钠

Left metal radical - the simplified side-form of 金. The indexing radical, marking 钠 as a metallic element: sodium (Na). The whole modern periodic-table column of alkali metals sits under this radical - 锂 (lithium), 钾 (potassium), 铷 (rubidium), 铯 (caesium). Inorganic element names almost always use 钅 plus a phonetic.

Right 内 supplies the sound - nèi shifting to nà through a regular nasal vowel alternation. 内 itself shows 入 (enter) under 冂 (cover), the picture of going inside. Same phonetic feeds 纳 (receive), 衲 (patched robe), 呐 (shout). Chosen here for the nà sound that approximates Latin natrium, the source of sodium's symbol Na.