considered unreactive even

though the metal itself is

reactive?

Covered by Al 2 O 3 from where oxygen has oxidised the

surface of the Al. Al 2 O 3 is unreactive. Makes it useful for

saucepans, window frames etc.

If Al 2 O 3 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 + O 2 → SiO 2 (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 P 4

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 + 5O 2 → P 4

O 10

Reaction of phosphorous in

limited oxygen

(observations and

equation)?

Incomplete combustion: colourless liquid

phosphorus trioxide is formed.

4P + 3O 2 → P 4

O 6

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 SO 3

also formed.

S + O 2 → SO

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; Al 3

+ distorts O 2

- 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 SO 2 ;

increases along group for metals for

Na 2 O and MgO due to stronger ionic

bonding, but Al 2 O 3 is lower due to the

covalent character of the bonding.

Decreases with size for simple

molecular molecules

Which period 3 oxides are

basic?

Na2O and MgO

Reaction of Na oxide with

water? pH?

Na2O + H2O → 2Na+ + 2OH-

pH = 14

Reaction of Mg oxide with

water? pH?

MgO + H2O → Mg2+ + 2OH- ⇌ Mg(OH)2 pH = 9-10 as Mg(OH)2 is sparingly soluble

What are the products if

Na 2 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 water

Reaction of aluminium oxide

with HCl?

Al2O3 + 6HCl → 3H2O + 2AlCl3

Reaction of aluminium oxide

with NaOH?

Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4 ; sodium aluminate is formed

Is silicon dioxide soluble in

water?

No

In what conditions will

silicon dioxide act as an

acid?

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 → H2O + Na2SiO3 - sodium silicate

How is silicon dioxide used

in the production of Fe?

SiO 2 + CaO → CaSiO 3 - calcium silicate

Reaction of Phosphorus

pentoxide with water? pH?

P4O10 + 6H2O → 4H3PO4 ; pH = 1-2

Dissociation of the acid

formed (H 3 PO 4 )?

H 3 PO 4 → H + + H 2 PO 4

-

Reaction of P 4 O 10 with

NaOH?

3NaOH + H 3 PO 4 → Na 3 PO 4 + 3H 2 O

Reaction of SO 2 with water?

pH?

SO 2 + H 2

O → H 2

SO 3 ; weak acid → pH = 2-3

Reaction of SO 3 with water?

pH?

SO 3 + H 2 O → H 2 SO 4

strong acid → pH = 0-1

Reaction of SO 2 with

NaOH? (2 stages)

SO 2 + NaOH → NaHSO 3

NaHSO 3 + NaOH → Na 2 SO 3 + H 2 O

How can flue gases be

removed by CaO?

CaO + SO 2 → CaSO 3 (calcium sulfite)

Draw the structure of

H 3 PO 4 ?

How many electrons does P

have in its outer shell in

H 3 PO 4 ?

10

What is the shape and

bonding in PO 4

3- ?

Electrons delocalise to give tetrahedral structure

with 109.5 o bond angle. Each P-O bond is the

same length

Draw the structure and

bonding of H 2 SO 4 ?

What is the structure,

bonding and shape of

SO 4

2- ?

Electrons delocalise → tetrahedral with 109.5 o

bond angle. Each S-O bond is the same

What is the structure,

bonding and shape of

SO 3

2- ?

Bond angle = 106 o (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 Al 2 O 3 ?

Oxide layer on Aluminium makes it very useful as

it is unreactive and returns quickly if it is

scratched off

Uses of SO 2 ?

Reactant in contact process (making H 2

SO 4

)

Would Lithium oxide or

sodium oxide have a higher

melting point? Why?

Li 2

O has a higher m.p., since Li + is a smaller ion

than Na + , so the O 2- and Li + charge centres are

closer together and there is a greater

electrostatic force of attraction between the

oppositely charged ions.