Sodium (Na)

Sodium’s ground-state configuration is \([Ne]3s^1\). The single 3s valence electron is weakly held (low ionization energy), so sodium readily forms the cation \(\mathrm{Na^+}\) by losing that electron, making it highly reactive—typical of Group 1 (alkali) metals.

Sodium reacts vigorously with water to form sodium hydroxide and hydrogen gas; the heat released can ignite the hydrogen:

\(\mathrm{2\,Na(s) + 2\,H_2O(l) \rightarrow 2\,NaOH(aq) + H_2(g)}\)

Because the reaction is exothermic and the metal is soft, small pieces may melt and skitter on the water’s surface, sometimes burning with a yellow flame.

Excited sodium atoms emit strongly near 589 nm (the sodium D-lines). In a flame test, traces of Na⁺ produce an intense yellow color, which can mask other colors unless viewed through cobalt glass or a spectroscope.

By molten-salt electrolysis in the Downs cell, typically using a NaCl–CaCl₂ mixture to lower the melting point:

\(\mathrm{Na^+ + e^- \rightarrow Na(l)}\) (at the cathode)     \(\mathrm{2\,Cl^- \rightarrow Cl_2(g) + 2\,e^-}\) (at the anode)

Calcium chloride reduces energy costs by depressing the fusion temperature.

• NaCl (table salt): electrolyte balance; food preservation; chemical feedstock.
• NaOH (caustic soda): strong base for soaps, paper, biodiesel.
• NaHCO₃ (baking soda): leavening agent, mild antacid.
• Na₂CO₃ (washing soda): glass manufacture, water softening.
• NaNO₃ / NaNO₂: fertilizers, food curing (nitrite under strict limits).

In animals, \(\mathrm{Na^+}\) is the major extracellular cation. The Na⁺/K⁺ ATPase maintains ion gradients across cell membranes, enabling nerve impulse transmission, muscle contraction, and nutrient transport.

Dietary sodium is essential but excessive intake is linked to hypertension; balanced consumption is advised.

Store under dry mineral oil or an inert atmosphere to prevent reactions with moisture/air. Use dry tools and goggles; never touch with wet hands. For fires, use Class D (dry powder) extinguishers—never water or CO₂ on burning sodium.

On exposure to air, sodium forms a mixture of oxides depending on conditions: oxide \(\mathrm{Na_2O}\), peroxide \(\mathrm{Na_2O_2}\), and in oxygen-rich environments sometimes superoxide \(\mathrm{NaO_2}\) (more common for heavier alkali metals). These basic oxides react with water to produce sodium hydroxide and \(\mathrm{H_2O_2}\) (for peroxide).

Upon heating or in the presence of acids, sodium bicarbonate releases CO₂ gas, which aerates doughs/batters:

\(\mathrm{2\,NaHCO_3(s) \xrightarrow{\Delta} Na_2CO_3(s) + CO_2(g) + H_2O(g)}\)

With an acid (e.g., cream of tartar): \(\mathrm{NaHCO_3 + H^+ \rightarrow Na^+ + CO_2 + H_2O}\).

Sodium-ion (Na-ion) batteries intercalate \(\mathrm{Na^+}\) into layered or Prussian-blue-type cathodes. They use more abundant sodium, potentially lowering cost. Compared with Li-ion, Na-ion typically offers lower energy density but better performance at low temperatures and promising grid-scale storage potential.