Chemical Periodicity (Period 3) - Foundation Chemistry

Vocabulary practice flashcards covering physical and chemical trends of Period 3 elements, including radius, melting points, conductivity, and reactions of oxides and chlorides.

Atomic Radius (Period 3 Trend)

Decreases from sodium to chlorine because the atomic number increases, giving the nucleus a higher positive charge that draws electrons closer.

Ionic Radius of Positive Ions (Na to Al)

Decreases across the period because while ions have the same electron configuration, the number of protons increases, leading to higher nuclear attraction.

Ionic Radius of Negative Ions (Si to Cl)

Increases because ions have gained electrons; the nuclear attraction is weaker relative to the increased number of electrons, so they are not pulled in as strongly.

Giant Metallic Structures

The structures of sodium, magnesium, and aluminium where melting points increase across the period as metal-metal bond strength increases due to higher ion charge and smaller atomic radius.

Silicon Structure

A macromolecule with strong covalent bonds linking all its atoms together, resulting in a very high melting point.

Van Der Waals Forces

The intermolecular forces that determine the melting and boiling points of simple covalent molecules like phosphorus, sulphur, chlorine, and argon.

Electrical Conductivity (Period 3 Trend)

Increases from sodium to aluminium due to the increasing number of delocalized electrons; silicon to argon are non-conductors as they are covalent or monoatomic.

Electronegativity (Period 3 Trend)

Increases across the period due to increasing nuclei attraction on valence electrons and a decrease in atomic size.

Magnesium reaction with Steam

A vigorous reaction expressed by the equation: $Mg (s) + 2H_2O (l) \rightarrow MgO (s) + H_2 (g)$

Reaction of Chlorine with Water

Chlorine dissolves to form chlorine water as shown: $Cl_2 (aq) + H_2O (l) \rightarrow HCIO (aq) + HCl (aq)$

Basic Oxides

Ionic oxides containing the $O^{2-}$ ion, such as $Na_2O$ and $MgO$, which react with water to produce hydroxide ions and react with acids to form salts.

Amphoteric Oxide

An oxide that reacts with both acids and bases; aluminium oxide ($Al_2O_3$) is the primary example in Period 3.

Acidic Oxides

Covalent oxides that have a strongly positive dipole on the non-oxygen atom which attracts lone pairs on water to release $H^+$ ions, such as $SO_2$, $SO_3$, and $P_4O_{10}$.

Sodium Aluminate

The product formed when aluminium oxide reacts with hot concentrated sodium hydroxide: $Al_2O_3 (s) + 2NaOH (aq) + 3H_2O (l) \rightarrow 2NaAl(OH)_4 (aq)$

Sodium Silicate

A colourless solution produced when silicon dioxide reacts with hot concentrated sodium hydroxide: $SiO_2 (s) + 2NaOH (aq) \rightarrow Na_2SiO_3 (aq) + H_2O (l)$

Sodium Tetrahydroxoaluminate (III)

The product of the reaction between the amphoteric aluminium hydroxide and sodium hydroxide: $Al(OH)_3 (aq) + NaOH (aq) \rightarrow NaAl(OH)_4 (aq)$

Hydrolysis

The term used for the reactions of Period 3 chlorides with water, which vary from simple dissolution (ionic) to violent reactions producing acidic solutions (covalent).

Reaction of Phosphorus (III) Chloride with Water

A violent reaction producing phosphorous acid and hydrogen chloride fumes: $PCl_3 + 3H_2O \rightarrow H_3PO_3 + 3HCl$

Reaction of Phosphorus (V) Chloride with Water

Reacts with cold water to produce phosphorous oxychloride and hydrogen chloride: $PCl_5 + H_2O \rightarrow POCl_3 + 2HCl$

Structure of $AlCl_3$ and $PCl_5$

Substances that change their structure from ionic when solid to covalent when in liquid or vapour form.