Ch 7 Chemical Periodicity (Period 3)

This set of flashcards covers the physical and chemical properties of Period 3 elements, including trends in atomic/ionic radii, melting points, conductivity, electronegativity, and their reactions with water, oxygen, and the behavior of their oxides and chlorides.

Atomic Radius (Period 3 Trend)

Decreases across period 3 from sodium to chlorine because the atomic number increases, resulting in a higher positive nuclear charge that draws electrons closer.

Ionic Radius (Positive Ions)

Across period 3, the ionic radius decreases from sodium to aluminium ($Na^+$ to $Al^{3+}$) because they share the same electron configuration but have an increasing number of protons, increasing nuclear attraction.

Ionic Radius (Negative Ions)

The radius increases from silicon to chlorine ($Si^{4-}$ to $Cl^-$) because the ions have gained electrons, resulting in more electrons than protons and a weaker nuclear attraction.

Melting Point Trend (Na to Si)

Increases from sodium to silicon; sodium, magnesium, and aluminium possess giant metallic structures with increasing metal-metal bond strength, while silicon is a macromolecule with strong covalent bonds.

Melting Point Trend (P to Ar)

Decreases from phosphorus to argon; these elements are simple covalent molecules (or monatomic argon) whose melting points depend on the strength of their Van Der Waals/intermolecular forces.

Electrical Conductivity (Metals)

Increases from sodium to aluminium because the number of delocalized electrons increases, providing more charge carriers.

Electrical Conductivity (Non-metals)

Elements from silicon to chlorine are covalent compounds with no charged particles, making them non-conductors; argon is monoatomic and unable to conduct.

Electronegativity (Period 3 Trend)

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

Sodium Reaction with Water

Reacts vigorously to form a molten ball, fizzing, and producing hydrogen gas ($H_2$) and sodium hydroxide ($NaOH$). Equation: $2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g)$.

Magnesium Reaction with Steam

Reacts vigorously with steam to produce magnesium oxide ($MgO$) and hydrogen ($H_2$). Equation: $Mg(s) + H_2O(g) \rightarrow MgO(s) + H_2(g)$.

Ionic Oxides

Oxides containing the $O^{2-}$ ion, such as $Na_2O$ and $MgO$, which are strongly basic and react with water to produce hydroxide ions.

Covalent Oxides

Oxides that do not contain ions but have a strongly positive dipole that attracts water molecules to release $H^+$ ions, making them acidic (e.g., $P_4O_{10}$, $SO_3$).

Amphoteric Oxide

A substance like aluminium oxide ($Al_2O_3$) that can behave as both an acid and a base, reacting with both to form salts.

Phosphorus (V) Oxide + Water

Reacts violently with water to form phosphoric acid ($H_3PO_4$). Equation: $P_4O_{10} + 6H_2O \rightarrow 4H_3PO_4$.

Sulphur Dioxide + Water

Reacts to form an acidic solution of sulphurous acid ($H_2SO_3$) with a pH after reaction of approximately 1.

Sulphur Trioxide + Water

Reacts violently with water to produce sulphuric acid ($H_2SO_4$). Equation: $SO_3 + H_2O \rightarrow H_2SO_4$.

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 Bisulfite

The intermediate product ($NaHSO_3$) formed when sulphur dioxide reacts with sodium hydroxide ($NaOH$).

Sodium Tetrahydroxoaluminate (III)

The colourless solution ($NaAl(OH)_4$) produced when amphoteric aluminium hydroxide ($Al(OH)_3$) reacts with sodium hydroxide ($NaOH$).

Hydrolysis (Period 3 Chlorides)

The reaction of non-metal chlorides with water; simple ionic chlorides like $NaCl$ and $MgCl_2$ dissolve, while covalent chlorides react to form acidic solutions and hydrogen chloride gas.

Aluminium Chloride ($AlCl_3$) Hydrolysis

Reacts violently with water to produce misty fumes of hydrogen chloride and a pH 3 solution. Equation: $AlCl_3 + 3H_2O \rightarrow Al(OH)_3 + 3HCl$.

Silicon Tetrachloride ($SiCl_4$) Hydrolysis

Reacts violently with water to produce silicon dioxide and fumes of hydrogen chloride, forming a pH 2 solution. Equation: $SiCl_4 + 2H_2O \rightarrow SiO_2 + 4HCl$.

Phosphorus (III) Chloride ($PCl_3$) Hydrolysis

Reacts violently with water to form phosphorous acid ($H_3PO_3$) and hydrogen chloride fumes. Equation: $PCl_3 + 3H_2O \rightarrow H_3PO_3 + 3HCl$.

Disulphur Dichloride ($S_2Cl_2$) Hydrolysis

Reacts slowly with water to produce a range of products including hydrochloric acid ($HCl$), sulphur ($S$), and hydrogen sulphide ($H_2S$).