Period 3

Structure of Element for Sodium

Giant metallic

Structure of Element for Magnesium

Giant metallic

Structure of Element for Aluminium

Giant Metallic

Structure of Element for Silicon

Macromolecular

Structure of Element for Phosphorus

Molecular (P₄)

Structure of Element for Sulfur

Molecular (S₈)

Structure of Element for Chlorine

Molecular (Cl₂)

Structure of Element for Argon

Atomic

What is the trend in melting points for period 3

Giant structures such as the metals and silicon have higher melting points, increasing going across the group

Molecular structures have lower melting points, decreasing going across the group

The melting points of Sulfur, Phosphorus and chlorine are dependent on the number of electrons in each of the structures for Van Der Waals forces

S₈>P₄>Cl₂

What is the trend in atomic radii going across period 3

Atomic radius decreases as there is a similar level of shielding and an increase in nuclear charge, drawing the electrons in with greater strength

What is the tend in first ionisation energy

General trend:

Increases going across a period as the number of protons in the nucleus increases however there is a similar level of shielding

Drop between Mg and Al:

Mg loses an electron in the 3s orbital

Al loses an electron in the 3p orbital

The electron lost from the 3p orbital is in a higher energy level than the s electron therefore less energy is needed to remove it

Drop between P and S

Phosphorus has no paired electrons in the p orbital (Each p electron is in a different orbital

Sulfur has two electrons paired in a p orbital, one of these will be easier to remove than an unpaired one due to the repulsion of the other electron in the same orbital

Reaction of Magnesium with Water

Mg_(s) + 2H₂O_(l) → Mg(OH)_2(aq) + H_2(g)

Reaction of Magnesium with Water observations

• Very slow reaction at room temperature

• Only a few bubbles of hydrogen are formed

• weaker alkaline solution is formed

Reaction of Sodium with water

2Na_(s) + 2H₂O_(l) → 2NaOH_(aq) + H_2(g)

Reaction of Sodium with water observations

• Sodium floats on surface of water

• Rapid fizzing

• pH indicator will show that an alkali solution has been formed

• Sodium melts because of the heat energy released by the reaction

Reaction of Magnesium with steam

Mg_(s) + H₂O_(g) → MgO_(aq) + H_2(g)

Reaction of Magnesium with steam observations

• Bubbling

• Much more rapid than reaction with water

Reaction of Sodium with oxygen

2Na_(s) + ½O_2(g) → Na₂O_(s)

Reaction of Magnesium with oxygen

2Mg_(s) + O_2(g) → 2MgO_(s)

Reaction of Magnesium with oxygen observations

• Magnesium strip burns with bright white flame

• White powder is produced

• Flame is more intense if the burning magnesium is lowered into a gas jar of oxygen

Reaction of Aluminium with oxygen

4Al_(s) + 3O_2(g) → 2Al₂O_3(s)

Reaction of Aluminium with oxygen observations

• Burns brightly in air

• White powder (Aluminium oxide) is formed

• (Al powder is heated then lowered into a gas jar of oxygen)

Reactivity of Aluminium

Aluminium is always coated with a strongly bonded surface layer of oxide

Protects the aluminium from further reaction

As a result of this aluminium appears to be unreactive

(Used for saucepans, garage doors, window frames)

Reaction of Silicon with oxygen

Si_(s) + O_2(g) → SiO_2(s)

Reaction of Phosphorus with oxygen

4P_(s) + 5O_2(g) → P₄O_10(s)

(If oxygen is limited, phosphorus trioxide is also formed)

Reaction of Phosphorus with oxygen observations

White phosphorus:

• White smoke is given off (Phosphorus pentoxide)

Red phosphorus vs White phosphorus

Red phosphorus must be heated before it will react with oxygen

White phosphorus spontaneously reacts with air

They are allotropes of phosphorus (Same element with differently arranged atoms)

Reaction of Sulfur with oxygen

S_(s) + O_2(g) → SO_2(g)

Reaction of Sulfur with oxygen observations

When sulfur powder is heated and lowered into a gas jar of oxygen it burns with a blue flame and forms a colourless gas

Covalent Character of Aluminium oxide

Aluminium oxide is ionic but has some covalent character

Aluminium forms small ion with large positive charge.

