Periodic Table: Chemical periodicity

Describe the trend in atomic radius across period 3

Atomic radius decreases

Explain the trend in atomic radius across period 3

* Nuclear charge increases
* Number of electrons in the outer shell increase
* Shielding remains the same
* Nuclear attraction increases so shells are more attracted to nucleus so atomic radius decreases

Describe and explain the trend in ionic radius from Na+ to Al3+

Ionic radius decreases because number of electrons decrease leading to greater attraction to the nucleus so electrons are drawn inwards

Describe and explain the trend in ionic radius from P3- to Cl-

Ionic radius increases because number of electrons increase so nuclear attraction is weaker so electrons aren’t strongly drawn inwards

Describe the trend in melting point across period 3

* From sodium to silicon: increases
* Between silicon to phosphorus: sharp decrease
* Between phosphorus to sulfur: slight increase
* From sulfur to argon: decreases

Why does melting point increase from sodium to silicon?

Atomic radius in decreases as you go across, this leads to greater electrostatic attraction so more energy is required to overcome them

Silicon has giant lattice structure which has strong covalent bonds so a lot of energy is needed to break them

Why is there a sharp decrease in melting point between silicon and phosphorus?

* Silicon has a giant covalent lattice structure and phosphorus has a simple covalent structure
* The bonds in silicon require a lot of energy to overcome
* The weak London forces between phosphorus require little energy to overcome

Why does the melting point decrease from sulfur to argon?

From sulfur to argon the molecules are getting smaller so there are weaker intermolecular forces of attraction between molecules resulting in less energy being required to overcome them

Describe and explain how electric conductivity varies across period 3

Conductivity increases from sodium to magnesium to aluminium because they have metallic bonding this means that they contain delocalised electrons that are free to move

How does ionisation energy vary across period 3?

Ionisation energy increases because nuclear charge and shielding remains the same

Nuclear attraction also increases so more energy is required to remove an electron

Describe how sodium reacts with oxygen

2Na + 1/2O2 → Na2O

Sodium burns is oxygen with an orange flame and produce sodium oxide, a white solid

Describe how magnesium reacts with oxygen

Mg + 1/2O2 → MgO

Magnesium burns in oxygen with an intense white flame to form the white solid, magnesium oxide

Describe how aluminium reacts with oxygen

4Al + 3O2 → 2Al2O3

Aluminium will burn in oxygen if powdered. White sparkles are formed and aluminum oxide, a white solid

Describe how phosphorus reacts with oxygen

P4 + 5O2 → P4O10

Phosphorus catches on fire and burns spontaneously in air with a white flame

In excess oxygen phosphorus (v) oxide is formed

Describe how sulfur reacts with oxygen

S + O2 → SO2

Sulfur burns in are with gentle heating with a pale blue flame and colourless SO2 gas is formed

Describe how sodium reacts with chlorine

2Na + Cl​2​ → 2NaCl

Burns in chlorine with a ​ bright orange flame ​ to form sodium chloride (white solid)

Describe how magnesium reacts with chlorine

Mg + Cl​2​ → MgCl​2

Burns in chlorine with a ​ bright white flame​ to form magnesium chloride (white solid)

Describe how aluminium reacts with chlorine

2Al + 3Cl​2​ → 2AlCl​3

Aluminium​ burns in a stream of chlorine to produce ​pale yellow aluminium chloride

Describe how silicon reacts with chlorine

Si + 2Cl​2​ → SiCl​4

If ​chlorine​ is passed over silicon powder, a ​colourless liquid​ forms (silicon tetrachloride)

Describe how phosphorus reacts with chlorine

P​4​ + 10Cl​2​ → 4PCl​5

White phosphorus​ burns ​ spontaneously​ in chlorine to produce phosphorus(V) chloride (off-white solid)

Describe how sodium reacts with cold water

2Na + 2H​2​O → 2NaOH + H​2

A very ​exothermic​ reaction forms hydrogen gas and a colourless solution of sodium hydroxide

Describe how magnesium reacts with cold water

Mg + H​2​O → Mg(OH)​2​ + H​2

Magnesium hydroxide forms on the outside of the metal strip

Hydrogen bubbles float to the surface of the container on the reaction stops since there is a thin layer of magnesium hydroxide on the metal

Describe how magnesium reacts with steam

Mg + H​2​O → MgO + H2

Burns with a ​bright white flame​ to produce white magnesium oxide and hydrogen

How do period 3 oxides (from sodium to sulfur) vary in oxidation number

The general trend is that oxidation number increases (except SO2) across period 3 oxides

Describe how period 3 chlorides (from sodium to phosphorus) vary in oxidation number

Oxidation number increases

Why does the oxidation number of period 3 oxides and chlorides vary?

