The melting point of sodium hydroxide (NaOH), commonly known as lye or caustic soda, is approximately 318 degrees Celsius (604 degrees Fahrenheit). This high melting point is due to the strong ionic bonds between the sodium and hydroxide ions within the compound. Sodium hydroxide is an ionic compound, which means it consists of positively charged sodium ions (Na+) and negatively charged hydroxide ions (OH-). These ions are held together by electrostatic forces, which are very strong and require a significant amount of energy to overcome, resulting in a high melting point.

The melting point of sodium hydroxide is influenced by several factors. Firstly, the strength of the ionic bonds plays a crucial role. The larger the charge on the ions, the stronger the electrostatic attraction between them, and thus, the higher the melting point. In the case of sodium hydroxide, the sodium ion carries a +1 charge, and the hydroxide ion carries a -1 charge, which contributes to the strong ionic bond.

Secondly, the lattice structure of the compound also affects its melting point. Sodium hydroxide has a cubic crystal lattice structure, which is a common arrangement for ionic compounds. The arrangement of ions in this lattice is highly ordered, which requires a considerable amount of energy to disrupt and melt the compound.

Additionally, the presence of water molecules can also influence the melting point of sodium hydroxide. When sodium hydroxide is dissolved in water, it forms hydrated ions, which are surrounded by water molecules. This hydration process can lower the melting point of the compound slightly, as the water molecules disrupt the ionic lattice structure to some extent.

According to the CRC Handbook of Chemistry and Physics, the melting point of anhydrous sodium hydroxide is reported to be 318 degrees Celsius (604 degrees Fahrenheit). This value is consistent with the explanation provided above, as it reflects the strong ionic bonds and the ordered lattice structure of the compound.

In conclusion, the melting point of sodium hydroxide is approximately 318 degrees Celsius due to the strong ionic bonds and the ordered lattice structure of the compound. The presence of water molecules can slightly lower the melting point, but the primary factors contributing to the high melting point are the ionic bond strength and the lattice structure.