Aluminium ion has a high charge density

The aluminium can approach the Oxygen and distort the electron cloud

Structure of the period 3 metal oxides

Sodium, magnesium and aluminium oxides all form giant ionic lattices

Aluminium oxide is ionic but has some covalent character

Melting point of the period 3 metal oxides

Sodium magnesium and aluminium oxides all have high melting points as a result of the giant ionic lattices formed, as bonding extends throughout the compound

Structure of the period 3 non-metal oxides

Silicon oxide - macromolecular structure

Phosphorus and sulfur oxides - separate covalently bonded molecules

States of matter of the period 3 non-metal oxides

Sulfur dioxide and Sulfur Trioxide are gases at 298 K

Phosphorus oxides are solids at 298 K, but have relatively low melting points as a result of their weak VDW forces and PDP-PDP forces

Reaction of Sodium oxide with water

Na₂O_(s) + H₂O_(l) → 2Na⁺_(aq) + 2OH^-_(aq)

Reaction of magnesium oxide with water

MgO_(s) + H₂O_(l) → Mg(OH)_2(s)

Which oxides are insoluble in water

Aluminium oxide and Silicon Dioxide

Reaction of phosphorus pentoxide with water equation

P₄O_10(s) + 6H₂O_(l) → 4H₃PO₄^-_(aq)

Stages of ionisation of H₃PO_4(aq)

H₃PO_4(aq) ⇌ H⁺_(aq) + H₂PO₄^-_(aq)

Reaction of phosphorus pentoxide with water is

quite violent and produces an acidic solution

Reaction of sulfur dioxide with water

SO_2(g) + H₂O_(l) → H₂SO_3(aq)

Dissociation of Sulfurous acid

H₂SO_3(aq) ⇌ H⁺_(aq) + HSO₃^-_(aq)

Reaction of sulfur trioxide with water → Further reaction by product

SO_3(g) + H₂O_(l) → H₂SO_4(aq) → H⁺_(aq) + H₂SO₄^-_(aq)

What is the general trend in pH of solutions of the oxides of the elements

from alkaline to acidic across the period

What is the acidic/basic nature of sodium oxide (+ Reaction with H₂SO₄)

• Acts as a base

• Sodium oxide + Acid → Salt + Water

• Na₂O_(s) + H₂SO_4(aq) → Na₂SO_4(aq) + H₂O_(l)

What is the acidic/basic nature of magnesium oxide (+Reaction with HCl)

• Acts as a base

• Magnesium oxide + Acid → Salt + Water

• MgO_(s) + 2HCl_(aq) → MgCl_2(aq) + H₂O_(l)

What is the acidic/basic nature of aluminium oxide

• Aluminium oxide is amphoteric (Reacts with both acids and alkalis)

• Aluminium oxide + Alkali → Salt + Water

• Aluminium oxide + Acid → Salt + Water

What is the acidic/basic nature of silicon dioxide

• Acts as a weak acid

• Reacts with strong bases

• Silicon dioxide + Strong Base → Salt + Water

What is the acidic/basic nature of phosphorus pentoxide (+ Reaction with sodium hydroxide)

• Phosphorus pentoxide reacts with water to form phosphoric (V) acid

• Reacts with a base (Such as sodium hydroxide) in three stages

Reaction of Phosphoric acid with Sodium hydroxide

• H₃PO_4(aq) + NaOH_(aq) → NaH₂PO_4(aq) + H₂O_(l)

• NaH₂PO_4(aq) + NaOH_(aq) → Na₂HPO_4(aq) + H₂O_(l)

• Na₂HPO_4(aq) + NaOH_(aq) → Na₃PO_4(aq) + H₂O_(l)

Overall Equation:

H₃PO_4(aq) + 3NaOH_(aq) → Na₃PO_4(aq) + 3H₂O_(l)

What is the acidic/basic nature of sulfur dioxide (Reaction with sodium hydroxide)

Initial reaction:

SO_2(aq) + NaOH_(aq) → NaHSO_3(aq)

(Product is called sodium hydrogensulfate (IV))

Reaction is followed by:

NaHSO_3(aq) + NaOH_(aq) → Na₂SO_3(aq) + H₂O_(l)

(Product is called sodium sulfate (IV))