Each element has a different number of electrons in its outer shell so each element needs to either gain, lose or share a different number of electrons to have a full outer shell and form the chloride/oxide

Describe how sodium oxide reacts with water

* Na​2​O + H​2​O → 2NaOH \n Exothermic
* Forms highly alkaline solution

Describe how magnesium oxide reacts with water

* MgO + H​2​O → Mg(OH)​2 \n Forms slightly alkaline solution
* Most of the Mg(OH)2 is insoluble and doesn’t dissolve in solution to increase pH

Describe how phosphorus (V) oxide reacts with water

P​4​O​10​ + 6H​2​O → 4H​3​PO​4

* Forms an acidic solution
* Reacts violently

Describe how sulfur dioxide reacts with water

SO​2​ + H​2​O → H​2​SO​3

* Forms an acidic solution

Describe how sulfur trioxide reacts with water

SO​3​ + H​2​O → H​2​SO​4

* Forms an acidic solution
* Reacts violently

Which two oxides do not react with water?

Aluminium and silicon

How does sodium oxide react with hydrochloric acid?

Na​2​O + 2HCl → 2NaCl + H​2​O

A ​strong base which reacts with acid to form a salt and water

How doe magnesium oxide react with hydrochloric acid?

MgO + HCl → MgCl​2​ + H​2​O

It is a weaker base than Na2O that​ reacts with warm dilute hydrochloric acid to form a salt and water

How does phosphorus (V) oxide react with NaOH?

It can form a ​range of salts​ when reacted with a base

P​4​O​10​ + 12NaOH →4Na​3​PO​4​ + 6H​2​O

How does sulfur dioxide react with NaOH?

When bubbled through sodium hydroxide: SO​2​ + NaOH → Na​2​SO​3​ + H​2​O

If sulfur dioxide is in excess: Na2SO3 + H2O + SO2 → 2NaHSO3

Describe how NaCl reacts with water

NaCl → Na+ + Cl-

Forms a neutral solution

Describe how MgCl2 reacts with water

MgCl2 + 6H2O → \[Mg(H2O)6\]2+ + 2Cl-

Forms faintly acidic solution

Describe how AlCl3 reacts with water

AlCl​3​ + 6H​2​O → \[Al(H​2​O)​6​\]​3+​ + 3Cl​-

An ​ equilibrium​ is set up with the product so H​+ ​ ions, and hence HCl, are formed:

\[Al(H​2​O)​6​\]​3+​ ​ ⇌ ​ \[Al(H​2​O)​5​(OH)\]​2+​ + H​+

Describe how SiCl4 reacts with water

SiCl​4​ + 2H​2​O → SiO​2​ + 4HCl

Violent reaction

Produces silicon dioxide and fumes of hydrogen chloride gas

Give the equation for the reaction between PCl5 and water

PCl​5​ + H​2​O → POCl​3​ + 2HCl

How does PCl5 react with boiling water?

PCl5 + 4H2O → H3PO4 + 5HCl

Describe how the bonding in group 3 oxides and chlorides are varied across the period

* sodium and magnesium form ionic bonds with oxygen and chlorine
* Aluminium forms covalent bonds with oxygen and either covalent or ionic with chlorine
* Other period 3 elements form simple covalent molecules

Why does the bonding in group 3 oxides and chlorides vary across the period?

* The difference in electronegativities between chlorine/ oxygen and the period 3 element decreases across the period.
* There is sufficient difference in the electronegativity of chlorine or oxygen and sodium or magnesium to form ions
* After aluminium the difference in electronegativity is ​ too small​ for ions to form

How can physical properties be used to predict the type of bonding in group 3 oxides and chlorides

A high ​melting point​ means that it is a giant molecular structure. This could either be ionic or covalent

What structure do group 4 elements normally have?

Giant covalent structure